Allow the user to register the application delegate on macOS and iOS (#3758)

This allows the user to override the application delegate themselves,
which opens several doors for customization that were previously closed.

To do this, we use notifications instead of top-level application delegate
methods.

One effect of not providing an application delegate on iOS is that we no
longer act as-if the application successfully open all URLs there.

This is a breaking change, although unlikely to matter in practice, since the
return value of `application:didFinishLaunchingWithOptions:` is seldom used by
the system (and is likely the preferred behaviour anyhow).

Cargo.toml

@@ -105,12 +105,12 @@ ndk = { version = "0.9.0", default-features = false }
 
 # AppKit or UIKit
 [target.'cfg(target_vendor = "apple")'.dependencies]
+block2 = "0.5.1"
 core-foundation = "0.9.3"
 objc2 = "0.5.2"
 
 # AppKit
 [target.'cfg(target_os = "macos")'.dependencies]
-block2 = "0.5.1"
 core-graphics = "0.23.1"
 objc2-app-kit = { version = "0.2.2", features = [
     "NSAppearance",
@@ -152,6 +152,7 @@ objc2-foundation = { version = "0.2.2", features = [
     "NSKeyValueObserving",
     "NSNotification",
     "NSObjCRuntime",
+    "NSOperation",
     "NSPathUtilities",
     "NSProcessInfo",
     "NSRunLoop",
@@ -163,11 +164,13 @@ objc2-foundation = { version = "0.2.2", features = [
 # UIKit
 [target.'cfg(all(target_vendor = "apple", not(target_os = "macos")))'.dependencies]
 objc2-foundation = { version = "0.2.2", features = [
+    "block2",
     "dispatch",
     "NSArray",
     "NSEnumerator",
     "NSGeometry",
     "NSObjCRuntime",
+    "NSOperation",
     "NSString",
     "NSProcessInfo",
     "NSThread",

src/changelog/unreleased.md

@@ -94,6 +94,10 @@ changelog entry.
 - Changed how `ModifiersState` is serialized by Serde.
 - `VideoModeHandle::refresh_rate_millihertz()` and `bit_depth()` now return a `Option<NonZero*>`.
 - `MonitorHandle::position()` now returns an `Option`.
+- On iOS and macOS, remove custom application delegates. You are now allowed to override the
+  application delegate yourself.
+- On iOS, no longer act as-if the application successfully open all URLs. Override
+  `application:didFinishLaunchingWithOptions:` and provide the desired behaviour yourself.
 
 ### Removed
 

src/platform/ios.rs

@@ -3,11 +3,14 @@
 //! Winit has an OS requirement of iOS 8 or higher, and is regularly tested on
 //! iOS 9.3.
 //!
+//! ## Window initialization
+//!
 //! iOS's main `UIApplicationMain` does some init work that's required by all
 //! UI-related code (see issue [#1705]). It is best to create your windows
-//! inside `Event::Resumed`.
+//! inside [`ApplicationHandler::resumed`].
 //!
 //! [#1705]: https://github.com/rust-windowing/winit/issues/1705
+//! [`ApplicationHandler::resumed`]: crate::application::ApplicationHandler::resumed
 //!
 //! ## Building app
 //!
@@ -63,6 +66,16 @@
 //! opengl will result in segfault.
 //!
 //! Also note that app may not receive the LoopExiting event if suspended; it might be SIGKILL'ed.
+//!
+//! ## Custom `UIApplicationDelegate`
+//!
+//! Winit usually handles everything related to the lifecycle events of the application. Sometimes,
+//! though, you might want to access some of the more niche stuff that [the application
+//! delegate][app-delegate] provides. This functionality is not exposed directly in Winit, since it
+//! would increase the API surface by quite a lot. Instead, Winit guarantees that it will not
+//! register an application delegate, so you can set up a custom one in a nib file instead.
+//!
+//! [app-delegate]: https://developer.apple.com/documentation/uikit/uiapplicationdelegate?language=objc
 
 use std::os::raw::c_void;
 

src/platform/macos.rs

@@ -3,16 +3,84 @@
 //! Winit has an OS requirement of macOS 10.11 or higher (same as Rust
 //! itself), and is regularly tested on macOS 10.14.
 //!
+//! ## Window initialization
+//!
 //! A lot of functionality expects the application to be ready before you
 //! start doing anything; this includes creating windows, fetching monitors,
 //! drawing, and so on, see issues [#2238], [#2051] and [#2087].
 //!
 //! If you encounter problems, you should try doing your initialization inside
-//! `Event::Resumed`.
+//! [`ApplicationHandler::resumed`].
 //!
 //! [#2238]: https://github.com/rust-windowing/winit/issues/2238
 //! [#2051]: https://github.com/rust-windowing/winit/issues/2051
 //! [#2087]: https://github.com/rust-windowing/winit/issues/2087
+//! [`ApplicationHandler::resumed`]: crate::application::ApplicationHandler::resumed
+//!
+//! ## Custom `NSApplicationDelegate`
+//!
+//! Winit usually handles everything related to the lifecycle events of the application. Sometimes,
+//! though, you might want to do more niche stuff, such as [handle when the user re-activates the
+//! application][reopen]. Such functionality is not exposed directly in Winit, since it would
+//! increase the API surface by quite a lot.
+//!
+//! [reopen]: https://developer.apple.com/documentation/appkit/nsapplicationdelegate/1428638-applicationshouldhandlereopen?language=objc
+//!
+//! Instead, Winit guarantees that it will not register an application delegate, so the solution is
+//! to register your own application delegate, as outlined in the following example (see
+//! `objc2-app-kit` for more detailed information).
+#![cfg_attr(target_os = "macos", doc = "```")]
+#![cfg_attr(not(target_os = "macos"), doc = "```ignore")]
+//! use objc2::rc::Retained;
+//! use objc2::runtime::ProtocolObject;
+//! use objc2::{declare_class, msg_send_id, mutability, ClassType, DeclaredClass};
+//! use objc2_app_kit::{NSApplication, NSApplicationDelegate};
+//! use objc2_foundation::{NSArray, NSURL, MainThreadMarker, NSObject, NSObjectProtocol};
+//! use winit::event_loop::EventLoop;
+//!
+//! declare_class!(
+//!     struct AppDelegate;
+//!
+//!     unsafe impl ClassType for AppDelegate {
+//!         type Super = NSObject;
+//!         type Mutability = mutability::MainThreadOnly;
+//!         const NAME: &'static str = "MyAppDelegate";
+//!     }
+//!
+//!     impl DeclaredClass for AppDelegate {}
+//!
+//!     unsafe impl NSObjectProtocol for AppDelegate {}
+//!
+//!     unsafe impl NSApplicationDelegate for AppDelegate {
+//!         #[method(application:openURLs:)]
+//!         fn application_openURLs(&self, application: &NSApplication, urls: &NSArray<NSURL>) {
+//!             // Note: To specifically get `application:openURLs:` to work, you _might_
+//!             // have to bundle your application. This is not done in this example.
+//!             println!("open urls: {application:?}, {urls:?}");
+//!         }
+//!     }
+//! );
+//!
+//! impl AppDelegate {
+//!     fn new(mtm: MainThreadMarker) -> Retained<Self> {
+//!         unsafe { msg_send_id![super(mtm.alloc().set_ivars(())), init] }
+//!     }
+//! }
+//!
+//! fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     let event_loop = EventLoop::new()?;
+//!
+//!     let mtm = MainThreadMarker::new().unwrap();
+//!     let delegate = AppDelegate::new(mtm);
+//!     // Important: Call `sharedApplication` after `EventLoop::new`,
+//!     // doing it before is not yet supported.
+//!     let app = NSApplication::sharedApplication(mtm);
+//!     app.setDelegate(Some(ProtocolObject::from_ref(&*delegate)));
+//!
+//!     // event_loop.run_app(&mut my_app);
+//!     Ok(())
+//! }
+//! ```
 
 use std::os::raw::c_void;
 

src/platform_impl/apple/appkit/app.rs

@@ -1,10 +1,12 @@
 #![allow(clippy::unnecessary_cast)]
 
+use std::rc::Rc;
+
 use objc2::{declare_class, msg_send, mutability, ClassType, DeclaredClass};
 use objc2_app_kit::{NSApplication, NSEvent, NSEventModifierFlags, NSEventType, NSResponder};
 use objc2_foundation::{MainThreadMarker, NSObject};
 
-use super::app_state::ApplicationDelegate;
+use super::app_state::AppState;
 use super::DEVICE_ID;
 use crate::event::{DeviceEvent, ElementState};
 
@@ -38,15 +40,15 @@ declare_class!(
                     key_window.sendEvent(event);
                 }
             } else {
-                let delegate = ApplicationDelegate::get(MainThreadMarker::from(self));
+                let app_state = AppState::get(MainThreadMarker::from(self));
-                maybe_dispatch_device_event(&delegate, event);
+                maybe_dispatch_device_event(&app_state, event);
                 unsafe { msg_send![super(self), sendEvent: event] }
             }
         }
     }
 );
 
-fn maybe_dispatch_device_event(delegate: &ApplicationDelegate, event: &NSEvent) {
+fn maybe_dispatch_device_event(app_state: &Rc<AppState>, event: &NSEvent) {
     let event_type = unsafe { event.r#type() };
     #[allow(non_upper_case_globals)]
     match event_type {
@@ -58,7 +60,7 @@ fn maybe_dispatch_device_event(delegate: &ApplicationDelegate, event: &NSEvent)
             let delta_y = unsafe { event.deltaY() } as f64;
 
             if delta_x != 0.0 || delta_y != 0.0 {
-                delegate.maybe_queue_with_handler(move |app, event_loop| {
+                app_state.maybe_queue_with_handler(move |app, event_loop| {
                     app.device_event(event_loop, DEVICE_ID, DeviceEvent::MouseMotion {
                         delta: (delta_x, delta_y),
                     });
@@ -67,7 +69,7 @@ fn maybe_dispatch_device_event(delegate: &ApplicationDelegate, event: &NSEvent)
         },
         NSEventType::LeftMouseDown | NSEventType::RightMouseDown | NSEventType::OtherMouseDown => {
             let button = unsafe { event.buttonNumber() } as u32;
-            delegate.maybe_queue_with_handler(move |app, event_loop| {
+            app_state.maybe_queue_with_handler(move |app, event_loop| {
                 app.device_event(event_loop, DEVICE_ID, DeviceEvent::Button {
                     button,
                     state: ElementState::Pressed,
@@ -76,7 +78,7 @@ fn maybe_dispatch_device_event(delegate: &ApplicationDelegate, event: &NSEvent)
         },
         NSEventType::LeftMouseUp | NSEventType::RightMouseUp | NSEventType::OtherMouseUp => {
             let button = unsafe { event.buttonNumber() } as u32;
-            delegate.maybe_queue_with_handler(move |app, event_loop| {
+            app_state.maybe_queue_with_handler(move |app, event_loop| {
                 app.device_event(event_loop, DEVICE_ID, DeviceEvent::Button {
                     button,
                     state: ElementState::Released,

src/platform_impl/apple/appkit/app_state.rs

@@ -1,14 +1,12 @@
-use std::cell::{Cell, RefCell};
+use std::cell::{Cell, OnceCell, RefCell};
 use std::mem;
-use std::rc::Weak;
+use std::rc::{Rc, Weak};
 use std::sync::atomic::{AtomicBool, Ordering as AtomicOrdering};
 use std::sync::Arc;
 use std::time::Instant;
 
-use objc2::rc::Retained;
+use objc2_app_kit::{NSApplication, NSApplicationActivationPolicy};
-use objc2::{declare_class, msg_send_id, mutability, ClassType, DeclaredClass};
+use objc2_foundation::{MainThreadMarker, NSNotification};
-use objc2_app_kit::{NSApplication, NSApplicationActivationPolicy, NSApplicationDelegate};
-use objc2_foundation::{MainThreadMarker, NSNotification, NSObject, NSObjectProtocol};
 
 use super::event_handler::EventHandler;
 use super::event_loop::{stop_app_immediately, ActiveEventLoop, PanicInfo};
@@ -21,6 +19,7 @@ use crate::window::WindowId as RootWindowId;
 
 #[derive(Debug)]
 pub(super) struct AppState {
+    mtm: MainThreadMarker,
     activation_policy: NSApplicationActivationPolicy,
     default_menu: bool,
     activate_ignoring_other_apps: bool,
@@ -46,43 +45,32 @@ pub(super) struct AppState {
     // as such should be careful to not add fields that, in turn, strongly reference those.
 }
 
-declare_class!(
+// TODO(madsmtm): Use `MainThreadBound` once that is possible in `static`s.
-    #[derive(Debug)]
+struct StaticMainThreadBound<T>(T);
-    pub(super) struct ApplicationDelegate;
 
-    unsafe impl ClassType for ApplicationDelegate {
+impl<T> StaticMainThreadBound<T> {
-        type Super = NSObject;
+    const fn get(&self, _mtm: MainThreadMarker) -> &T {
-        type Mutability = mutability::MainThreadOnly;
+        &self.0
-        const NAME: &'static str = "WinitApplicationDelegate";
     }
+}
 
-    impl DeclaredClass for ApplicationDelegate {
+unsafe impl<T> Send for StaticMainThreadBound<T> {}
-        type Ivars = AppState;
+unsafe impl<T> Sync for StaticMainThreadBound<T> {}
-    }
 
-    unsafe impl NSObjectProtocol for ApplicationDelegate {}
+// SAFETY: Creating `StaticMainThreadBound` in a `const` context, where there is no concept of the
+// main thread.
+static GLOBAL: StaticMainThreadBound<OnceCell<Rc<AppState>>> =
+    StaticMainThreadBound(OnceCell::new());
 
-    unsafe impl NSApplicationDelegate for ApplicationDelegate {
+impl AppState {
-        #[method(applicationDidFinishLaunching:)]
+    pub(super) fn setup_global(
-        fn app_did_finish_launching(&self, notification: &NSNotification) {
-            self.did_finish_launching(notification)
-        }
-
-        #[method(applicationWillTerminate:)]
-        fn app_will_terminate(&self, notification: &NSNotification) {
-            self.will_terminate(notification)
-        }
-    }
-);
-
-impl ApplicationDelegate {
-    pub(super) fn new(
         mtm: MainThreadMarker,
         activation_policy: NSApplicationActivationPolicy,
         default_menu: bool,
         activate_ignoring_other_apps: bool,
-    ) -> Retained<Self> {
+    ) -> Rc<Self> {
-        let this = mtm.alloc().set_ivars(AppState {
+        let this = Rc::new(AppState {
+            mtm,
             activation_policy,
             proxy_wake_up: Arc::new(AtomicBool::new(false)),
             default_menu,
@@ -102,33 +90,42 @@ impl ApplicationDelegate {
             wait_timeout: Cell::new(None),
             pending_redraw: RefCell::new(vec![]),
         });
-        unsafe { msg_send_id![super(this), init] }
+
+        GLOBAL.get(mtm).set(this.clone()).expect("application state can only be set once");
+        this
     }
 
-    // NOTE: This will, globally, only be run once, no matter how many
+    pub fn get(mtm: MainThreadMarker) -> Rc<Self> {
-    // `EventLoop`s the user creates.
+        GLOBAL
-    fn did_finish_launching(&self, _notification: &NSNotification) {
+            .get(mtm)
-        trace_scope!("applicationDidFinishLaunching:");
+            .get()
-        self.ivars().is_launched.set(true);
+            .expect("tried to get application state before it was registered")
+            .clone()
+    }
 
-        let mtm = MainThreadMarker::from(self);
+    // NOTE: This notification will, globally, only be emitted once,
-        let app = NSApplication::sharedApplication(mtm);
+    // no matter how many `EventLoop`s the user creates.
+    pub fn did_finish_launching(self: &Rc<Self>, _notification: &NSNotification) {
+        trace_scope!("NSApplicationDidFinishLaunchingNotification");
+        self.is_launched.set(true);
+
+        let app = NSApplication::sharedApplication(self.mtm);
         // We need to delay setting the activation policy and activating the app
         // until `applicationDidFinishLaunching` has been called. Otherwise the
         // menu bar is initially unresponsive on macOS 10.15.
-        app.setActivationPolicy(self.ivars().activation_policy);
+        app.setActivationPolicy(self.activation_policy);
 
         window_activation_hack(&app);
         #[allow(deprecated)]
-        app.activateIgnoringOtherApps(self.ivars().activate_ignoring_other_apps);
+        app.activateIgnoringOtherApps(self.activate_ignoring_other_apps);
 
-        if self.ivars().default_menu {
+        if self.default_menu {
             // The menubar initialization should be before the `NewEvents` event, to allow
             // overriding of the default menu even if it's created
             menu::initialize(&app);
         }
 
-        self.ivars().waker.borrow_mut().start();
+        self.waker.borrow_mut().start();
 
         self.set_is_running(true);
         self.dispatch_init_events();
@@ -138,77 +135,65 @@ impl ApplicationDelegate {
         //
         // In this case we still want to consider Winit's `EventLoop` to be "running",
         // so we call `start_running()` above.
-        if self.ivars().stop_on_launch.get() {
+        if self.stop_on_launch.get() {
             // NOTE: the original idea had been to only stop the underlying `RunLoop`
             // for the app but that didn't work as expected (`-[NSApplication run]`
             // effectively ignored the attempt to stop the RunLoop and re-started it).
             //
             // So we return from `pump_events` by stopping the application.
-            let app = NSApplication::sharedApplication(mtm);
+            let app = NSApplication::sharedApplication(self.mtm);
             stop_app_immediately(&app);
         }
     }
 
-    fn will_terminate(&self, _notification: &NSNotification) {
+    pub fn will_terminate(self: &Rc<Self>, _notification: &NSNotification) {
-        trace_scope!("applicationWillTerminate:");
+        trace_scope!("NSApplicationWillTerminateNotification");
         // TODO: Notify every window that it will be destroyed, like done in iOS?
         self.internal_exit();
     }
 
-    pub fn get(mtm: MainThreadMarker) -> Retained<Self> {
+    /// Place the event handler in the application state for the duration
-        let app = NSApplication::sharedApplication(mtm);
-        let delegate =
-            unsafe { app.delegate() }.expect("a delegate was not configured on the application");
-        if delegate.is_kind_of::<Self>() {
-            // SAFETY: Just checked that the delegate is an instance of `ApplicationDelegate`
-            unsafe { Retained::cast(delegate) }
-        } else {
-            panic!("tried to get a delegate that was not the one Winit has registered")
-        }
-    }
-
-    /// Place the event handler in the application delegate for the duration
     /// of the given closure.
     pub fn set_event_handler<R>(
         &self,
         handler: &mut dyn ApplicationHandler,
         closure: impl FnOnce() -> R,
     ) -> R {
-        self.ivars().event_handler.set(handler, closure)
+        self.event_handler.set(handler, closure)
     }
 
     pub fn proxy_wake_up(&self) -> Arc<AtomicBool> {
-        self.ivars().proxy_wake_up.clone()
+        self.proxy_wake_up.clone()
     }
 
     /// If `pump_events` is called to progress the event loop then we
     /// bootstrap the event loop via `-[NSApplication run]` but will use
     /// `CFRunLoopRunInMode` for subsequent calls to `pump_events`.
     pub fn set_stop_on_launch(&self) {
-        self.ivars().stop_on_launch.set(true);
+        self.stop_on_launch.set(true);
     }
 
     pub fn set_stop_before_wait(&self, value: bool) {
-        self.ivars().stop_before_wait.set(value)
+        self.stop_before_wait.set(value)
     }
 
     pub fn set_stop_after_wait(&self, value: bool) {
-        self.ivars().stop_after_wait.set(value)
+        self.stop_after_wait.set(value)
     }
 
     pub fn set_stop_on_redraw(&self, value: bool) {
-        self.ivars().stop_on_redraw.set(value)
+        self.stop_on_redraw.set(value)
     }
 
     pub fn set_wait_timeout(&self, value: Option<Instant>) {
-        self.ivars().wait_timeout.set(value)
+        self.wait_timeout.set(value)
     }
 
     /// Clears the `running` state and resets the `control_flow` state when an `EventLoop` exits.
     ///
     /// NOTE: that if the `NSApplication` has been launched then that state is preserved,
     /// and we won't need to re-launch the app if subsequent EventLoops are run.
-    pub fn internal_exit(&self) {
+    pub fn internal_exit(self: &Rc<Self>) {
         self.with_handler(|app, event_loop| {
             app.exiting(event_loop);
         });
@@ -221,42 +206,41 @@ impl ApplicationDelegate {
     }
 
     pub fn is_launched(&self) -> bool {
-        self.ivars().is_launched.get()
+        self.is_launched.get()
     }
 
     pub fn set_is_running(&self, value: bool) {
-        self.ivars().is_running.set(value)
+        self.is_running.set(value)
     }
 
     pub fn is_running(&self) -> bool {
-        self.ivars().is_running.get()
+        self.is_running.get()
     }
 
     pub fn exit(&self) {
-        self.ivars().exit.set(true)
+        self.exit.set(true)
     }
 
     pub fn clear_exit(&self) {
-        self.ivars().exit.set(false)
+        self.exit.set(false)
     }
 
     pub fn exiting(&self) -> bool {
-        self.ivars().exit.get()
+        self.exit.get()
     }
 
     pub fn set_control_flow(&self, value: ControlFlow) {
-        self.ivars().control_flow.set(value)
+        self.control_flow.set(value)
     }
 
     pub fn control_flow(&self) -> ControlFlow {
-        self.ivars().control_flow.get()
+        self.control_flow.get()
     }
 
-    pub fn handle_redraw(&self, window_id: WindowId) {
+    pub fn handle_redraw(self: &Rc<Self>, window_id: WindowId) {
-        let mtm = MainThreadMarker::from(self);
         // Redraw request might come out of order from the OS.
         // -> Don't go back into the event handler when our callstack originates from there
-        if !self.ivars().event_handler.in_use() {
+        if !self.event_handler.in_use() {
             self.with_handler(|app, event_loop| {
                 app.window_event(event_loop, RootWindowId(window_id), WindowEvent::RedrawRequested);
             });
@@ -264,24 +248,24 @@ impl ApplicationDelegate {
             // `pump_events` will request to stop immediately _after_ dispatching RedrawRequested
             // events as a way to ensure that `pump_events` can't block an external loop
             // indefinitely
-            if self.ivars().stop_on_redraw.get() {
+            if self.stop_on_redraw.get() {
-                let app = NSApplication::sharedApplication(mtm);
+                let app = NSApplication::sharedApplication(self.mtm);
                 stop_app_immediately(&app);
             }
         }
     }
 
     pub fn queue_redraw(&self, window_id: WindowId) {
-        let mut pending_redraw = self.ivars().pending_redraw.borrow_mut();
+        let mut pending_redraw = self.pending_redraw.borrow_mut();
         if !pending_redraw.contains(&window_id) {
             pending_redraw.push(window_id);
         }
-        self.ivars().run_loop.wakeup();
+        self.run_loop.wakeup();
     }
 
     #[track_caller]
     pub fn maybe_queue_with_handler(
-        &self,
+        self: &Rc<Self>,
         callback: impl FnOnce(&mut dyn ApplicationHandler, &ActiveEventLoop) + 'static,
     ) {
         // Most programmer actions in AppKit (e.g. change window fullscreen, set focused, etc.)
@@ -290,26 +274,28 @@ impl ApplicationDelegate {
         // However, it is not documented which actions do this, and which ones are done immediately,
         // so to make sure that we don't encounter re-entrancy issues, we first check if we're
         // currently handling another event, and if we are, we queue the event instead.
-        if !self.ivars().event_handler.in_use() {
+        if !self.event_handler.in_use() {
             self.with_handler(callback);
         } else {
             tracing::debug!("had to queue event since another is currently being handled");
-            let this = self.retain();
+            let this = Rc::clone(self);
-            self.ivars().run_loop.queue_closure(move || {
+            self.run_loop.queue_closure(move || {
                 this.with_handler(callback);
             });
         }
     }
 
     #[track_caller]
-    fn with_handler(&self, callback: impl FnOnce(&mut dyn ApplicationHandler, &ActiveEventLoop)) {
+    fn with_handler(
-        let event_loop =
+        self: &Rc<Self>,
-            ActiveEventLoop { delegate: self.retain(), mtm: MainThreadMarker::from(self) };
+        callback: impl FnOnce(&mut dyn ApplicationHandler, &ActiveEventLoop),
-        self.ivars().event_handler.handle(callback, &event_loop);
+    ) {
+        let event_loop = ActiveEventLoop { app_state: Rc::clone(self), mtm: self.mtm };
+        self.event_handler.handle(callback, &event_loop);
     }
 
     /// dispatch `NewEvents(Init)` + `Resumed`
-    pub fn dispatch_init_events(&self) {
+    pub fn dispatch_init_events(self: &Rc<Self>) {
         self.with_handler(|app, event_loop| app.new_events(event_loop, StartCause::Init));
         // NB: For consistency all platforms must call `can_create_surfaces` even though macOS
         // applications don't themselves have a formal surface destroy/create lifecycle.
@@ -317,23 +303,22 @@ impl ApplicationDelegate {
     }
 
     // Called by RunLoopObserver after finishing waiting for new events
-    pub fn wakeup(&self, panic_info: Weak<PanicInfo>) {
+    pub fn wakeup(self: &Rc<Self>, panic_info: Weak<PanicInfo>) {
-        let mtm = MainThreadMarker::from(self);
         let panic_info = panic_info
             .upgrade()
             .expect("The panic info must exist here. This failure indicates a developer error.");
 
         // Return when in event handler due to https://github.com/rust-windowing/winit/issues/1779
-        if panic_info.is_panicking() || !self.ivars().event_handler.ready() || !self.is_running() {
+        if panic_info.is_panicking() || !self.event_handler.ready() || !self.is_running() {
             return;
         }
 
-        if self.ivars().stop_after_wait.get() {
+        if self.stop_after_wait.get() {
-            let app = NSApplication::sharedApplication(mtm);
+            let app = NSApplication::sharedApplication(self.mtm);
             stop_app_immediately(&app);
         }
 
-        let start = self.ivars().start_time.get().unwrap();
+        let start = self.start_time.get().unwrap();
         let cause = match self.control_flow() {
             ControlFlow::Poll => StartCause::Poll,
             ControlFlow::Wait => StartCause::WaitCancelled { start, requested_resume: None },
@@ -350,8 +335,7 @@ impl ApplicationDelegate {
     }
 
     // Called by RunLoopObserver before waiting for new events
-    pub fn cleared(&self, panic_info: Weak<PanicInfo>) {
+    pub fn cleared(self: &Rc<Self>, panic_info: Weak<PanicInfo>) {
-        let mtm = MainThreadMarker::from(self);
         let panic_info = panic_info
             .upgrade()
             .expect("The panic info must exist here. This failure indicates a developer error.");
@@ -359,15 +343,15 @@ impl ApplicationDelegate {
         // Return when in event handler due to https://github.com/rust-windowing/winit/issues/1779
         // XXX: how does it make sense that `event_handler.ready()` can ever return `false` here if
         // we're about to return to the `CFRunLoop` to poll for new events?
-        if panic_info.is_panicking() || !self.ivars().event_handler.ready() || !self.is_running() {
+        if panic_info.is_panicking() || !self.event_handler.ready() || !self.is_running() {
             return;
         }
 
-        if self.ivars().proxy_wake_up.swap(false, AtomicOrdering::Relaxed) {
+        if self.proxy_wake_up.swap(false, AtomicOrdering::Relaxed) {
             self.with_handler(|app, event_loop| app.proxy_wake_up(event_loop));
         }
 
-        let redraw = mem::take(&mut *self.ivars().pending_redraw.borrow_mut());
+        let redraw = mem::take(&mut *self.pending_redraw.borrow_mut());
         for window_id in redraw {
             self.with_handler(|app, event_loop| {
                 app.window_event(event_loop, RootWindowId(window_id), WindowEvent::RedrawRequested);
@@ -378,22 +362,22 @@ impl ApplicationDelegate {
         });
 
         if self.exiting() {
-            let app = NSApplication::sharedApplication(mtm);
+            let app = NSApplication::sharedApplication(self.mtm);
             stop_app_immediately(&app);
         }
 
-        if self.ivars().stop_before_wait.get() {
+        if self.stop_before_wait.get() {
-            let app = NSApplication::sharedApplication(mtm);
+            let app = NSApplication::sharedApplication(self.mtm);
             stop_app_immediately(&app);
         }
-        self.ivars().start_time.set(Some(Instant::now()));
+        self.start_time.set(Some(Instant::now()));
-        let wait_timeout = self.ivars().wait_timeout.get(); // configured by pump_events
+        let wait_timeout = self.wait_timeout.get(); // configured by pump_events
         let app_timeout = match self.control_flow() {
             ControlFlow::Wait => None,
             ControlFlow::Poll => Some(Instant::now()),
             ControlFlow::WaitUntil(instant) => Some(instant),
         };
-        self.ivars().waker.borrow_mut().start_at(min_timeout(wait_timeout, app_timeout));
+        self.waker.borrow_mut().start_at(min_timeout(wait_timeout, app_timeout));
     }
 }
 

src/platform_impl/apple/appkit/event_handler.rs

@@ -124,7 +124,7 @@ impl EventHandler {
                 callback(*user_app, event_loop);
             },
             Ok(None) => {
-                // `NSApplication`, our app delegate and this handler are all
+                // `NSApplication`, our app state and this handler are all
                 // global state and so it's not impossible that we could get
                 // an event after the application has exited the `EventLoop`.
                 tracing::error!("tried to run event handler, but no handler was set");

src/platform_impl/apple/appkit/event_loop.rs

@@ -14,13 +14,16 @@ use core_foundation::runloop::{
     CFRunLoopSourceCreate, CFRunLoopSourceRef, CFRunLoopSourceSignal, CFRunLoopWakeUp,
 };
 use objc2::rc::{autoreleasepool, Retained};
-use objc2::runtime::ProtocolObject;
 use objc2::{msg_send_id, sel, ClassType};
-use objc2_app_kit::{NSApplication, NSApplicationActivationPolicy, NSWindow};
+use objc2_app_kit::{
-use objc2_foundation::{MainThreadMarker, NSObjectProtocol};
+    NSApplication, NSApplicationActivationPolicy, NSApplicationDidFinishLaunchingNotification,
+    NSApplicationWillTerminateNotification, NSWindow,
+};
+use objc2_foundation::{MainThreadMarker, NSNotificationCenter, NSObject, NSObjectProtocol};
 
+use super::super::notification_center::create_observer;
 use super::app::WinitApplication;
-use super::app_state::ApplicationDelegate;
+use super::app_state::AppState;
 use super::cursor::CustomCursor;
 use super::event::dummy_event;
 use super::monitor;
@@ -71,15 +74,11 @@ impl PanicInfo {
 
 #[derive(Debug)]
 pub struct ActiveEventLoop {
-    pub(super) delegate: Retained<ApplicationDelegate>,
+    pub(super) app_state: Rc<AppState>,
     pub(super) mtm: MainThreadMarker,
 }
 
 impl ActiveEventLoop {
-    pub(super) fn app_delegate(&self) -> &ApplicationDelegate {
-        &self.delegate
-    }
-
     pub(crate) fn hide_application(&self) {
         NSApplication::sharedApplication(self.mtm).hide(None)
     }
@@ -99,7 +98,7 @@ impl ActiveEventLoop {
 
 impl RootActiveEventLoop for ActiveEventLoop {
     fn create_proxy(&self) -> RootEventLoopProxy {
-        let event_loop_proxy = EventLoopProxy::new(self.delegate.proxy_wake_up());
+        let event_loop_proxy = EventLoopProxy::new(self.app_state.proxy_wake_up());
         RootEventLoopProxy { event_loop_proxy }
     }
 
@@ -140,19 +139,19 @@ impl RootActiveEventLoop for ActiveEventLoop {
     }
 
     fn set_control_flow(&self, control_flow: ControlFlow) {
-        self.delegate.set_control_flow(control_flow)
+        self.app_state.set_control_flow(control_flow)
     }
 
     fn control_flow(&self) -> ControlFlow {
-        self.delegate.control_flow()
+        self.app_state.control_flow()
     }
 
     fn exit(&self) {
-        self.delegate.exit()
+        self.app_state.exit()
     }
 
     fn exiting(&self) -> bool {
-        self.delegate.exiting()
+        self.app_state.exiting()
     }
 
     fn owned_display_handle(&self) -> RootOwnedDisplayHandle {
@@ -179,14 +178,17 @@ pub struct EventLoop {
     /// We intentionally don't store `WinitApplication` since we want to have
     /// the possibility of swapping that out at some point.
     app: Retained<NSApplication>,
-    /// The application delegate that we've registered.
+    app_state: Rc<AppState>,
-    ///
-    /// The delegate is only weakly referenced by NSApplication, so we must
-    /// keep it around here as well.
-    delegate: Retained<ApplicationDelegate>,
 
     window_target: ActiveEventLoop,
     panic_info: Rc<PanicInfo>,
+
+    // Since macOS 10.11, we no longer need to remove the observers before they are deallocated;
+    // the system instead cleans it up next time it would have posted a notification to it.
+    //
+    // Though we do still need to keep the observers around to prevent them from being deallocated.
+    _did_finish_launching_observer: Retained<NSObject>,
+    _will_terminate_observer: Retained<NSObject>,
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -229,25 +231,49 @@ impl EventLoop {
             ActivationPolicy::Prohibited => NSApplicationActivationPolicy::Prohibited,
         };
 
-        let delegate = ApplicationDelegate::new(
+        let app_state = AppState::setup_global(
             mtm,
             activation_policy,
             attributes.default_menu,
             attributes.activate_ignoring_other_apps,
         );
 
-        autoreleasepool(|_| {
+        let center = unsafe { NSNotificationCenter::defaultCenter() };
-            app.setDelegate(Some(ProtocolObject::from_ref(&*delegate)));
+
-        });
+        let weak_app_state = Rc::downgrade(&app_state);
+        let _did_finish_launching_observer = create_observer(
+            &center,
+            // `applicationDidFinishLaunching:`
+            unsafe { NSApplicationDidFinishLaunchingNotification },
+            move |notification| {
+                if let Some(app_state) = weak_app_state.upgrade() {
+                    app_state.did_finish_launching(notification);
+                }
+            },
+        );
+
+        let weak_app_state = Rc::downgrade(&app_state);
+        let _will_terminate_observer = create_observer(
+            &center,
+            // `applicationWillTerminate:`
+            unsafe { NSApplicationWillTerminateNotification },
+            move |notification| {
+                if let Some(app_state) = weak_app_state.upgrade() {
+                    app_state.will_terminate(notification);
+                }
+            },
+        );
 
         let panic_info: Rc<PanicInfo> = Default::default();
         setup_control_flow_observers(mtm, Rc::downgrade(&panic_info));
 
         Ok(EventLoop {
             app,
-            delegate: delegate.clone(),
+            app_state: app_state.clone(),
-            window_target: ActiveEventLoop { delegate, mtm },
+            window_target: ActiveEventLoop { app_state, mtm },
             panic_info,
+            _did_finish_launching_observer,
+            _will_terminate_observer,
         })
     }
 
@@ -267,19 +293,19 @@ impl EventLoop {
         &mut self,
         mut app: A,
     ) -> Result<(), EventLoopError> {
-        self.delegate.clear_exit();
+        self.app_state.clear_exit();
-        self.delegate.set_event_handler(&mut app, || {
+        self.app_state.set_event_handler(&mut app, || {
             autoreleasepool(|_| {
                 // clear / normalize pump_events state
-                self.delegate.set_wait_timeout(None);
+                self.app_state.set_wait_timeout(None);
-                self.delegate.set_stop_before_wait(false);
+                self.app_state.set_stop_before_wait(false);
-                self.delegate.set_stop_after_wait(false);
+                self.app_state.set_stop_after_wait(false);
-                self.delegate.set_stop_on_redraw(false);
+                self.app_state.set_stop_on_redraw(false);
 
-                if self.delegate.is_launched() {
+                if self.app_state.is_launched() {
-                    debug_assert!(!self.delegate.is_running());
+                    debug_assert!(!self.app_state.is_running());
-                    self.delegate.set_is_running(true);
+                    self.app_state.set_is_running(true);
-                    self.delegate.dispatch_init_events();
+                    self.app_state.dispatch_init_events();
                 }
 
                 // SAFETY: We do not run the application re-entrantly
@@ -294,7 +320,7 @@ impl EventLoop {
                     resume_unwind(panic);
                 }
 
-                self.delegate.internal_exit()
+                self.app_state.internal_exit()
             })
         });
 
@@ -306,47 +332,47 @@ impl EventLoop {
         timeout: Option<Duration>,
         mut app: A,
     ) -> PumpStatus {
-        self.delegate.set_event_handler(&mut app, || {
+        self.app_state.set_event_handler(&mut app, || {
             autoreleasepool(|_| {
                 // As a special case, if the application hasn't been launched yet then we at least
                 // run the loop until it has fully launched.
-                if !self.delegate.is_launched() {
+                if !self.app_state.is_launched() {
-                    debug_assert!(!self.delegate.is_running());
+                    debug_assert!(!self.app_state.is_running());
 
-                    self.delegate.set_stop_on_launch();
+                    self.app_state.set_stop_on_launch();
                     // SAFETY: We do not run the application re-entrantly
                     unsafe { self.app.run() };
 
                     // Note: we dispatch `NewEvents(Init)` + `Resumed` events after the application
                     // has launched
-                } else if !self.delegate.is_running() {
+                } else if !self.app_state.is_running() {
                     // Even though the application may have been launched, it's possible we aren't
                     // running if the `EventLoop` was run before and has since
                     // exited. This indicates that we just starting to re-run
                     // the same `EventLoop` again.
-                    self.delegate.set_is_running(true);
+                    self.app_state.set_is_running(true);
-                    self.delegate.dispatch_init_events();
+                    self.app_state.dispatch_init_events();
                 } else {
                     // Only run for as long as the given `Duration` allows so we don't block the
                     // external loop.
                     match timeout {
                         Some(Duration::ZERO) => {
-                            self.delegate.set_wait_timeout(None);
+                            self.app_state.set_wait_timeout(None);
-                            self.delegate.set_stop_before_wait(true);
+                            self.app_state.set_stop_before_wait(true);
                         },
                         Some(duration) => {
-                            self.delegate.set_stop_before_wait(false);
+                            self.app_state.set_stop_before_wait(false);
                             let timeout = Instant::now() + duration;
-                            self.delegate.set_wait_timeout(Some(timeout));
+                            self.app_state.set_wait_timeout(Some(timeout));
-                            self.delegate.set_stop_after_wait(true);
+                            self.app_state.set_stop_after_wait(true);
                         },
                         None => {
-                            self.delegate.set_wait_timeout(None);
+                            self.app_state.set_wait_timeout(None);
-                            self.delegate.set_stop_before_wait(false);
+                            self.app_state.set_stop_before_wait(false);
-                            self.delegate.set_stop_after_wait(true);
+                            self.app_state.set_stop_after_wait(true);
                         },
                     }
-                    self.delegate.set_stop_on_redraw(true);
+                    self.app_state.set_stop_on_redraw(true);
                     // SAFETY: We do not run the application re-entrantly
                     unsafe { self.app.run() };
                 }
@@ -360,8 +386,8 @@ impl EventLoop {
                     resume_unwind(panic);
                 }
 
-                if self.delegate.exiting() {
+                if self.app_state.exiting() {
-                    self.delegate.internal_exit();
+                    self.app_state.internal_exit();
                     PumpStatus::Exit(0)
                 } else {
                     PumpStatus::Continue

src/platform_impl/apple/appkit/observer.rs

@@ -22,7 +22,7 @@ use core_foundation::runloop::{
 use objc2_foundation::MainThreadMarker;
 use tracing::error;
 
-use super::app_state::ApplicationDelegate;
+use super::app_state::AppState;
 use super::event_loop::{stop_app_on_panic, PanicInfo};
 use super::ffi;
 
@@ -59,7 +59,7 @@ extern "C" fn control_flow_begin_handler(
             match activity {
                 kCFRunLoopAfterWaiting => {
                     // trace!("Triggered `CFRunLoopAfterWaiting`");
-                    ApplicationDelegate::get(MainThreadMarker::new().unwrap()).wakeup(panic_info);
+                    AppState::get(MainThreadMarker::new().unwrap()).wakeup(panic_info);
                     // trace!("Completed `CFRunLoopAfterWaiting`");
                 },
                 _ => unreachable!(),
@@ -81,7 +81,7 @@ extern "C" fn control_flow_end_handler(
             match activity {
                 kCFRunLoopBeforeWaiting => {
                     // trace!("Triggered `CFRunLoopBeforeWaiting`");
-                    ApplicationDelegate::get(MainThreadMarker::new().unwrap()).cleared(panic_info);
+                    AppState::get(MainThreadMarker::new().unwrap()).cleared(panic_info);
                     // trace!("Completed `CFRunLoopBeforeWaiting`");
                 },
                 kCFRunLoopExit => (), // unimplemented!(), // not expected to ever happen

src/platform_impl/apple/appkit/view.rs

@@ -2,6 +2,7 @@
 use std::cell::{Cell, RefCell};
 use std::collections::{HashMap, VecDeque};
 use std::ptr;
+use std::rc::Rc;
 
 use objc2::rc::{Retained, WeakId};
 use objc2::runtime::{AnyObject, Sel};
@@ -16,7 +17,7 @@ use objc2_foundation::{
     NSPoint, NSRange, NSRect, NSSize, NSString, NSUInteger,
 };
 
-use super::app_state::ApplicationDelegate;
+use super::app_state::AppState;
 use super::cursor::{default_cursor, invisible_cursor};
 use super::event::{
     code_to_key, code_to_location, create_key_event, event_mods, lalt_pressed, ralt_pressed,
@@ -112,7 +113,7 @@ fn get_left_modifier_code(key: &Key) -> KeyCode {
 #[derive(Debug)]
 pub struct ViewState {
     /// Strong reference to the global application state.
-    app_delegate: Retained<ApplicationDelegate>,
+    app_state: Rc<AppState>,
 
     cursor_state: RefCell<CursorState>,
     ime_position: Cell<NSPoint>,
@@ -206,7 +207,7 @@ declare_class!(
 
             // It's a workaround for https://github.com/rust-windowing/winit/issues/2640, don't replace with `self.window_id()`.
             if let Some(window) = self.ivars()._ns_window.load() {
-                self.ivars().app_delegate.handle_redraw(window.id());
+                self.ivars().app_state.handle_redraw(window.id());
             }
 
             // This is a direct subclass of NSView, no need to call superclass' drawRect:
@@ -687,7 +688,7 @@ declare_class!(
 
             self.update_modifiers(event, false);
 
-            self.ivars().app_delegate.maybe_queue_with_handler(move |app, event_loop|
+            self.ivars().app_state.maybe_queue_with_handler(move |app, event_loop|
                 app.device_event(event_loop, DEVICE_ID, DeviceEvent::MouseWheel { delta })
             );
             self.queue_event(WindowEvent::MouseWheel {
@@ -782,14 +783,14 @@ declare_class!(
 
 impl WinitView {
     pub(super) fn new(
-        app_delegate: &ApplicationDelegate,
+        app_state: &Rc<AppState>,
         window: &WinitWindow,
         accepts_first_mouse: bool,
         option_as_alt: OptionAsAlt,
     ) -> Retained<Self> {
         let mtm = MainThreadMarker::from(window);
         let this = mtm.alloc().set_ivars(ViewState {
-            app_delegate: app_delegate.retain(),
+            app_state: Rc::clone(app_state),
             cursor_state: Default::default(),
             ime_position: Default::default(),
             ime_size: Default::default(),
@@ -834,7 +835,7 @@ impl WinitView {
 
     fn queue_event(&self, event: WindowEvent) {
         let window_id = RootWindowId(self.window().id());
-        self.ivars().app_delegate.maybe_queue_with_handler(move |app, event_loop| {
+        self.ivars().app_state.maybe_queue_with_handler(move |app, event_loop| {
             app.window_event(event_loop, window_id, event);
         });
     }

src/platform_impl/apple/appkit/window.rs

@@ -28,9 +28,8 @@ impl Window {
         attributes: WindowAttributes,
     ) -> Result<Self, RootOsError> {
         let mtm = window_target.mtm;
-        let delegate = autoreleasepool(|_| {
+        let delegate =
-            WindowDelegate::new(window_target.app_delegate(), attributes, mtm)
+            autoreleasepool(|_| WindowDelegate::new(&window_target.app_state, attributes, mtm))?;
-        })?;
         Ok(Window {
             window: MainThreadBound::new(delegate.window().retain(), mtm),
             delegate: MainThreadBound::new(delegate, mtm),

src/platform_impl/apple/appkit/window_delegate.rs

@@ -3,6 +3,7 @@ use std::cell::{Cell, RefCell};
 use std::collections::VecDeque;
 use std::ffi::c_void;
 use std::ptr;
+use std::rc::Rc;
 use std::sync::{Arc, Mutex};
 
 use core_graphics::display::{CGDisplay, CGPoint};
@@ -26,7 +27,7 @@ use objc2_foundation::{
 };
 use tracing::{trace, warn};
 
-use super::app_state::ApplicationDelegate;
+use super::app_state::AppState;
 use super::cursor::cursor_from_icon;
 use super::monitor::{self, flip_window_screen_coordinates, get_display_id};
 use super::observer::RunLoop;
@@ -79,7 +80,7 @@ impl Default for PlatformSpecificWindowAttributes {
 #[derive(Debug)]
 pub(crate) struct State {
     /// Strong reference to the global application state.
-    app_delegate: Retained<ApplicationDelegate>,
+    app_state: Rc<AppState>,
 
     window: Retained<WinitWindow>,
 
@@ -482,7 +483,7 @@ impl Drop for WindowDelegate {
 }
 
 fn new_window(
-    app_delegate: &ApplicationDelegate,
+    app_state: &Rc<AppState>,
     attrs: &WindowAttributes,
     mtm: MainThreadMarker,
 ) -> Option<Retained<WinitWindow>> {
@@ -622,7 +623,7 @@ fn new_window(
         }
 
         let view = WinitView::new(
-            app_delegate,
+            app_state,
             &window,
             attrs.platform_specific.accepts_first_mouse,
             attrs.platform_specific.option_as_alt,
@@ -665,11 +666,11 @@ fn new_window(
 
 impl WindowDelegate {
     pub(super) fn new(
-        app_delegate: &ApplicationDelegate,
+        app_state: &Rc<AppState>,
         attrs: WindowAttributes,
         mtm: MainThreadMarker,
     ) -> Result<Retained<Self>, RootOsError> {
-        let window = new_window(app_delegate, &attrs, mtm)
+        let window = new_window(app_state, &attrs, mtm)
             .ok_or_else(|| os_error!(OsError::CreationError("couldn't create `NSWindow`")))?;
 
         #[cfg(feature = "rwh_06")]
@@ -709,7 +710,7 @@ impl WindowDelegate {
         }
 
         let delegate = mtm.alloc().set_ivars(State {
-            app_delegate: app_delegate.retain(),
+            app_state: Rc::clone(app_state),
             window: window.retain(),
             previous_position: Cell::new(None),
             previous_scale_factor: Cell::new(scale_factor),
@@ -808,7 +809,7 @@ impl WindowDelegate {
 
     pub(crate) fn queue_event(&self, event: WindowEvent) {
         let window_id = RootWindowId(self.window().id());
-        self.ivars().app_delegate.maybe_queue_with_handler(move |app, event_loop| {
+        self.ivars().app_state.maybe_queue_with_handler(move |app, event_loop| {
             app.window_event(event_loop, window_id, event);
         });
     }
@@ -907,7 +908,7 @@ impl WindowDelegate {
     }
 
     pub fn request_redraw(&self) {
-        self.ivars().app_delegate.queue_redraw(self.window().id());
+        self.ivars().app_state.queue_redraw(self.window().id());
     }
 
     #[inline]

src/platform_impl/apple/mod.rs

@@ -2,6 +2,7 @@
 
 #[cfg(target_os = "macos")]
 mod appkit;
+mod notification_center;
 #[cfg(not(target_os = "macos"))]
 mod uikit;
 

src/platform_impl/apple/notification_center.rs

@@ -0,0 +1,27 @@
+use std::ptr::NonNull;
+
+use block2::RcBlock;
+use objc2::rc::Retained;
+use objc2_foundation::{NSNotification, NSNotificationCenter, NSNotificationName, NSObject};
+
+/// Observe the given notification.
+///
+/// This is used in Winit as an alternative to declaring an application delegate, as we want to
+/// give the user full control over those.
+pub fn create_observer(
+    center: &NSNotificationCenter,
+    name: &NSNotificationName,
+    handler: impl Fn(&NSNotification) + 'static,
+) -> Retained<NSObject> {
+    let block = RcBlock::new(move |notification: NonNull<NSNotification>| {
+        handler(unsafe { notification.as_ref() });
+    });
+    unsafe {
+        center.addObserverForName_object_queue_usingBlock(
+            Some(name),
+            None, // No sender filter
+            None, // No queue, run on posting thread (i.e. main thread)
+            &block,
+        )
+    }
+}

src/platform_impl/apple/uikit/app_delegate.rs

@@ -1,60 +0,0 @@
-use objc2::{declare_class, mutability, ClassType, DeclaredClass};
-use objc2_foundation::{MainThreadMarker, NSObject};
-use objc2_ui_kit::UIApplication;
-
-use super::app_state::{self, send_occluded_event_for_all_windows, EventWrapper};
-use crate::event::Event;
-
-declare_class!(
-    pub struct AppDelegate;
-
-    unsafe impl ClassType for AppDelegate {
-        type Super = NSObject;
-        type Mutability = mutability::InteriorMutable;
-        const NAME: &'static str = "WinitApplicationDelegate";
-    }
-
-    impl DeclaredClass for AppDelegate {}
-
-    // UIApplicationDelegate protocol
-    unsafe impl AppDelegate {
-        #[method(application:didFinishLaunchingWithOptions:)]
-        fn did_finish_launching(&self, _application: &UIApplication, _: *mut NSObject) -> bool {
-            app_state::did_finish_launching(MainThreadMarker::new().unwrap());
-            true
-        }
-
-        #[method(applicationDidBecomeActive:)]
-        fn did_become_active(&self, _application: &UIApplication) {
-            let mtm = MainThreadMarker::new().unwrap();
-            app_state::handle_nonuser_event(mtm, EventWrapper::StaticEvent(Event::Resumed))
-        }
-
-        #[method(applicationWillResignActive:)]
-        fn will_resign_active(&self, _application: &UIApplication) {
-            let mtm = MainThreadMarker::new().unwrap();
-            app_state::handle_nonuser_event(mtm, EventWrapper::StaticEvent(Event::Suspended))
-        }
-
-        #[method(applicationWillEnterForeground:)]
-        fn will_enter_foreground(&self, application: &UIApplication) {
-            send_occluded_event_for_all_windows(application, false);
-        }
-
-        #[method(applicationDidEnterBackground:)]
-        fn did_enter_background(&self, application: &UIApplication) {
-            send_occluded_event_for_all_windows(application, true);
-        }
-
-        #[method(applicationWillTerminate:)]
-        fn will_terminate(&self, application: &UIApplication) {
-            app_state::terminated(application);
-        }
-
-        #[method(applicationDidReceiveMemoryWarning:)]
-        fn did_receive_memory_warning(&self, _application: &UIApplication) {
-            let mtm = MainThreadMarker::new().unwrap();
-            app_state::handle_nonuser_event(mtm, EventWrapper::StaticEvent(Event::MemoryWarning))
-        }
-    }
-);

src/platform_impl/apple/uikit/event_loop.rs

@@ -12,11 +12,19 @@ use core_foundation::runloop::{
 };
 use objc2::rc::Retained;
 use objc2::{msg_send_id, ClassType};
-use objc2_foundation::{MainThreadMarker, NSString};
+use objc2_foundation::{MainThreadMarker, NSNotificationCenter, NSObject};
-use objc2_ui_kit::{UIApplication, UIApplicationMain, UIScreen};
+use objc2_ui_kit::{
+    UIApplication, UIApplicationDidBecomeActiveNotification,
+    UIApplicationDidEnterBackgroundNotification, UIApplicationDidFinishLaunchingNotification,
+    UIApplicationDidReceiveMemoryWarningNotification, UIApplicationMain,
+    UIApplicationWillEnterForegroundNotification, UIApplicationWillResignActiveNotification,
+    UIApplicationWillTerminateNotification, UIScreen,
+};
 
-use super::app_delegate::AppDelegate;
+use super::super::notification_center::create_observer;
-use super::app_state::{AppState, EventLoopHandler};
+use super::app_state::{
+    send_occluded_event_for_all_windows, AppState, EventLoopHandler, EventWrapper,
+};
 use super::{app_state, monitor, MonitorHandle};
 use crate::application::ApplicationHandler;
 use crate::error::{EventLoopError, ExternalError, NotSupportedError, OsError};
@@ -149,6 +157,18 @@ fn map_user_event<'a, A: ApplicationHandler + 'a>(
 pub struct EventLoop {
     mtm: MainThreadMarker,
     window_target: ActiveEventLoop,
+
+    // Since iOS 9.0, we no longer need to remove the observers before they are deallocated; the
+    // system instead cleans it up next time it would have posted a notification to it.
+    //
+    // Though we do still need to keep the observers around to prevent them from being deallocated.
+    _did_finish_launching_observer: Retained<NSObject>,
+    _did_become_active_observer: Retained<NSObject>,
+    _will_resign_active_observer: Retained<NSObject>,
+    _will_enter_foreground_observer: Retained<NSObject>,
+    _did_enter_background_observer: Retained<NSObject>,
+    _will_terminate_observer: Retained<NSObject>,
+    _did_receive_memory_warning_observer: Retained<NSObject>,
 }
 
 #[derive(Default, Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -173,7 +193,96 @@ impl EventLoop {
         // this line sets up the main run loop before `UIApplicationMain`
         setup_control_flow_observers();
 
-        Ok(EventLoop { mtm, window_target: ActiveEventLoop { mtm } })
+        let center = unsafe { NSNotificationCenter::defaultCenter() };
+
+        let _did_finish_launching_observer = create_observer(
+            &center,
+            // `application:didFinishLaunchingWithOptions:`
+            unsafe { UIApplicationDidFinishLaunchingNotification },
+            move |_| {
+                app_state::did_finish_launching(mtm);
+            },
+        );
+        let _did_become_active_observer = create_observer(
+            &center,
+            // `applicationDidBecomeActive:`
+            unsafe { UIApplicationDidBecomeActiveNotification },
+            move |_| {
+                app_state::handle_nonuser_event(mtm, EventWrapper::StaticEvent(Event::Resumed));
+            },
+        );
+        let _will_resign_active_observer = create_observer(
+            &center,
+            // `applicationWillResignActive:`
+            unsafe { UIApplicationWillResignActiveNotification },
+            move |_| {
+                app_state::handle_nonuser_event(mtm, EventWrapper::StaticEvent(Event::Suspended));
+            },
+        );
+        let _will_enter_foreground_observer = create_observer(
+            &center,
+            // `applicationWillEnterForeground:`
+            unsafe { UIApplicationWillEnterForegroundNotification },
+            move |notification| {
+                let app = unsafe { notification.object() }.expect(
+                    "UIApplicationWillEnterForegroundNotification to have application object",
+                );
+                // SAFETY: The `object` in `UIApplicationWillEnterForegroundNotification` is
+                // documented to be `UIApplication`.
+                let app: Retained<UIApplication> = unsafe { Retained::cast(app) };
+                send_occluded_event_for_all_windows(&app, false);
+            },
+        );
+        let _did_enter_background_observer = create_observer(
+            &center,
+            // `applicationDidEnterBackground:`
+            unsafe { UIApplicationDidEnterBackgroundNotification },
+            move |notification| {
+                let app = unsafe { notification.object() }.expect(
+                    "UIApplicationDidEnterBackgroundNotification to have application object",
+                );
+                // SAFETY: The `object` in `UIApplicationDidEnterBackgroundNotification` is
+                // documented to be `UIApplication`.
+                let app: Retained<UIApplication> = unsafe { Retained::cast(app) };
+                send_occluded_event_for_all_windows(&app, true);
+            },
+        );
+        let _will_terminate_observer = create_observer(
+            &center,
+            // `applicationWillTerminate:`
+            unsafe { UIApplicationWillTerminateNotification },
+            move |notification| {
+                let app = unsafe { notification.object() }
+                    .expect("UIApplicationWillTerminateNotification to have application object");
+                // SAFETY: The `object` in `UIApplicationWillTerminateNotification` is
+                // (somewhat) documented to be `UIApplication`.
+                let app: Retained<UIApplication> = unsafe { Retained::cast(app) };
+                app_state::terminated(&app);
+            },
+        );
+        let _did_receive_memory_warning_observer = create_observer(
+            &center,
+            // `applicationDidReceiveMemoryWarning:`
+            unsafe { UIApplicationDidReceiveMemoryWarningNotification },
+            move |_| {
+                app_state::handle_nonuser_event(
+                    mtm,
+                    EventWrapper::StaticEvent(Event::MemoryWarning),
+                );
+            },
+        );
+
+        Ok(EventLoop {
+            mtm,
+            window_target: ActiveEventLoop { mtm },
+            _did_finish_launching_observer,
+            _did_become_active_observer,
+            _will_resign_active_observer,
+            _will_enter_foreground_observer,
+            _did_enter_background_observer,
+            _will_terminate_observer,
+            _did_receive_memory_warning_observer,
+        })
     }
 
     pub fn run_app<A: ApplicationHandler>(self, app: A) -> ! {
@@ -199,9 +308,6 @@ impl EventLoop {
 
         app_state::will_launch(self.mtm, handler);
 
-        // Ensure application delegate is initialized
-        let _ = AppDelegate::class();
-
         extern "C" {
             // These functions are in crt_externs.h.
             fn _NSGetArgc() -> *mut c_int;
@@ -212,8 +318,10 @@ impl EventLoop {
             UIApplicationMain(
                 *_NSGetArgc(),
                 NonNull::new(*_NSGetArgv()).unwrap(),
+                // We intentionally override neither the application nor the delegate, to allow the
+                // user to do so themselves!
+                None,
                 None,
-                Some(&NSString::from_str(AppDelegate::NAME)),
             )
         };
         unreachable!()

src/platform_impl/apple/uikit/mod.rs

@@ -1,6 +1,5 @@
 #![allow(clippy::let_unit_value)]
 
-mod app_delegate;
 mod app_state;
 mod event_loop;
 mod monitor;