feat: add drag_destinations for container widgets

src/widget/flex_row/widget.rs

@@ -198,6 +198,23 @@ impl<'a, Message: 'static + Clone> Widget<Message, crate::Theme, Renderer>
                 .map(|((c, c_layout), state)| c.as_widget().a11y_nodes(c_layout, state, p)),
         )
     }
+
+    fn drag_destinations(
+        &self,
+        state: &Tree,
+        layout: Layout<'_>,
+        dnd_rectangles: &mut iced_style::core::clipboard::DndDestinationRectangles,
+    ) {
+        for ((e, layout), state) in self
+            .children
+            .iter()
+            .zip(layout.children())
+            .zip(state.children.iter())
+        {
+            e.as_widget()
+                .drag_destinations(state, layout, dnd_rectangles);
+        }
+    }
 }
 
 impl<'a, Message: 'static + Clone> From<FlexRow<'a, Message>> for Element<'a, Message> {

src/widget/grid/widget.rs

@@ -263,6 +263,23 @@ impl<'a, Message: 'static + Clone> Widget<Message, crate::Theme, Renderer> for G
                 .map(|((c, c_layout), state)| c.as_widget().a11y_nodes(c_layout, state, p)),
         )
     }
+
+    fn drag_destinations(
+        &self,
+        state: &Tree,
+        layout: Layout<'_>,
+        dnd_rectangles: &mut iced_style::core::clipboard::DndDestinationRectangles,
+    ) {
+        for ((e, layout), state) in self
+            .children
+            .iter()
+            .zip(layout.children())
+            .zip(state.children.iter())
+        {
+            e.as_widget()
+                .drag_destinations(state, layout, dnd_rectangles);
+        }
+    }
 }
 
 impl<'a, Message: 'static + Clone> From<Grid<'a, Message>> for Element<'a, Message> {

src/widget/header_bar.rs

@@ -4,7 +4,7 @@
 use crate::{ext::CollectionWidget, widget, Element};
 use apply::Apply;
 use derive_setters::Setters;
-use iced::{window, Length};
+use iced::Length;
 use iced_core::{widget::tree, Widget};
 use std::borrow::Cow;
 
@@ -232,6 +232,23 @@ impl<'a, Message: Clone + 'static> Widget<Message, crate::Theme, crate::Renderer
             .as_widget_mut()
             .overlay(child_tree, child_layout, renderer)
     }
+
+    fn drag_destinations(
+        &self,
+        state: &tree::Tree,
+        layout: iced_core::Layout<'_>,
+        dnd_rectangles: &mut iced_style::core::clipboard::DndDestinationRectangles,
+    ) {
+        if let Some((child_tree, child_layout)) =
+            state.children.iter().zip(layout.children()).next()
+        {
+            self.header_bar_inner.as_widget().drag_destinations(
+                child_tree,
+                child_layout,
+                dnd_rectangles,
+            );
+        }
+    }
 }
 
 impl<'a, Message: Clone + 'static> HeaderBar<'a, Message> {

src/widget/layer_container.rs

@@ -251,6 +251,16 @@ where
     ) -> Option<overlay::Element<'b, Message, Theme, Renderer>> {
         self.container.overlay(tree, layout, renderer)
     }
+
+    fn drag_destinations(
+        &self,
+        state: &Tree,
+        layout: Layout<'_>,
+        dnd_rectangles: &mut iced_style::core::clipboard::DndDestinationRectangles,
+    ) {
+        self.container
+            .drag_destinations(state, layout, dnd_rectangles);
+    }
 }
 
 impl<'a, Message, Theme, Renderer> From<LayerContainer<'a, Message, Theme, Renderer>>

src/widget/rectangle_tracker/mod.rs

@@ -291,6 +291,16 @@ where
     ) -> Option<overlay::Element<'b, Message, crate::Theme, Renderer>> {
         self.container.overlay(tree, layout, renderer)
     }
+
+    fn drag_destinations(
+        &self,
+        state: &Tree,
+        layout: Layout<'_>,
+        dnd_rectangles: &mut iced_style::core::clipboard::DndDestinationRectangles,
+    ) {
+        self.container
+            .drag_destinations(state, layout, dnd_rectangles);
+    }
 }
 
 impl<'a, Message, Renderer, I> From<RectangleTrackingContainer<'a, Message, Renderer, I>>