Introduce `Shell` type in `iced_native`

Widgets now can invalidate the current layout of the application on demand.

24 files changed, 203 insertions, 117 deletions

diff --git a/native/src/element.rs b/native/src/element.rs
index ee404a1c..7e806b08 100644
--- a/native/src/element.rs
+++ b/native/src/element.rs
@@ -4,7 +4,7 @@ use crate::mouse;
 use crate::overlay;
 use crate::renderer;
 use crate::{
-    Clipboard, Color, Hasher, Layout, Length, Point, Rectangle, Widget,
+    Clipboard, Color, Hasher, Layout, Length, Point, Rectangle, Shell, Widget,
 };
 
 /// A generic [`Widget`].
@@ -228,7 +228,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         self.widget.on_event(
             event,
@@ -236,7 +236,7 @@ where
             cursor_position,
             renderer,
             clipboard,
-            messages,
+            shell,
         )
     }
 
@@ -327,9 +327,10 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<B>,
+        shell: &mut Shell<'_, B>,
     ) -> event::Status {
-        let mut original_messages = Vec::new();
+        let mut local_messages = Vec::new();
+        let mut local_shell = Shell::new(&mut local_messages);
 
         let status = self.widget.on_event(
             event,
@@ -337,12 +338,10 @@ where
             cursor_position,
             renderer,
             clipboard,
-            &mut original_messages,
+            &mut local_shell,
         );
 
-        original_messages
-            .drain(..)
-            .for_each(|message| messages.push((self.mapper)(message)));
+        shell.merge(local_shell, &self.mapper);
 
         status
     }
@@ -427,7 +426,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         self.element.widget.on_event(
             event,
@@ -435,7 +434,7 @@ where
             cursor_position,
             renderer,
             clipboard,
-            messages,
+            shell,
         )
     }
 
diff --git a/native/src/lib.rs b/native/src/lib.rs
index 51b232e9..f340ec14 100644
--- a/native/src/lib.rs
+++ b/native/src/lib.rs
@@ -53,6 +53,7 @@ pub mod window;
 mod element;
 mod hasher;
 mod runtime;
+mod shell;
 mod user_interface;
 
 // We disable debug capabilities on release builds unless the `debug` feature
@@ -85,6 +86,7 @@ pub use overlay::Overlay;
 pub use program::Program;
 pub use renderer::Renderer;
 pub use runtime::Runtime;
+pub use shell::Shell;
 pub use subscription::Subscription;
 pub use user_interface::{Cache, UserInterface};
 pub use widget::Widget;
diff --git a/native/src/overlay.rs b/native/src/overlay.rs
index 1ac3cea5..e66d421a 100644
--- a/native/src/overlay.rs
+++ b/native/src/overlay.rs
@@ -10,7 +10,7 @@ use crate::event::{self, Event};
 use crate::layout;
 use crate::mouse;
 use crate::renderer;
-use crate::{Clipboard, Hasher, Layout, Point, Rectangle, Size};
+use crate::{Clipboard, Hasher, Layout, Point, Rectangle, Shell, Size};
 
 /// An interactive component that can be displayed on top of other widgets.
 pub trait Overlay<Message, Renderer>
@@ -71,7 +71,7 @@ where
         _cursor_position: Point,
         _renderer: &Renderer,
         _clipboard: &mut dyn Clipboard,
-        _messages: &mut Vec<Message>,
+        _shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         event::Status::Ignored
     }
diff --git a/native/src/overlay/element.rs b/native/src/overlay/element.rs
index 24b39ced..70cb417e 100644
--- a/native/src/overlay/element.rs
+++ b/native/src/overlay/element.rs
@@ -4,7 +4,7 @@ use crate::event::{self, Event};
 use crate::layout;
 use crate::mouse;
 use crate::renderer;
-use crate::{Clipboard, Hasher, Layout, Point, Rectangle, Size, Vector};
+use crate::{Clipboard, Hasher, Layout, Point, Rectangle, Shell, Size, Vector};
 
 /// A generic [`Overlay`].
 #[allow(missing_debug_implementations)]
@@ -62,7 +62,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         self.overlay.on_event(
             event,
@@ -70,7 +70,7 @@ where
             cursor_position,
             renderer,
             clipboard,
-            messages,
+            shell,
         )
     }
 
@@ -136,9 +136,10 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<B>,
+        shell: &mut Shell<'_, B>,
     ) -> event::Status {
-        let mut original_messages = Vec::new();
+        let mut local_messages = Vec::new();
+        let mut local_shell = Shell::new(&mut local_messages);
 
         let event_status = self.content.on_event(
             event,
@@ -146,12 +147,10 @@ where
             cursor_position,
             renderer,
             clipboard,
-            &mut original_messages,
+            &mut local_shell,
         );
 
-        original_messages
-            .drain(..)
-            .for_each(|message| messages.push((self.mapper)(message)));
+        shell.merge(local_shell, self.mapper);
 
         event_status
     }
diff --git a/native/src/overlay/menu.rs b/native/src/overlay/menu.rs
index ee3bee6e..6776a3ee 100644
--- a/native/src/overlay/menu.rs
+++ b/native/src/overlay/menu.rs
@@ -11,7 +11,7 @@ use crate::widget::scrollable::{self, Scrollable};
 use crate::widget::Container;
 use crate::{
     Clipboard, Color, Element, Hasher, Layout, Length, Padding, Point,
-    Rectangle, Size, Vector, Widget,
+    Rectangle, Shell, Size, Vector, Widget,
 };
 
 pub use iced_style::menu::Style;
@@ -222,7 +222,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         self.container.on_event(
             event.clone(),
@@ -230,7 +230,7 @@ where
             cursor_position,
             renderer,
             clipboard,
-            messages,
+            shell,
         )
     }
 
@@ -333,7 +333,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         _clipboard: &mut dyn Clipboard,
-        _messages: &mut Vec<Message>,
+        _shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         match event {
             Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left)) => {
diff --git a/native/src/shell.rs b/native/src/shell.rs
new file mode 100644
index 00000000..e916f52d
--- /dev/null
+++ b/native/src/shell.rs
@@ -0,0 +1,54 @@
+/// A connection to the state of a shell.
+///
+/// A [`Widget`] can leverage a [`Shell`] to trigger changes in an application,
+/// like publishing messages or invalidating the current layout.
+///
+/// [`Widget`]: crate::Widget
+#[derive(Debug)]
+pub struct Shell<'a, Message> {
+    messages: &'a mut Vec<Message>,
+    is_layout_invalid: bool,
+}
+
+impl<'a, Message> Shell<'a, Message> {
+    /// Creates a new [`Shell`] with the provided buffer of messages.
+    pub fn new(messages: &'a mut Vec<Message>) -> Self {
+        Self {
+            messages,
+            is_layout_invalid: false,
+        }
+    }
+
+    /// Triggers the given function if the layout is invalid, cleaning it in the
+    /// process.
+    pub fn with_invalid_layout(&mut self, f: impl FnOnce()) {
+        if self.is_layout_invalid {
+            self.is_layout_invalid = false;
+
+            f()
+        }
+    }
+
+    /// Publish the given `Message` for an application to process it.
+    pub fn publish(&mut self, message: Message) {
+        self.messages.push(message);
+    }
+
+    /// Invalidates the current application layout.
+    ///
+    /// The shell will relayout the application widgets.
+    pub fn invalidate_layout(&mut self) {
+        self.is_layout_invalid = true;
+    }
+
+    /// Merges the current [`Shell`] with another one by applying the given
+    /// function to the messages of the latter.
+    ///
+    /// This method is useful for composition.
+    pub fn merge<B>(&mut self, other: Shell<'_, B>, f: impl Fn(B) -> Message) {
+        self.messages.extend(other.messages.drain(..).map(f));
+
+        self.is_layout_invalid =
+            self.is_layout_invalid || other.is_layout_invalid;
+    }
+}
diff --git a/native/src/user_interface.rs b/native/src/user_interface.rs
index f44ed1fb..5d24bf4f 100644
--- a/native/src/user_interface.rs
+++ b/native/src/user_interface.rs
@@ -3,7 +3,7 @@ use crate::layout;
 use crate::mouse;
 use crate::overlay;
 use crate::renderer;
-use crate::{Clipboard, Element, Layout, Point, Rectangle, Size};
+use crate::{Clipboard, Element, Layout, Point, Rectangle, Shell, Size};
 
 use std::hash::Hasher;
 
@@ -179,7 +179,7 @@ where
     ///     let event_statuses = user_interface.update(
     ///         &events,
     ///         cursor_position,
-    ///         &renderer,
+    ///         &mut renderer,
     ///         &mut clipboard,
     ///         &mut messages
     ///     );
@@ -196,16 +196,18 @@ where
         &mut self,
         events: &[Event],
         cursor_position: Point,
-        renderer: &Renderer,
+        renderer: &mut Renderer,
         clipboard: &mut dyn Clipboard,
         messages: &mut Vec<Message>,
     ) -> Vec<event::Status> {
         let (base_cursor, overlay_statuses) = if let Some(mut overlay) =
             self.root.overlay(Layout::new(&self.base.layout))
         {
-            let layer = Self::overlay_layer(
+            let bounds = self.bounds;
+
+            let mut layer = Self::overlay_layer(
                 self.overlay.take(),
-                self.bounds,
+                bounds,
                 &mut overlay,
                 renderer,
             );
@@ -214,14 +216,27 @@ where
                 .iter()
                 .cloned()
                 .map(|event| {
-                    overlay.on_event(
+                    let mut shell = Shell::new(messages);
+
+                    let event_status = overlay.on_event(
                         event,
                         Layout::new(&layer.layout),
                         cursor_position,
                         renderer,
                         clipboard,
-                        messages,
-                    )
+                        &mut shell,
+                    );
+
+                    shell.with_invalid_layout(|| {
+                        layer = Self::overlay_layer(
+                            None,
+                            bounds,
+                            &mut overlay,
+                            renderer,
+                        );
+                    });
+
+                    event_status
                 })
                 .collect();
 
@@ -245,15 +260,34 @@ where
             .cloned()
             .zip(overlay_statuses.into_iter())
             .map(|(event, overlay_status)| {
+                let mut shell = Shell::new(messages);
+
                 let event_status = self.root.widget.on_event(
                     event,
                     Layout::new(&self.base.layout),
                     base_cursor,
                     renderer,
                     clipboard,
-                    messages,
+                    &mut shell,
                 );
 
+                shell.with_invalid_layout(|| {
+                    let hash = {
+                        let hasher = &mut crate::Hasher::default();
+                        self.root.hash_layout(hasher);
+
+                        hasher.finish()
+                    };
+
+                    let layout = renderer.layout(
+                        &self.root,
+                        &layout::Limits::new(Size::ZERO, self.bounds),
+                    );
+
+                    self.base = Layer { layout, hash };
+                    self.overlay = None;
+                });
+
                 event_status.merge(overlay_status)
             })
             .collect()
@@ -313,7 +347,7 @@ where
     ///     let event_statuses = user_interface.update(
     ///         &events,
     ///         cursor_position,
-    ///         &renderer,
+    ///         &mut renderer,
     ///         &mut clipboard,
     ///         &mut messages
     ///     );
diff --git a/native/src/widget.rs b/native/src/widget.rs
index 07214b16..e2613e67 100644
--- a/native/src/widget.rs
+++ b/native/src/widget.rs
@@ -75,7 +75,7 @@ use crate::layout;
 use crate::mouse;
 use crate::overlay;
 use crate::renderer;
-use crate::{Clipboard, Hasher, Layout, Length, Point, Rectangle};
+use crate::{Clipboard, Hasher, Layout, Length, Point, Rectangle, Shell};
 
 /// A component that displays information and allows interaction.
 ///
@@ -163,7 +163,7 @@ where
         _cursor_position: Point,
         _renderer: &Renderer,
         _clipboard: &mut dyn Clipboard,
-        _messages: &mut Vec<Message>,
+        _shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         event::Status::Ignored
     }
diff --git a/native/src/widget/button.rs b/native/src/widget/button.rs
index 1d785f35..686289e4 100644
--- a/native/src/widget/button.rs
+++ b/native/src/widget/button.rs
@@ -9,7 +9,7 @@ use crate::renderer;
 use crate::touch;
 use crate::{
     Background, Clipboard, Color, Element, Hasher, Layout, Length, Padding,
-    Point, Rectangle, Vector, Widget,
+    Point, Rectangle, Shell, Vector, Widget,
 };
 
 use std::hash::Hash;
@@ -197,7 +197,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         if let event::Status::Captured = self.content.on_event(
             event.clone(),
@@ -205,7 +205,7 @@ where
             cursor_position,
             renderer,
             clipboard,
-            messages,
+            shell,
         ) {
             return event::Status::Captured;
         }
@@ -232,7 +232,7 @@ where
                         self.state.is_pressed = false;
 
                         if bounds.contains(cursor_position) {
-                            messages.push(on_press);
+                            shell.publish(on_press);
                         }
 
                         return event::Status::Captured;
diff --git a/native/src/widget/checkbox.rs b/native/src/widget/checkbox.rs
index 81611426..2af2d60c 100644
--- a/native/src/widget/checkbox.rs
+++ b/native/src/widget/checkbox.rs
@@ -11,7 +11,7 @@ use crate::touch;
 use crate::widget::{self, Row, Text};
 use crate::{
     Alignment, Clipboard, Color, Element, Hasher, Layout, Length, Point,
-    Rectangle, Widget,
+    Rectangle, Shell, Widget,
 };
 
 pub use iced_style::checkbox::{Style, StyleSheet};
@@ -171,7 +171,7 @@ where
         cursor_position: Point,
         _renderer: &Renderer,
         _clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         match event {
             Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
@@ -179,7 +179,7 @@ where
                 let mouse_over = layout.bounds().contains(cursor_position);
 
                 if mouse_over {
-                    messages.push((self.on_toggle)(!self.is_checked));
+                    shell.publish((self.on_toggle)(!self.is_checked));
 
                     return event::Status::Captured;
                 }
diff --git a/native/src/widget/column.rs b/native/src/widget/column.rs
index 0d4d6fa7..4c43c8c8 100644
--- a/native/src/widget/column.rs
+++ b/native/src/widget/column.rs
@@ -8,7 +8,7 @@ use crate::overlay;
 use crate::renderer;
 use crate::{
     Alignment, Clipboard, Element, Hasher, Layout, Length, Padding, Point,
-    Rectangle, Widget,
+    Rectangle, Shell, Widget,
 };
 
 use std::u32;
@@ -146,7 +146,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         self.children
             .iter_mut()
@@ -158,7 +158,7 @@ where
                     cursor_position,
                     renderer,
                     clipboard,
-                    messages,
+                    shell,
                 )
             })
             .fold(event::Status::Ignored, event::Status::merge)
diff --git a/native/src/widget/container.rs b/native/src/widget/container.rs
index 596af7fd..756d9d1b 100644
--- a/native/src/widget/container.rs
+++ b/native/src/widget/container.rs
@@ -9,7 +9,7 @@ use crate::overlay;
 use crate::renderer;
 use crate::{
     Background, Clipboard, Color, Element, Hasher, Layout, Length, Padding,
-    Point, Rectangle, Widget,
+    Point, Rectangle, Shell, Widget,
 };
 
 use std::u32;
@@ -167,7 +167,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         self.content.widget.on_event(
             event,
@@ -175,7 +175,7 @@ where
             cursor_position,
             renderer,
             clipboard,
-            messages,
+            shell,
         )
     }
 
diff --git a/native/src/widget/image/viewer.rs b/native/src/widget/image/viewer.rs
index 95e5c6e4..0fc766c3 100644
--- a/native/src/widget/image/viewer.rs
+++ b/native/src/widget/image/viewer.rs
@@ -5,8 +5,8 @@ use crate::layout;
 use crate::mouse;
 use crate::renderer;
 use crate::{
-    Clipboard, Element, Hasher, Layout, Length, Point, Rectangle, Size, Vector,
-    Widget,
+    Clipboard, Element, Hasher, Layout, Length, Point, Rectangle, Shell, Size,
+    Vector, Widget,
 };
 
 use std::hash::Hash;
@@ -169,7 +169,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         _clipboard: &mut dyn Clipboard,
-        _messages: &mut Vec<Message>,
+        _shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         let bounds = layout.bounds();
         let is_mouse_over = bounds.contains(cursor_position);
diff --git a/native/src/widget/pane_grid.rs b/native/src/widget/pane_grid.rs
index 3637822b..24b87eed 100644
--- a/native/src/widget/pane_grid.rs
+++ b/native/src/widget/pane_grid.rs
@@ -34,8 +34,8 @@ use crate::overlay;
 use crate::renderer;
 use crate::touch;
 use crate::{
-    Clipboard, Color, Element, Hasher, Layout, Length, Point, Rectangle, Size,
-    Vector, Widget,
+    Clipboard, Color, Element, Hasher, Layout, Length, Point, Rectangle, Shell,
+    Size, Vector, Widget,
 };
 
 pub use iced_style::pane_grid::{Line, StyleSheet};
@@ -205,7 +205,7 @@ where
         &mut self,
         layout: Layout<'_>,
         cursor_position: Point,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) {
         let mut clicked_region =
             self.elements.iter().zip(layout.children()).filter(
@@ -214,7 +214,7 @@ where
 
         if let Some(((pane, content), layout)) = clicked_region.next() {
             if let Some(on_click) = &self.on_click {
-                messages.push(on_click(*pane));
+                shell.publish(on_click(*pane));
             }
 
             if let Some(on_drag) = &self.on_drag {
@@ -226,7 +226,7 @@ where
 
                     self.state.pick_pane(pane, origin);
 
-                    messages.push(on_drag(DragEvent::Picked { pane: *pane }));
+                    shell.publish(on_drag(DragEvent::Picked { pane: *pane }));
                 }
             }
         }
@@ -236,7 +236,7 @@ where
         &mut self,
         layout: Layout<'_>,
         cursor_position: Point,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         if let Some((_, on_resize)) = &self.on_resize {
             if let Some((split, _)) = self.state.picked_split() {
@@ -263,7 +263,7 @@ where
                         }
                     };
 
-                    messages.push(on_resize(ResizeEvent { split, ratio }));
+                    shell.publish(on_resize(ResizeEvent { split, ratio }));
 
                     return event::Status::Captured;
                 }
@@ -362,7 +362,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         let mut event_status = event::Status::Ignored;
 
@@ -395,15 +395,11 @@ where
                             if let Some((split, axis, _)) = clicked_split {
                                 self.state.pick_split(&split, axis);
                             } else {
-                                self.click_pane(
-                                    layout,
-                                    cursor_position,
-                                    messages,
-                                );
+                                self.click_pane(layout, cursor_position, shell);
                             }
                         }
                         None => {
-                            self.click_pane(layout, cursor_position, messages);
+                            self.click_pane(layout, cursor_position, shell);
                         }
                     }
                 }
@@ -430,7 +426,7 @@ where
                             _ => DragEvent::Canceled { pane },
                         };
 
-                        messages.push(on_drag(event));
+                        shell.publish(on_drag(event));
                     }
 
                     self.state.idle();
@@ -445,7 +441,7 @@ where
             Event::Mouse(mouse::Event::CursorMoved { .. })
             | Event::Touch(touch::Event::FingerMoved { .. }) => {
                 event_status =
-                    self.trigger_resize(layout, cursor_position, messages);
+                    self.trigger_resize(layout, cursor_position, shell);
             }
             _ => {}
         }
@@ -464,7 +460,7 @@ where
                     cursor_position,
                     renderer,
                     clipboard,
-                    messages,
+                    shell,
                     is_picked,
                 )
             })
diff --git a/native/src/widget/pane_grid/content.rs b/native/src/widget/pane_grid/content.rs
index c44506dd..533827b7 100644
--- a/native/src/widget/pane_grid/content.rs
+++ b/native/src/widget/pane_grid/content.rs
@@ -5,7 +5,9 @@ use crate::overlay;
 use crate::renderer;
 use crate::widget::container;
 use crate::widget::pane_grid::TitleBar;
-use crate::{Clipboard, Element, Hasher, Layout, Point, Rectangle, Size};
+use crate::{
+    Clipboard, Element, Hasher, Layout, Point, Rectangle, Shell, Size,
+};
 
 /// The content of a [`Pane`].
 ///
@@ -160,7 +162,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
         is_picked: bool,
     ) -> event::Status {
         let mut event_status = event::Status::Ignored;
@@ -174,7 +176,7 @@ where
                 cursor_position,
                 renderer,
                 clipboard,
-                messages,
+                shell,
             );
 
             children.next().unwrap()
@@ -191,7 +193,7 @@ where
                 cursor_position,
                 renderer,
                 clipboard,
-                messages,
+                shell,
             )
         };
 
diff --git a/native/src/widget/pane_grid/title_bar.rs b/native/src/widget/pane_grid/title_bar.rs
index 070cf404..353e1ce9 100644
--- a/native/src/widget/pane_grid/title_bar.rs
+++ b/native/src/widget/pane_grid/title_bar.rs
@@ -5,7 +5,7 @@ use crate::overlay;
 use crate::renderer;
 use crate::widget::container;
 use crate::{
-    Clipboard, Element, Hasher, Layout, Padding, Point, Rectangle, Size,
+    Clipboard, Element, Hasher, Layout, Padding, Point, Rectangle, Shell, Size,
 };
 
 /// The title bar of a [`Pane`].
@@ -218,7 +218,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         let mut children = layout.children();
         let padded = children.next().unwrap();
@@ -235,7 +235,7 @@ where
                 cursor_position,
                 renderer,
                 clipboard,
-                messages,
+                shell,
             )
         } else {
             event::Status::Ignored
@@ -247,7 +247,7 @@ where
             cursor_position,
             renderer,
             clipboard,
-            messages,
+            shell,
         );
 
         control_status.merge(title_status)
diff --git a/native/src/widget/pick_list.rs b/native/src/widget/pick_list.rs
index 9d1a86ec..cb781a89 100644
--- a/native/src/widget/pick_list.rs
+++ b/native/src/widget/pick_list.rs
@@ -11,7 +11,7 @@ use crate::text::{self, Text};
 use crate::touch;
 use crate::{
     Clipboard, Element, Hasher, Layout, Length, Padding, Point, Rectangle,
-    Size, Widget,
+    Shell, Size, Widget,
 };
 use std::borrow::Cow;
 
@@ -245,7 +245,7 @@ where
         cursor_position: Point,
         _renderer: &Renderer,
         _clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         match event {
             Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
@@ -271,7 +271,7 @@ where
                 };
 
                 if let Some(last_selection) = self.last_selection.take() {
-                    messages.push((self.on_selected)(last_selection));
+                    shell.publish((self.on_selected)(last_selection));
 
                     *self.is_open = false;
 
@@ -312,7 +312,7 @@ where
                 };
 
                 if let Some(next_option) = next_option {
-                    messages.push((self.on_selected)(next_option.clone()));
+                    shell.publish((self.on_selected)(next_option.clone()));
                 }
 
                 event::Status::Captured
diff --git a/native/src/widget/radio.rs b/native/src/widget/radio.rs
index 86ad4c4e..523773bd 100644
--- a/native/src/widget/radio.rs
+++ b/native/src/widget/radio.rs
@@ -11,7 +11,7 @@ use crate::touch;
 use crate::widget::{self, Row, Text};
 use crate::{
     Alignment, Clipboard, Color, Element, Hasher, Layout, Length, Point,
-    Rectangle, Widget,
+    Rectangle, Shell, Widget,
 };
 
 pub use iced_style::radio::{Style, StyleSheet};
@@ -187,13 +187,13 @@ where
         cursor_position: Point,
         _renderer: &Renderer,
         _clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         match event {
             Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
             | Event::Touch(touch::Event::FingerPressed { .. }) => {
                 if layout.bounds().contains(cursor_position) {
-                    messages.push(self.on_click.clone());
+                    shell.publish(self.on_click.clone());
 
                     return event::Status::Captured;
                 }
diff --git a/native/src/widget/row.rs b/native/src/widget/row.rs
index 6fe3284b..a0174f79 100644
--- a/native/src/widget/row.rs
+++ b/native/src/widget/row.rs
@@ -6,7 +6,7 @@ use crate::overlay;
 use crate::renderer;
 use crate::{
     Alignment, Clipboard, Element, Hasher, Layout, Length, Padding, Point,
-    Rectangle, Widget,
+    Rectangle, Shell, Widget,
 };
 
 use std::hash::Hash;
@@ -145,7 +145,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         self.children
             .iter_mut()
@@ -157,7 +157,7 @@ where
                     cursor_position,
                     renderer,
                     clipboard,
-                    messages,
+                    shell,
                 )
             })
             .fold(event::Status::Ignored, event::Status::merge)
diff --git a/native/src/widget/scrollable.rs b/native/src/widget/scrollable.rs
index 2bf2ea5e..fac8af9e 100644
--- a/native/src/widget/scrollable.rs
+++ b/native/src/widget/scrollable.rs
@@ -8,7 +8,7 @@ use crate::touch;
 use crate::widget::Column;
 use crate::{
     Alignment, Background, Clipboard, Color, Element, Hasher, Layout, Length,
-    Padding, Point, Rectangle, Size, Vector, Widget,
+    Padding, Point, Rectangle, Shell, Size, Vector, Widget,
 };
 
 use std::{f32, hash::Hash, u32};
@@ -144,14 +144,14 @@ impl<'a, Message, Renderer: crate::Renderer> Scrollable<'a, Message, Renderer> {
         &self,
         bounds: Rectangle,
         content_bounds: Rectangle,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) {
         if content_bounds.height <= bounds.height {
             return;
         }
 
         if let Some(on_scroll) = &self.on_scroll {
-            messages.push(on_scroll(
+            shell.publish(on_scroll(
                 self.state.offset.absolute(bounds, content_bounds)
                     / (content_bounds.height - bounds.height),
             ));
@@ -251,7 +251,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         let bounds = layout.bounds();
         let is_mouse_over = bounds.contains(cursor_position);
@@ -286,7 +286,7 @@ where
                 cursor_position,
                 renderer,
                 clipboard,
-                messages,
+                shell,
             )
         };
 
@@ -307,7 +307,7 @@ where
                         }
                     }
 
-                    self.notify_on_scroll(bounds, content_bounds, messages);
+                    self.notify_on_scroll(bounds, content_bounds, shell);
 
                     return event::Status::Captured;
                 }
@@ -336,7 +336,7 @@ where
                                 self.notify_on_scroll(
                                     bounds,
                                     content_bounds,
-                                    messages,
+                                    shell,
                                 );
                             }
                         }
@@ -377,7 +377,7 @@ where
                             content_bounds,
                         );
 
-                        self.notify_on_scroll(bounds, content_bounds, messages);
+                        self.notify_on_scroll(bounds, content_bounds, shell);
 
                         return event::Status::Captured;
                     }
@@ -409,7 +409,7 @@ where
                             self.notify_on_scroll(
                                 bounds,
                                 content_bounds,
-                                messages,
+                                shell,
                             );
 
                             return event::Status::Captured;
diff --git a/native/src/widget/slider.rs b/native/src/widget/slider.rs
index 3ce53f6c..65632a5c 100644
--- a/native/src/widget/slider.rs
+++ b/native/src/widget/slider.rs
@@ -8,7 +8,7 @@ use crate::renderer;
 use crate::touch;
 use crate::{
     Background, Clipboard, Color, Element, Hasher, Layout, Length, Point,
-    Rectangle, Size, Widget,
+    Rectangle, Shell, Size, Widget,
 };
 
 use std::hash::Hash;
@@ -191,7 +191,7 @@ where
         cursor_position: Point,
         _renderer: &Renderer,
         _clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         let is_dragging = self.state.is_dragging;
 
@@ -220,7 +220,7 @@ where
             };
 
             if (self.value.into() - new_value.into()).abs() > f64::EPSILON {
-                messages.push((self.on_change)(new_value));
+                shell.publish((self.on_change)(new_value));
 
                 self.value = new_value;
             }
@@ -241,7 +241,7 @@ where
             | Event::Touch(touch::Event::FingerLost { .. }) => {
                 if is_dragging {
                     if let Some(on_release) = self.on_release.clone() {
-                        messages.push(on_release);
+                        shell.publish(on_release);
                     }
                     self.state.is_dragging = false;
 
diff --git a/native/src/widget/text_input.rs b/native/src/widget/text_input.rs
index 40c6c573..5e1726db 100644
--- a/native/src/widget/text_input.rs
+++ b/native/src/widget/text_input.rs
@@ -21,7 +21,7 @@ use crate::text::{self, Text};
 use crate::touch;
 use crate::{
     Clipboard, Color, Element, Hasher, Layout, Length, Padding, Point,
-    Rectangle, Size, Vector, Widget,
+    Rectangle, Shell, Size, Vector, Widget,
 };
 
 use std::u32;
@@ -384,7 +384,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         match event {
             Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
@@ -509,7 +509,7 @@ where
                 editor.insert(c);
 
                 let message = (self.on_change)(editor.contents());
-                messages.push(message);
+                shell.publish(message);
 
                 return event::Status::Captured;
             }
@@ -521,7 +521,7 @@ where
                 match key_code {
                     keyboard::KeyCode::Enter => {
                         if let Some(on_submit) = self.on_submit.clone() {
-                            messages.push(on_submit);
+                            shell.publish(on_submit);
                         }
                     }
                     keyboard::KeyCode::Backspace => {
@@ -551,7 +551,7 @@ where
                         editor.backspace();
 
                         let message = (self.on_change)(editor.contents());
-                        messages.push(message);
+                        shell.publish(message);
                     }
                     keyboard::KeyCode::Delete => {
                         if platform::is_jump_modifier_pressed(modifiers)
@@ -582,7 +582,7 @@ where
                         editor.delete();
 
                         let message = (self.on_change)(editor.contents());
-                        messages.push(message);
+                        shell.publish(message);
                     }
                     keyboard::KeyCode::Left => {
                         if platform::is_jump_modifier_pressed(modifiers)
@@ -674,7 +674,7 @@ where
                         editor.delete();
 
                         let message = (self.on_change)(editor.contents());
-                        messages.push(message);
+                        shell.publish(message);
                     }
                     keyboard::KeyCode::V => {
                         if self.state.keyboard_modifiers.command() {
@@ -700,7 +700,7 @@ where
                             editor.paste(content.clone());
 
                             let message = (self.on_change)(editor.contents());
-                            messages.push(message);
+                            shell.publish(message);
 
                             self.state.is_pasting = Some(content);
                         } else {
diff --git a/native/src/widget/toggler.rs b/native/src/widget/toggler.rs
index 2dcc3ffe..6cecc7e1 100644
--- a/native/src/widget/toggler.rs
+++ b/native/src/widget/toggler.rs
@@ -10,7 +10,7 @@ use crate::text;
 use crate::widget::{Row, Text};
 use crate::{
     Alignment, Clipboard, Element, Event, Hasher, Layout, Length, Point,
-    Rectangle, Widget,
+    Rectangle, Shell, Widget,
 };
 
 pub use iced_style::toggler::{Style, StyleSheet};
@@ -173,14 +173,14 @@ where
         cursor_position: Point,
         _renderer: &Renderer,
         _clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         match event {
             Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left)) => {
                 let mouse_over = layout.bounds().contains(cursor_position);
 
                 if mouse_over {
-                    messages.push((self.on_toggle)(!self.is_active));
+                    shell.publish((self.on_toggle)(!self.is_active));
 
                     event::Status::Captured
                 } else {
diff --git a/native/src/widget/tooltip.rs b/native/src/widget/tooltip.rs
index c35005e0..79a57824 100644
--- a/native/src/widget/tooltip.rs
+++ b/native/src/widget/tooltip.rs
@@ -11,8 +11,8 @@ use crate::text;
 use crate::widget::container;
 use crate::widget::text::Text;
 use crate::{
-    Clipboard, Element, Event, Hasher, Layout, Length, Padding, Point, Size,
-    Vector, Widget,
+    Clipboard, Element, Event, Hasher, Layout, Length, Padding, Point, Shell,
+    Size, Vector, Widget,
 };
 
 /// An element to display a widget over another.
@@ -130,7 +130,7 @@ where
         cursor_position: Point,
         renderer: &Renderer,
         clipboard: &mut dyn Clipboard,
-        messages: &mut Vec<Message>,
+        shell: &mut Shell<'_, Message>,
     ) -> event::Status {
         self.content.widget.on_event(
             event,
@@ -138,7 +138,7 @@ where
             cursor_position,
             renderer,
             clipboard,
-            messages,
+            shell,
         )
     }