diff persistent state of widgets with an id based that id

widget/src/scrollable.rs

@@ -381,7 +381,7 @@ where
     }
 
     fn state(&self) -> tree::State {
-        tree::State::new(State::new())
+        tree::State::new(State::new(self.id.clone()))
     }
 
     fn diff(&mut self, tree: &mut Tree) {
@@ -396,6 +396,10 @@ where
         if self.direction.vertical().is_none() {
             self.height = self.height.enclose(size.height);
         }
+
+        if tree.state.downcast_mut::<State>().last_id != self.id {
+            tree.state = self.state();
+        }
     }
 
     fn size(&self) -> Size<Length> {
@@ -1489,14 +1493,15 @@ fn notify_viewport<Message>(
     true
 }
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone)]
 struct State {
     offset_y: Offset,
     offset_x: Offset,
     interaction: Interaction,
     keyboard_modifiers: keyboard::Modifiers,
     last_notified: Option<Viewport>,
     last_scrolled: Option<Instant>,
+    last_id: Option<widget::Id>,
     is_scrollbar_visible: bool,
 }
 
@@ -1513,20 +1518,6 @@ enum Interaction {
     },
 }
 
-impl Default for State {
-    fn default() -> Self {
-        Self {
-            offset_y: Offset::Absolute(0.0),
-            offset_x: Offset::Absolute(0.0),
-            interaction: Interaction::None,
-            keyboard_modifiers: keyboard::Modifiers::default(),
-            last_notified: None,
-            last_scrolled: None,
-            is_scrollbar_visible: true,
-        }
-    }
-}
-
 impl operation::Scrollable for State {
     fn snap_to(&mut self, offset: RelativeOffset<Option<f32>>) {
         State::snap_to(self, offset);
@@ -1623,8 +1614,17 @@ impl Viewport {
 }
 
 impl State {
-    fn new() -> Self {
-        State::default()
+    fn new(last_id: Option<widget::Id>) -> Self {
+        Self {
+            offset_y: Offset::Absolute(0.0),
+            offset_x: Offset::Absolute(0.0),
+            interaction: Interaction::None,
+            keyboard_modifiers: keyboard::Modifiers::default(),
+            last_notified: None,
+            last_scrolled: None,
+            last_id,
+            is_scrollbar_visible: true,
+        }
     }
 
     fn scroll(&mut self, delta: Vector<f32>, bounds: Rectangle, content_bounds: Rectangle) {

widget/src/text_editor.rs

@@ -496,6 +496,7 @@ pub struct State<Highlighter: text::Highlighter> {
     preedit: Option<input_method::Preedit>,
     last_click: Option<mouse::Click>,
     drag_click: Option<mouse::click::Kind>,
+    last_id: Option<widget::Id>,
     partial_scroll: f32,
     last_theme: RefCell<Option<String>>,
     highlighter: RefCell<Highlighter>,
@@ -568,6 +569,7 @@ where
             preedit: None,
             last_click: None,
             drag_click: None,
+            last_id: self.id.clone(),
             partial_scroll: 0.0,
             last_theme: RefCell::default(),
             highlighter: RefCell::new(Highlighter::new(&self.highlighter_settings)),
@@ -576,6 +578,12 @@ where
         })
     }
 
+    fn diff(&mut self, tree: &mut widget::Tree) {
+        if tree.state.downcast_mut::<State<Highlighter>>().last_id != self.id {
+            tree.state = self.state();
+        }
+    }
+
     fn size(&self) -> Size<Length> {
         Size {
             width: self.width,

widget/src/text_input.rs

@@ -600,7 +600,7 @@ where
     }
 
     fn state(&self) -> tree::State {
-        tree::State::new(State::<Renderer::Paragraph>::new())
+        tree::State::new(State::<Renderer::Paragraph>::new(self.id.clone()))
     }
 
     fn diff(&mut self, tree: &mut Tree) {
@@ -610,6 +610,10 @@ where
         if self.on_input.is_none() {
             state.is_pasting = None;
         }
+
+        if state.last_id != self.id {
+            tree.state = self.state();
+        }
     }
 
     fn size(&self) -> Size<Length> {
@@ -1371,6 +1375,7 @@ pub struct State<P: text::Paragraph> {
     last_click: Option<mouse::Click>,
     cursor: Cursor,
     keyboard_modifiers: keyboard::Modifiers,
+    last_id: Option<widget::Id>,
     // TODO: Add stateful horizontal scrolling offset
 }
 
@@ -1399,8 +1404,11 @@ enum Paste {
 
 impl<P: text::Paragraph> State<P> {
     /// Creates a new [`State`], representing an unfocused [`TextInput`].
-    pub fn new() -> Self {
-        Self::default()
+    pub fn new(last_id: Option<widget::Id>) -> Self {
+        Self {
+            last_id,
+            ..Self::default()
+        }
     }
 
     /// Returns whether the [`TextInput`] is currently focused or not.