Provide widgets IDs to Operation::container

native/src/widget/container.rs

@@ -5,7 +5,7 @@ use crate::layout;
 use crate::mouse;
 use crate::overlay;
 use crate::renderer;
-use crate::widget::{Operation, Tree};
+use crate::widget::{self, Operation, Tree};
 use crate::{
     Background, Clipboard, Color, Element, Layout, Length, Padding, Point,
     Rectangle, Shell, Widget,
@@ -24,6 +24,7 @@ where
     Renderer: crate::Renderer,
     Renderer::Theme: StyleSheet,
 {
+    id: Option<Id>,
     padding: Padding,
     width: Length,
     height: Length,
@@ -46,6 +47,7 @@ where
         T: Into<Element<'a, Message, Renderer>>,
     {
         Container {
+            id: None,
             padding: Padding::ZERO,
             width: Length::Shrink,
             height: Length::Shrink,
@@ -58,6 +60,12 @@ where
         }
     }
 
+    /// Sets the [`Id`] of the [`Container`].
+    pub fn id(mut self, id: Id) -> Self {
+        self.id = Some(id);
+        self
+    }
+
     /// Sets the [`Padding`] of the [`Container`].
     pub fn padding<P: Into<Padding>>(mut self, padding: P) -> Self {
         self.padding = padding.into();
@@ -172,14 +180,17 @@ where
         renderer: &Renderer,
         operation: &mut dyn Operation<Message>,
     ) {
-        operation.container(None, &mut |operation| {
-            self.content.as_widget().operate(
-                &mut tree.children[0],
-                layout.children().next().unwrap(),
-                renderer,
-                operation,
-            );
-        });
+        operation.container(
+            self.id.as_ref().map(|id| &id.0),
+            &mut |operation| {
+                self.content.as_widget().operate(
+                    &mut tree.children[0],
+                    layout.children().next().unwrap(),
+                    renderer,
+                    operation,
+                );
+            },
+        );
     }
 
     fn on_event(
@@ -333,3 +344,27 @@ pub fn draw_background<Renderer>(
         );
     }
 }
+
+/// The identifier of a [`Container`].
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct Id(widget::Id);
+
+impl Id {
+    /// Creates a custom [`Id`].
+    pub fn new(id: impl Into<std::borrow::Cow<'static, str>>) -> Self {
+        Self(widget::Id::new(id))
+    }
+
+    /// Creates a unique [`Id`].
+    ///
+    /// This function produces a different [`Id`] every time it is called.
+    pub fn unique() -> Self {
+        Self(widget::Id::unique())
+    }
+}
+
+impl From<Id> for widget::Id {
+    fn from(id: Id) -> Self {
+        id.0
+    }
+}

native/src/widget/scrollable.rs

@@ -208,14 +208,17 @@ where
 
         operation.scrollable(state, self.id.as_ref().map(|id| &id.0));
 
-        operation.container(None, &mut |operation| {
-            self.content.as_widget().operate(
-                &mut tree.children[0],
-                layout.children().next().unwrap(),
-                renderer,
-                operation,
-            );
-        });
+        operation.container(
+            self.id.as_ref().map(|id| &id.0),
+            &mut |operation| {
+                self.content.as_widget().operate(
+                    &mut tree.children[0],
+                    layout.children().next().unwrap(),
+                    renderer,
+                    operation,
+                );
+            },
+        );
     }
 
     fn on_event(