diff --git a/src/dynamic.rs b/src/dynamic.rs
index 9d1f934..e042b56 100644
--- a/src/dynamic.rs
+++ b/src/dynamic.rs
@@ -31,12 +31,7 @@ impl<T> Dynamic<T> {
     }
 
     pub fn map_mut<R>(&self, map: impl FnOnce(&mut T) -> R) -> R {
-        let mut state = self.state();
-        state.wrapped.generation = state.wrapped.generation.wrapping_add(1);
-        let result = map(&mut state.wrapped.value);
-        drop(state);
-        self.0.sync.notify_all();
-        result
+        self.0.map_mut(map)
     }
 
     pub fn for_each<F>(&self, mut map: F)
@@ -72,7 +67,7 @@ impl<T> Dynamic<T> {
 
     #[must_use]
     pub fn replace(&self, new_value: T) -> T {
-        self.0.replace(new_value).value
+        self.0.map_mut(|value| std::mem::replace(value, new_value))
     }
 
     pub fn set(&self, new_value: T) {
@@ -150,18 +145,13 @@ impl<T> DynamicData<T> {
     }
 
     #[must_use]
-    pub fn replace(&self, new_value: T) -> GenerationalValue<T> {
+    pub fn map_mut<R>(&self, map: impl FnOnce(&mut T) -> R) -> R {
         let mut state = self.state();
         let old = {
             let state = &mut *state;
             let generation = state.wrapped.generation.wrapping_add(1);
-            let old = std::mem::replace(
-                &mut state.wrapped,
-                GenerationalValue {
-                    value: new_value,
-                    generation,
-                },
-            );
+            let result = map(&mut state.wrapped.value);
+            state.wrapped.generation = generation;
 
             for callback in &mut state.callbacks {
                 callback.update(&state.wrapped);
@@ -169,7 +159,7 @@ impl<T> DynamicData<T> {
             for window in state.windows.drain(..) {
                 let _result = window.send(WindowCommand::Redraw);
             }
-            old
+            result
         };
         drop(state);
 
diff --git a/src/widget.rs b/src/widget.rs
index 9305648..4a35a91 100644
--- a/src/widget.rs
+++ b/src/widget.rs
@@ -11,7 +11,7 @@ use kludgine::app::winit::event::{
 use kludgine::figures::units::{Px, UPx};
 use kludgine::figures::{Point, Rect, Size};
 
-use crate::context::{EventContext, GraphicsContext};
+use crate::context::{EventContext, GraphicsContext, WidgetContext};
 use crate::dynamic::Dynamic;
 use crate::styles::{Component, Group, Styles};
 use crate::tree::{Tree, WidgetId};
@@ -246,6 +246,12 @@ impl<T> Value<T> {
             Value::Dynamic(value) => Some(value.generation()),
         }
     }
+
+    pub fn redraw_when_changed(&self, context: &WidgetContext<'_, '_>) {
+        if let Value::Dynamic(dynamic) = self {
+            context.redraw_when_changed(dynamic);
+        }
+    }
 }
 
 pub trait IntoValue<T> {
@@ -276,9 +282,9 @@ impl<T> IntoValue<T> for Value<T> {
     }
 }
 
-pub struct Callback<T>(Box<dyn CallbackFunction<T>>);
+pub struct Callback<T = (), R = ()>(Box<dyn CallbackFunction<T, R>>);
 
-impl<T> Debug for Callback<T> {
+impl<T, R> Debug for Callback<T, R> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         f.debug_tuple("Callback")
             .field(&(self as *const Self))
@@ -286,28 +292,29 @@ impl<T> Debug for Callback<T> {
     }
 }
 
-impl<T> Callback<T> {
+impl<T, R> Callback<T, R> {
     pub fn new<F>(function: F) -> Self
     where
-        F: FnMut(T) + Send + UnwindSafe + 'static,
+        F: FnMut(T) -> R + Send + UnwindSafe + 'static,
     {
         Self(Box::new(function))
     }
 
-    pub fn invoke(&mut self, value: T) {
-        self.0.invoke(value);
+    pub fn invoke(&mut self, value: T) -> R {
+        self.0.invoke(value)
     }
 }
 
-trait CallbackFunction<T>: Send + UnwindSafe {
-    fn invoke(&mut self, value: T);
+trait CallbackFunction<T, R>: Send + UnwindSafe {
+    fn invoke(&mut self, value: T) -> R;
 }
-impl<T, F> CallbackFunction<T> for F
+
+impl<T, R, F> CallbackFunction<T, R> for F
 where
-    F: FnMut(T) + Send + UnwindSafe,
+    F: FnMut(T) -> R + Send + UnwindSafe,
 {
-    fn invoke(&mut self, value: T) {
-        self(value);
+    fn invoke(&mut self, value: T) -> R {
+        self(value)
     }
 }
 
diff --git a/src/widgets/button.rs b/src/widgets/button.rs
index cfc88a8..051e4e4 100644
--- a/src/widgets/button.rs
+++ b/src/widgets/button.rs
@@ -50,9 +50,7 @@ impl Button {
 impl Widget for Button {
     fn redraw(&mut self, context: &mut GraphicsContext<'_, '_, '_, '_, '_>) {
         let center = Point::from(context.graphics.size()) / 2;
-        if let Value::Dynamic(label) = &self.label {
-            context.redraw_when_changed(label);
-        }
+        self.label.redraw_when_changed(context);
 
         let styles = context.query_style(&[
             &TextColor,
diff --git a/src/widgets/label.rs b/src/widgets/label.rs
index 3d47d14..a13c492 100644
--- a/src/widgets/label.rs
+++ b/src/widgets/label.rs
@@ -22,10 +22,9 @@ impl Label {
 
 impl Widget for Label {
     fn redraw(&mut self, context: &mut GraphicsContext<'_, '_, '_, '_, '_>) {
+        self.contents.redraw_when_changed(context);
+
         let center = Point::from(context.graphics.size()) / 2;
-        if let Value::Dynamic(contents) = &mut self.contents {
-            context.redraw_when_changed(contents);
-        }
         let styles = context.query_style(&[&TextColor]);
         let width = context.graphics.size().width;
         self.contents.map(|contents| {