API docs for typedefs. (#67003)

packages/flutter/lib/src/gestures/binding.dart

@@ -19,7 +19,7 @@ import 'pointer_router.dart';
 import 'pointer_signal_resolver.dart';
 import 'resampler.dart';
 
-typedef HandleSampleTimeChangedCallback = void Function();
+typedef _HandleSampleTimeChangedCallback = void Function();
 
 // Class that handles resampling of touch events for multiple pointer
 // devices.
@@ -48,7 +48,7 @@ class _Resampler {
   final HandleEventCallback _handlePointerEvent;
 
   // Callback used to handle sample time changes.
-  final HandleSampleTimeChangedCallback _handleSampleTimeChanged;
+  final _HandleSampleTimeChangedCallback _handleSampleTimeChanged;
 
   // Enqueue `events` for resampling or dispatch them directly if
   // not a touch event.

packages/flutter/lib/src/gestures/monodrag.dart

@@ -24,15 +24,18 @@ enum _DragState {
 /// The velocity at which the pointer was moving when it stopped contacting
 /// the screen is available in the `details`.
 ///
-/// See [DragGestureRecognizer.onEnd].
+/// Used by [DragGestureRecognizer.onEnd].
 typedef GestureDragEndCallback = void Function(DragEndDetails details);
 
 /// Signature for when the pointer that previously triggered a
 /// [GestureDragDownCallback] did not complete.
 ///
-/// See [DragGestureRecognizer.onCancel].
+/// Used by [DragGestureRecognizer.onCancel].
 typedef GestureDragCancelCallback = void Function();
 
+/// Signature for a function that builds a [VelocityTracker].
+///
+/// Used by [DragGestureRecognizer.velocityTrackerBuilder].
 typedef GestureVelocityTrackerBuilder = VelocityTracker Function(PointerEvent event);
 
 /// Recognizes movement.

packages/flutter/lib/src/gestures/resampler.dart

@@ -6,6 +6,8 @@ import 'dart:collection';
 
 import 'events.dart';
 
+/// A callback used by [PointerEventResampler.sample] and
+/// [PointerEventResampler.stop] to process a resampled `event`.
 typedef HandleEventCallback = void Function(PointerEvent event);
 
 /// Class for pointer event resampling.

packages/flutter/lib/src/material/bottom_sheet.dart

@@ -25,7 +25,14 @@ const Curve _modalBottomSheetCurve = decelerateEasing;
 const double _minFlingVelocity = 700.0;
 const double _closeProgressThreshold = 0.5;
 
+/// A callback for when the user begins dragging the bottom sheet.
+///
+/// Used by [BottomSheet.onDragStart].
 typedef BottomSheetDragStartHandler = void Function(DragStartDetails details);
+
+/// A callback for when the user stops dragging the bottom sheet.
+///
+/// Used by [BottomSheet.onDragEnd].
 typedef BottomSheetDragEndHandler = void Function(
   DragEndDetails details, {
   bool isClosing,

packages/flutter/lib/src/material/dropdown.dart

@@ -34,6 +34,9 @@ const EdgeInsets _kUnalignedButtonPadding = EdgeInsets.zero;
 const EdgeInsets _kAlignedMenuMargin = EdgeInsets.zero;
 const EdgeInsetsGeometry _kUnalignedMenuMargin = EdgeInsetsDirectional.only(start: 16.0, end: 24.0);
 
+/// A builder to customize dropdown buttons.
+///
+/// Used by [DropdownButton.selectedItemBuilder].
 typedef DropdownButtonBuilder = List<Widget> Function(BuildContext context);
 
 class _DropdownMenuPainter extends CustomPainter {

packages/flutter/lib/src/painting/debug.dart

@@ -31,6 +31,11 @@ typedef HttpClientProvider = HttpClient Function();
 /// This value is ignored in non-debug builds.
 HttpClientProvider? debugNetworkImageHttpClientProvider;
 
+/// Called when the framework is about to paint an [Image] to a [Canvas] with an
+/// [ImageSizeInfo] that contains the decoded size of the image as well as its
+/// output size.
+///
+/// See: [debugOnPaintImage].
 typedef PaintImageCallback = void Function(ImageSizeInfo);
 
 /// Tracks the bytes used by a [dart:ui.Image] compared to the bytes needed to

packages/flutter/lib/src/widgets/sliver.dart

@@ -213,6 +213,10 @@ class _SaltedValueKey extends ValueKey<Key>{
   const _SaltedValueKey(Key key): assert(key != null), super(key);
 }
 
+/// Called to find the new index of a child based on its key in case of
+/// reordering.
+///
+/// Used by [SliverChildBuilderDelegate.findChildIndexCallback].
 typedef ChildIndexGetter = int Function(Key key);
 
 /// A delegate that supplies children for slivers using a builder callback.