Add the activity handler

lib/src/rendering/sliver_sticky_header.dart

@@ -2,6 +2,7 @@ import 'dart:math' as math;
 
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
+import 'package:flutter/scheduler.dart';
 import 'package:flutter_sticky_header/flutter_sticky_header.dart';
 import 'package:value_layout_builder/value_layout_builder.dart';
 
@@ -16,13 +17,17 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
     bool overlapsContent: false,
     bool sticky: true,
     StickyHeaderController? controller,
+    this.activityHandler,
   })  : _overlapsContent = overlapsContent,
         _sticky = sticky,
         _controller = controller {
     this.header = header as RenderBox?;
     this.child = child;
   }
 
+  SliverStickyHeaderActivityHandler? activityHandler;
+  SliverStickyHeaderActivity? _lastReportedActivity;
+
   SliverStickyHeaderState? _oldState;
   double? _headerExtent;
   late bool _isPinned;
@@ -261,6 +266,9 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
         controller?.stickyHeaderScrollOffset =
             constraints.precedingScrollExtent;
       }
+
+      _tryNotifyActivity(headerScrollRatio);
+
       // second layout if scroll percentage changed and header is a
       // RenderStickyHeaderLayoutBuilder.
       if (header is RenderConstrainedLayoutBuilder<
@@ -300,6 +308,32 @@ class RenderSliverStickyHeader extends RenderSliver with RenderSliverHelpers {
     }
   }
 
+  void _tryNotifyActivity(double headerScrollRatio) {
+    final SliverStickyHeaderActivity location;
+    if (_isPinned) {
+      if (headerScrollRatio >= 1) {
+        location = SliverStickyHeaderActivity.pushed;
+      } else if (headerScrollRatio > 0) {
+        location = SliverStickyHeaderActivity.settling;
+      } else {
+        location = SliverStickyHeaderActivity.pinned;
+      }
+    } else {
+      location = SliverStickyHeaderActivity.unpinned;
+    }
+
+    if (activityHandler != null &&
+        _lastReportedActivity != null &&
+        location != _lastReportedActivity) {
+      WidgetsBinding.instance.scheduleTask(
+        () => activityHandler?.call(location),
+        Priority.touch,
+      );
+    }
+
+    _lastReportedActivity = location;
+  }
+
   @override
   bool hitTestChildren(SliverHitTestResult result,
       {required double mainAxisPosition, required double crossAxisPosition}) {

lib/src/widgets/sliver_sticky_header.dart

@@ -134,6 +134,9 @@ class SliverStickyHeaderState {
   }
 }
 
+typedef SliverStickyHeaderActivityHandler = void Function(
+    SliverStickyHeaderActivity activity);
+
 enum SliverStickyHeaderActivity {
   pushed,
   unpinned,
@@ -162,6 +165,7 @@ class SliverStickyHeader extends RenderObjectWidget {
     this.overlapsContent: false,
     this.sticky = true,
     this.controller,
+    this.activityHandler,
   }) : super(key: key);
 
   /// Creates a widget that builds the header of a [SliverStickyHeader]
@@ -178,6 +182,7 @@ class SliverStickyHeader extends RenderObjectWidget {
     bool overlapsContent: false,
     bool sticky = true,
     StickyHeaderController? controller,
+    SliverStickyHeaderActivityHandler? activityHandler,
   }) : this(
           key: key,
           header: ValueLayoutBuilder<SliverStickyHeaderState>(
@@ -188,6 +193,7 @@ class SliverStickyHeader extends RenderObjectWidget {
           overlapsContent: overlapsContent,
           sticky: sticky,
           controller: controller,
+          activityHandler: activityHandler,
         );
 
   /// The header to display before the sliver.
@@ -210,12 +216,15 @@ class SliverStickyHeader extends RenderObjectWidget {
   /// will be used.
   final StickyHeaderController? controller;
 
+  final SliverStickyHeaderActivityHandler? activityHandler;
+
   @override
   RenderSliverStickyHeader createRenderObject(BuildContext context) {
     return RenderSliverStickyHeader(
       overlapsContent: overlapsContent,
       sticky: sticky,
       controller: controller ?? DefaultStickyHeaderController.of(context),
+      activityHandler: activityHandler,
     );
   }
 
@@ -231,7 +240,8 @@ class SliverStickyHeader extends RenderObjectWidget {
     renderObject
       ..overlapsContent = overlapsContent
       ..sticky = sticky
-      ..controller = controller ?? DefaultStickyHeaderController.of(context);
+      ..controller = controller ?? DefaultStickyHeaderController.of(context)
+      ..activityHandler = activityHandler;
   }
 }