refactor: Make GestureDetectorBuilder and detector/callback registering more resilient (#3900)

Make GestureDetectorBuilder and detector/callback registering more
resilient wrt to multiple registrations (callbacks that use the same
detector).

This extracts a base class to dispatchers to share code and remove
reundancies.
It also makes the code on *Callbacks themselves trivial, and accounts
for duplication.
Before different callbacks could duplicate dispatchers. Now we properly
guarantee dispatchers are singleton while allowing callbacks to require
and use the same dispatcher. This is important for tertiary callbacks
which will use the same underlying dispatcher as secondary.

Author: luanpotter

packages/flame/lib/src/events/component_mixins/double_tap_callbacks.dart

@@ -10,6 +10,8 @@ import 'package:flame/events.dart';
 /// At present, flutter detects only one double-tap events simultaneously.
 /// This means that if you're double-tapping two [DoubleTapCallbacks] located
 /// far away from each other, only one callback will be fired (or none).
+///
+/// This callback uses [DoubleTapDispatcher] to route events.
 mixin DoubleTapCallbacks on Component {
   /// This triggers when the pointer stops contacting the device after the
   /// second tap.
@@ -25,11 +27,6 @@ mixin DoubleTapCallbacks on Component {
   @override
   void onMount() {
     super.onMount();
-    final game = findRootGame()!;
-    if (game.findByKey(const DoubleTapDispatcherKey()) == null) {
-      final dispatcher = DoubleTapDispatcher();
-      game.registerKey(const DoubleTapDispatcherKey(), dispatcher);
-      game.add(dispatcher);
-    }
+    DoubleTapDispatcher.addDispatcher(this);
   }
 }

packages/flame/lib/src/events/component_mixins/drag_callbacks.dart

@@ -10,6 +10,8 @@ import 'package:meta/meta.dart';
 /// the component.
 ///
 /// This mixin is the replacement of the Draggable mixin.
+///
+/// This callback uses [MultiDragDispatcher] to route events.
 mixin DragCallbacks on Component {
   bool _isDragged = false;
 
@@ -61,11 +63,6 @@ mixin DragCallbacks on Component {
   @mustCallSuper
   void onMount() {
     super.onMount();
-    final game = findRootGame()!;
-    if (game.findByKey(const MultiDragDispatcherKey()) == null) {
-      final dispatcher = MultiDragDispatcher();
-      game.registerKey(const MultiDragDispatcherKey(), dispatcher);
-      game.add(dispatcher);
-    }
+    MultiDragDispatcher.addDispatcher(this);
   }
 }

packages/flame/lib/src/events/component_mixins/hover_callbacks.dart

@@ -11,6 +11,8 @@ import 'package:meta/meta.dart';
 /// component.
 ///
 /// This mixin is the replacement of the Hoverable mixin.
+///
+/// This callback uses [PointerMoveDispatcher] to route events.
 mixin HoverCallbacks on Component implements PointerMoveCallbacks {
   bool _isHovered = false;
 
@@ -56,6 +58,6 @@ mixin HoverCallbacks on Component implements PointerMoveCallbacks {
   @mustCallSuper
   void onMount() {
     super.onMount();
-    PointerMoveCallbacks.onMountHandler(this);
+    PointerMoveDispatcher.addDispatcher(this);
   }
 }

packages/flame/lib/src/events/component_mixins/long_press_callbacks.dart

@@ -19,6 +19,8 @@ import 'package:flutter/foundation.dart';
 ///   long press.
 /// - [onLongPressEnd]: called when the pointer is lifted after a long press.
 /// - [onLongPressCancel]: called if the gesture is cancelled before completion.
+///
+/// This callback uses [LongPressDispatcher] to route events.
 mixin LongPressCallbacks on Component {
   bool _isLongPressing = false;
 
@@ -46,11 +48,6 @@ mixin LongPressCallbacks on Component {
   @mustCallSuper
   void onMount() {
     super.onMount();
-    final game = findRootGame()!;
-    if (game.findByKey(const LongPressDispatcherKey()) == null) {
-      final dispatcher = LongPressDispatcher();
-      game.registerKey(const LongPressDispatcherKey(), dispatcher);
-      game.add(dispatcher);
-    }
+    LongPressDispatcher.addDispatcher(this);
   }
 }

packages/flame/lib/src/events/component_mixins/pointer_move_callbacks.dart

@@ -4,6 +4,8 @@ import 'package:meta/meta.dart';
 
 /// This mixin can be added to a [Component] allowing it to receive
 /// pointer movement events.
+///
+/// This callback uses [PointerMoveDispatcher] to route events.
 mixin PointerMoveCallbacks on Component {
   void onPointerMove(PointerMoveEvent event) {}
 
@@ -13,16 +15,6 @@ mixin PointerMoveCallbacks on Component {
   @mustCallSuper
   void onMount() {
     super.onMount();
-    onMountHandler(this);
-  }
-
-  static void onMountHandler(PointerMoveCallbacks instance) {
-    final game = instance.findRootGame()!;
-    const key = MouseMoveDispatcherKey();
-    if (game.findByKey(key) == null) {
-      final dispatcher = PointerMoveDispatcher();
-      game.registerKey(key, dispatcher);
-      game.add(dispatcher);
-    }
+    PointerMoveDispatcher.addDispatcher(this);
   }
 }

packages/flame/lib/src/events/component_mixins/scale_callbacks.dart

@@ -3,6 +3,7 @@ import 'package:flame/events.dart';
 import 'package:flame/src/events/flame_game_mixins/scale_dispatcher.dart';
 import 'package:flutter/foundation.dart';
 
+/// This callback uses [ScaleDispatcher] to route events.
 mixin ScaleCallbacks on Component {
   bool _isScaling = false;
 
@@ -25,11 +26,6 @@ mixin ScaleCallbacks on Component {
   @mustCallSuper
   void onMount() {
     super.onMount();
-    final game = findRootGame()!;
-    if (game.findByKey(const ScaleDispatcherKey()) == null) {
-      final dispatcher = ScaleDispatcher();
-      game.registerKey(const ScaleDispatcherKey(), dispatcher);
-      game.add(dispatcher);
-    }
+    ScaleDispatcher.addDispatcher(this);
   }
 }

packages/flame/lib/src/events/component_mixins/scroll_callbacks.dart

@@ -5,23 +5,15 @@ import 'package:meta/meta.dart';
 
 /// This mixin can be added to a [Component] allowing it to receive
 /// pointer scroll (mouse wheel) events.
+///
+/// This callback uses [ScrollDispatcher] to route events.
 mixin ScrollCallbacks on Component {
   void onScroll(ScrollEvent event) {}
 
   @override
   @mustCallSuper
   void onMount() {
     super.onMount();
-    onMountHandler(this);
-  }
-
-  static void onMountHandler(ScrollCallbacks instance) {
-    final game = instance.findRootGame()!;
-    const key = ScrollDispatcherKey();
-    if (game.findByKey(key) == null) {
-      final dispatcher = ScrollDispatcher();
-      game.registerKey(key, dispatcher);
-      game.add(dispatcher);
-    }
+    ScrollDispatcher.addDispatcher(this);
   }
 }

packages/flame/lib/src/events/component_mixins/secondary_tap_callbacks.dart

@@ -11,6 +11,8 @@ import 'package:meta/meta.dart';
 ///
 /// Note that FlameGame _is_ a [Component] and does implement
 /// [containsLocalPoint]; so this can be used at the game level.
+///
+/// This callback uses [SecondaryTapDispatcher] to route events.
 mixin SecondaryTapCallbacks on Component {
   void onSecondaryTapDown(SecondaryTapDownEvent event) {}
   void onSecondaryTapUp(SecondaryTapUpEvent event) {}
@@ -20,11 +22,6 @@ mixin SecondaryTapCallbacks on Component {
   @mustCallSuper
   void onMount() {
     super.onMount();
-    final game = findRootGame()!;
-    if (game.findByKey(const SecondaryTapDispatcherKey()) == null) {
-      final dispatcher = SecondaryTapDispatcher();
-      game.registerKey(const SecondaryTapDispatcherKey(), dispatcher);
-      game.add(dispatcher);
-    }
+    SecondaryTapDispatcher.addDispatcher(this);
   }
 }

packages/flame/lib/src/events/component_mixins/tap_callbacks.dart

@@ -10,6 +10,8 @@ import 'package:meta/meta.dart';
 ///
 /// Note that FlameGame _is_ a [Component] and does implement
 /// [containsLocalPoint]; so this can be used at the game level.
+///
+/// This callback uses [MultiTapDispatcher] to route events.
 mixin TapCallbacks on Component {
   void onTapDown(TapDownEvent event) {}
   void onLongTapDown(TapDownEvent event) {}
@@ -20,11 +22,6 @@ mixin TapCallbacks on Component {
   @mustCallSuper
   void onMount() {
     super.onMount();
-    final game = findRootGame()!;
-    if (game.findByKey(const MultiTapDispatcherKey()) == null) {
-      final dispatcher = MultiTapDispatcher();
-      game.registerKey(const MultiTapDispatcherKey(), dispatcher);
-      game.add(dispatcher);
-    }
+    MultiTapDispatcher.addDispatcher(this);
   }
 }

packages/flame/lib/src/events/flame_game_mixins/dispatcher.dart

@@ -0,0 +1,23 @@
+import 'package:flame/components.dart';
+import 'package:flame/src/game/flame_game.dart';
+
+abstract class Dispatcher<G extends FlameGame> extends Component
+    with HasGameReference<G> {
+  static void addDispatcher<T extends Component>(
+    Component component,
+    ComponentKey key,
+    T Function() create,
+  ) {
+    final game = component.findRootGame()!;
+    if (game.findByKey(key) != null) {
+      return;
+    }
+    final dispatcher = create();
+    game.registerKey(key, dispatcher);
+    game.add(dispatcher);
+  }
+
+  static void removeDispatcher(FlameGame game, ComponentKey key) {
+    game.unregisterKey(key);
+  }
+}