feat: adding has mounted to component (#1418)

* feat: adding has mounted to component

* feat: pr suggestions

* feat: improving hasMounted

* feat: renaming hasMounted to mounted

* feat: pr suggestion

packages/flame/lib/src/components/component.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:collection';
 
 import 'package:flutter/painting.dart';
@@ -53,6 +54,8 @@ class Component {
  bool get hasChildren => _children?.isNotEmpty ?? false;
  ComponentSet? _children;
 
+ Completer<void>? _mountCompleter;
+
  @protected
  _LifecycleManager get lifecycle => _lifecycleManager ??= _LifecycleManager();
  _LifecycleManager? _lifecycleManager;
@@ -203,6 +206,17 @@ class Component {
  /// ```
  void onMount() {}
 
+ /// A future that will complete once the component is mounted on its parent
+ Future<void> get mounted {
+ if (isMounted) {
+ return Future.value();
+ }
+
+ _mountCompleter ??= Completer<void>();
+
+ return _mountCompleter!.future;
+ }
+
  /// This method is called periodically by the game engine to request that your
  /// component updates itself.
  ///
@@ -258,6 +272,7 @@ class Component {
  /// Changes the current parent for another parent and prepares the tree under
  /// the new root.
  void changeParent(Component component) {
+ _mountCompleter = null;
  parent?.remove(this);
  nextParent = component;
  }
@@ -403,6 +418,8 @@ class Component {
  if (existingChild || _state == LifecycleState.removed) {
  onGameResize(findGame()!.canvasSize);
  }
+ _mountCompleter?.complete();
+ _mountCompleter = null;
  onMount();
  _state = LifecycleState.mounted;
  if (!existingChild) {

packages/flame/test/components/component_lifecycle_test.dart

@@ -47,6 +47,52 @@ void main() {
  );
  });
 
+ flameGame.test('component mounted completes', (game) async {
+ final component = _MyComponent();
+ await game.add(component);
+ final mounted = component.mounted;
+
+ await game.ready();
+
+ return expectLater(mounted, completes);
+ });
+
+ flameGame.test(
+ 'component mounted completes even after the '
+ 'component is already mounted',
+ (game) async {
+ final component = _MyComponent();
+ await game.add(component);
+ await game.ready();
+
+ final mounted = component.mounted;
+
+ return expectLater(mounted, completes);
+ },
+ );
+
+ flameGame.test(
+ 'component mounted completes when changing parent',
+ (game) async {
+ final parent = _MyComponent('parent');
+ final child = _MyComponent('child');
+ parent.add(child);
+ game.add(parent);
+
+ var mounted = child.mounted;
+ await game.ready();
+
+ await expectLater(mounted, completes);
+
+ child.changeParent(game);
+ mounted = child.mounted;
+ game.update(0);
+ await game.ready();
+
+ await expectLater(mounted, completes);
+ },
+ );
+
  // Obsolete scenario, when we used to have a separate "prepare" stage
  flameGame.test('parent prepares the component', (game) async {
  final parent = _MyComponent('parent');