Introduction of SwitchEffect()

README.md

@@ -274,6 +274,8 @@ text.animate().fadeOut(300.ms) // fade out & then...
   .swap(builder: (_, child) => child.animate().fadeIn())
 ```
 
+See also SwitchEffect() for an alternative implementation of animations which switches between two or more childs. 
+
 ShaderEffect
 ----------------------------------------
 `ShaderEffect` makes it easy to apply animated GLSL fragment shaders to widgets.

lib/flutter_animate.dart

@@ -1,7 +1,8 @@
+export 'src/adapters/adapters.dart';
 export 'src/animate.dart';
 export 'src/animate_list.dart';
 export 'src/effect_list.dart';
-export 'src/flutter_animate.dart';
-export 'src/adapters/adapters.dart';
 export 'src/effects/effects.dart';
 export 'src/extensions/extensions.dart';
+export 'src/flutter_animate.dart';
+export 'src/switch_effect.dart';

lib/src/switch_effect.dart

@@ -0,0 +1,89 @@
+import 'package:flutter/cupertino.dart';
+import 'package:flutter_animate/flutter_animate.dart';
+
+/// A widget for implementing switch effects. When calling the first time the given [child] will be animated with [inEffects].
+/// When the widget is called again with a different child the [outEffects] of the previous widget instance will be applied to
+/// the [child] handled by the previous widget immediately following with the animation of the new child by using the
+/// [inEffects] of the new widget. Before switching the childs the optional callback method is triggered.
+class SwitchEffect extends StatefulWidget {
+  /// the child for this animation
+  final Widget child;
+
+  /// a list of effects to apply to the child when the child will be shown. Default is fadeIn()
+  final List<Effect>? inEffects;
+
+  /// a list of effects to apply to the child when the child should be replaced by another child. Default is fadeOut()
+  final List<Effect>? outEffects;
+
+  /// Callback function which will be triggered right after the outEffects are completed and before the new child will be swapped in for the inEffects
+  final void Function(BuildContext)? onSwap;
+
+  /// Callbak function which will be triggered after all effects are completed
+  final void Function(BuildContext)? onComplete;
+
+  const SwitchEffect(
+      {super.key,
+      required this.child,
+      this.inEffects,
+      this.outEffects,
+      this.onSwap,
+      this.onComplete});
+
+  @override
+  State<StatefulWidget> createState() {
+    return _SwitchEffectState();
+  }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+class _SwitchEffectState extends State {
+  @override
+  SwitchEffect get widget => super.widget as SwitchEffect;
+
+  /// when changing the child of the widget this field will be filled with the child of the previous widget.
+  Widget? _lastChild;
+
+  List<Effect>? _lastOutEffects;
+
+  @override
+  Widget build(BuildContext context) {
+    if (_lastChild != null) {
+      return Animate(
+        key: GlobalKey(),
+        effects: _lastOutEffects ?? EffectList().fadeOut(),
+        onComplete: (_) {
+          if (widget.onSwap != null) widget.onSwap!(context);
+        },
+        child: _lastChild!,
+      ).then().swap(
+          duration: 0.seconds,
+          delay: 0.seconds,
+          builder: (BuildContext context, _) => Animate(
+                effects: widget.inEffects ?? EffectList().fadeIn(),
+                onComplete: (_) {
+                  if (widget.onComplete != null) widget.onComplete!(context);
+                },
+                child: widget.child,
+              ));
+    }
+
+    return Animate(
+      key: GlobalKey(),
+      effects: widget.inEffects ?? EffectList().fadeIn(),
+      onComplete: (_) {
+        if (widget.onComplete != null) widget.onComplete!(context);
+      },
+      child: widget.child,
+    );
+  }
+
+  @override
+  void didUpdateWidget(covariant SwitchEffect oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (oldWidget.child != widget.child) {
+      _lastChild = oldWidget.child;
+      _lastOutEffects = oldWidget.outEffects;
+    }
+  }
+}