`next_gen_ui_demo`: Dispose of old `AnimationController`s (#1852)

next_gen_ui_demo/lib/main.dart

@@ -74,7 +74,17 @@ List<
 typedef ColorCallback = void Function(Color colorSchemeSeed);
 
 class _NextGenAppState extends State<NextGenApp> {
-  int step = 0;
+  int _step = 0;
+  int get step => _step;
+  set step(int i) {
+    _step = switch (i) {
+      (int a) when a < 0 => 0,
+      (int a) when a >= steps.length => steps.length - 1,
+      _ => i,
+    };
+    debugPrint('Step ${step + 1} of ${steps.length}');
+  }
+
   Color? colorSchemeSeed;
 
   @override
@@ -107,8 +117,7 @@ class _NextGenAppState extends State<NextGenApp> {
                 child: const Icon(Icons.arrow_back),
                 onPressed: () {
                   setState(() {
-                    if (step > 0) step--;
-                    debugPrint('Step = $step');
+                    step--;
                   });
                 },
               ),
@@ -123,8 +132,7 @@ class _NextGenAppState extends State<NextGenApp> {
                 child: const Icon(Icons.arrow_forward),
                 onPressed: () {
                   setState(() {
-                    if (step + 1 < steps.length) step++;
-                    debugPrint('Step = $step');
+                    step++;
                   });
                 },
               ),
@@ -140,7 +148,6 @@ class _NextGenAppState extends State<NextGenApp> {
                     onPressed: () {
                       setState(() {
                         step = 0;
-                        debugPrint('Step = $step');
                       });
                     },
                   ),

next_gen_ui_demo/lib/title_screen_4c/title_screen_ui.dart

@@ -255,7 +255,15 @@ class _StartBtnState extends State<_StartBtn> {
               ),
             ],
           )
-              .animate(autoPlay: false, onInit: (c) => _btnAnim = c)
+              .animate(
+                autoPlay: false,
+                onInit: (c) {
+                  if (_btnAnim != null && _btnAnim != c) {
+                    _btnAnim?.dispose();
+                  }
+                  _btnAnim = c;
+                },
+              )
               .shimmer(duration: .7.seconds, color: Colors.black),
         )
             .animate()

next_gen_ui_demo/lib/title_screen_4d/title_screen_ui.dart

@@ -261,7 +261,15 @@ class _StartBtnState extends State<_StartBtn> {
               ),
             ],
           )
-              .animate(autoPlay: false, onInit: (c) => _btnAnim = c)
+              .animate(
+                autoPlay: false,
+                onInit: (c) {
+                  if (_btnAnim != null && _btnAnim != c) {
+                    _btnAnim?.dispose();
+                  }
+                  _btnAnim = c;
+                },
+              )
               .shimmer(duration: .7.seconds, color: Colors.black),
         )
             .animate()

next_gen_ui_demo/lib/title_screen_4e/title_screen_ui.dart

@@ -261,7 +261,15 @@ class _StartBtnState extends State<_StartBtn> {
               ),
             ],
           )
-              .animate(autoPlay: false, onInit: (c) => _btnAnim = c)
+              .animate(
+                autoPlay: false,
+                onInit: (c) {
+                  if (_btnAnim != null && _btnAnim != c) {
+                    _btnAnim?.dispose();
+                  }
+                  _btnAnim = c;
+                },
+              )
               .shimmer(duration: .7.seconds, color: Colors.black),
         )
             .animate()

next_gen_ui_demo/lib/title_screen_5a/title_screen_ui.dart

@@ -287,7 +287,15 @@ class _StartBtnState extends State<_StartBtn> {
               ),
             ],
           )
-              .animate(autoPlay: false, onInit: (c) => _btnAnim = c)
+              .animate(
+                autoPlay: false,
+                onInit: (c) {
+                  if (_btnAnim != null && _btnAnim != c) {
+                    _btnAnim?.dispose();
+                  }
+                  _btnAnim = c;
+                },
+              )
               .shimmer(duration: .7.seconds, color: Colors.black),
         )
             .animate()

next_gen_ui_demo/lib/title_screen_5b/title_screen_ui.dart

@@ -289,7 +289,15 @@ class _StartBtnState extends State<_StartBtn> {
               ),
             ],
           )
-              .animate(autoPlay: false, onInit: (c) => _btnAnim = c)
+              .animate(
+                autoPlay: false,
+                onInit: (c) {
+                  if (_btnAnim != null && _btnAnim != c) {
+                    _btnAnim?.dispose();
+                  }
+                  _btnAnim = c;
+                },
+              )
               .shimmer(duration: .7.seconds, color: Colors.black),
         )
             .animate()

next_gen_ui_demo/lib/title_screen_6/title_screen_ui.dart

@@ -289,7 +289,15 @@ class _StartBtnState extends State<_StartBtn> {
               ),
             ],
           )
-              .animate(autoPlay: false, onInit: (c) => _btnAnim = c)
+              .animate(
+                autoPlay: false,
+                onInit: (c) {
+                  if (_btnAnim != null && _btnAnim != c) {
+                    _btnAnim?.dispose();
+                  }
+                  _btnAnim = c;
+                },
+              )
               .shimmer(duration: .7.seconds, color: Colors.black),
         )
             .animate()