Updated the smiley TextButton example again (#144630)

Improved the smiley image TextButton example a little. Handling the case where the `Future.delayed` object that represents the button's one second long action is superseded by a second button press that triggers a new one-second action. This does complicate the example - just a little - but it's a little more robust. In case someone copy-and-pastes the code.

The TextButton example was recently updated: https://github.com/flutter/flutter/pull/144583

examples/api/lib/material/text_button/text_button.0.dart

@@ -55,7 +55,7 @@ class _TextButtonExampleState extends State<TextButtonExample> {
   TextDirection textDirection = TextDirection.ltr;
   ThemeMode themeMode = ThemeMode.light;
   late final ScrollController scrollController;
-  bool isRunning = false;
+  Future<void>? currentAction;
 
   static const Widget verticalSpacer = SizedBox(height: 16);
   static const Widget horizontalSpacer = SizedBox(width: 32);
@@ -345,17 +345,22 @@ class _TextButtonExampleState extends State<TextButtonExample> {
       // to provide one.
       TextButton(
         onPressed: () async {
-          setState(() { isRunning = true; });
-          Future<void>.delayed(const Duration(seconds: 1), () {
-            // Simulate a time consuming action.
-            setState(() { isRunning = false; });
+          // This is slightly complicated so that if the user presses the button
+          // while the current Future.delayed action is running, the currentAction
+          // flag is only reset to null after the _new_ action completes.
+          late final Future<void> thisAction;
+          thisAction = Future<void>.delayed(const Duration(seconds: 1), () {
+            if (currentAction == thisAction) {
+              setState(() { currentAction = null; });
+            }
           });
+          setState(() { currentAction = thisAction; });
         },
         style: TextButton.styleFrom(
           overlayColor: Colors.transparent,
           foregroundBuilder: (BuildContext context, Set<MaterialState> states, Widget? child) {
             late final ImageProvider image;
-            if (isRunning) {
+            if (currentAction != null) {
               image = runningImage;
             } else if (states.contains(MaterialState.pressed)) {
               image = pressedImage;
@@ -401,8 +406,6 @@ class _TextButtonExampleState extends State<TextButtonExample> {
         ),
         horizontalSpacer,
 
-        // All of the button examples appear below. They're arranged in two columns.
-
         Expanded(
           child:  Scrollbar(
             controller: scrollController,

examples/api/test/material/text_button/text_button.0_test.dart

@@ -55,8 +55,8 @@ void main() {
     await tester.pumpAndSettle();
 
     final Finder smileyButton = find.byType(TextButton).last;
-    await tester.tap(smileyButton); // Smiley image button
-    await tester.pumpAndSettle();
+    await tester.tap(smileyButton);
+    await tester.pump();
 
     String smileyButtonImageUrl() {
       final AnimatedContainer container = tester.widget<AnimatedContainer>(
@@ -66,6 +66,7 @@ void main() {
       final NetworkImage image = decoration.image!.image as NetworkImage;
       return image.url;
     }
+
     // The smiley button's onPressed method changes the button image
     // for one second to simulate a long action running. The button's
     // image changes while the action is running.
@@ -73,6 +74,18 @@ void main() {
     await tester.pump(const Duration(seconds: 1));
     expect(smileyButtonImageUrl().endsWith('text_button_nhu_default.png'), isTrue);
 
+    // Pressing the smiley button while the one second action is
+    // underway starts a new one section action. The button's image
+    // doesn't change until the second action has finished.
+    await tester.tap(smileyButton);
+    await tester.pump(const Duration(milliseconds: 500));
+    expect(smileyButtonImageUrl().endsWith('text_button_nhu_end.png'), isTrue);
+    await tester.tap(smileyButton); // Second button press.
+    await tester.pump(const Duration(milliseconds: 500));
+    expect(smileyButtonImageUrl().endsWith('text_button_nhu_end.png'), isTrue);
+    await tester.pump(const Duration(milliseconds: 500));
+    expect(smileyButtonImageUrl().endsWith('text_button_nhu_default.png'), isTrue);
+
     await tester.tap(find.byType(Switch).at(0)); // Dark Mode Switch
     await tester.pumpAndSettle();