Fixed hex color picker in material 3 demo (#2578)

This pull request fixes the problem where the color picker wasn't
handling hex values correctly.

Fixes #2577

material_3_demo/lib/color_box.dart

@@ -66,14 +66,13 @@ class _ColorBoxState extends State<ColorBox> {
                     onPressed: () async {
                       final messenger = ScaffoldMessenger.of(context);
                       // Copy color as hex to clipboard
-                      String hex = '#';
                       final c = widget.color;
-                      // Will change from int 0-255 to double 0.0-1.0 in 3.26+
-                      // The properties also change from red/green/blue to r/g/b
-                      // hex += (c.[r g b] * 255.0).round().toRadixString(16).padLeft(2, '0');
-                      hex += c.r.round().toRadixString(16).padLeft(2, '0');
-                      hex += c.g.round().toRadixString(16).padLeft(2, '0');
-                      hex += c.b.round().toRadixString(16).padLeft(2, '0');
+
+                      final hex =
+                          '#${_colorChannelToHex(c.r)}'
+                          '${_colorChannelToHex(c.g)}'
+                          '${_colorChannelToHex(c.b)}';
+
                       final data = ClipboardData(text: hex);
                       await Clipboard.setData(data);
                       messenger.hideCurrentSnackBar();
@@ -90,3 +89,8 @@ class _ColorBoxState extends State<ColorBox> {
     );
   }
 }
+
+String _colorChannelToHex(double value) {
+  final intVal = (value * 255).round();
+  return intVal.toRadixString(16).padLeft(2, '0');
+}

material_3_demo/test/color_screen_test.dart

@@ -2,8 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui';
+
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:material_3_demo/color_box.dart';
 import 'package:material_3_demo/color_palettes_screen.dart';
 import 'package:material_3_demo/main.dart';
 import 'package:material_3_demo/scheme.dart';
@@ -88,4 +92,66 @@ void main() {
     expect(find.text('Dark ColorScheme'), findsOneWidget);
     expect(find.byType(SchemePreview, skipOffstage: false), findsNWidgets(2));
   });
+
+  testWidgets(
+    'ColorBox displays correct info and copies hex color on button tap',
+    (tester) async {
+      TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+          .setMockMessageHandler('flutter/platform', (_) async {
+            // To intercept method calls to 'Clipboard.setData'
+            return const JSONMethodCodec().encodeSuccessEnvelope(null);
+          });
+      const hexColor = 0xFF3d3d8d;
+      const testColor = Color(hexColor);
+      const onTestColor = Colors.white;
+      const testLabel = 'Test Label';
+      const testTone = '50';
+
+      final gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
+
+      // Wrap in MaterialApp + Scaffold so we can show SnackBars
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: ColorBox(
+              label: testLabel,
+              tone: testTone,
+              color: testColor,
+              onColor: onTestColor,
+              height: 100,
+              width: 100,
+              displayPaletteInfo: true,
+            ),
+          ),
+        ),
+      );
+
+      expect(find.text(testLabel), findsOneWidget);
+      expect(find.text(testTone), findsOneWidget);
+
+      // The copy icon should NOT be there initially (only appears on hover).
+      expect(find.byIcon(Icons.copy), findsNothing);
+
+      await gesture.addPointer(location: Offset.zero);
+      addTearDown(gesture.removePointer);
+      await tester.pump();
+      await gesture.moveTo(tester.getCenter(find.byType(ColorBox)));
+      await tester.pumpAndSettle();
+
+      expect(find.byIcon(Icons.copy), findsOneWidget);
+
+      // Tap the copy icon, which copies the hex to clipboard and shows a SnackBar.
+      await tester.tap(find.byIcon(Icons.copy));
+      await tester.pumpAndSettle();
+
+      expect(find.byType(SnackBar), findsOneWidget);
+
+      expect(
+        find.text(
+          'Copied #${hexColor.toRadixString(16).substring(2)} to clipboard',
+        ),
+        findsOneWidget,
+      );
+    },
+  );
 }