fix(legacy): show taskbar progress and badge on this app's window

lib/src/legacy/window_manager.dart

@@ -4,7 +4,8 @@ import 'dart:async';
 import 'dart:io';
 import 'dart:ui' show Brightness, Color, Offset, PlatformDispatcher, Rect, Size;
 
-import 'package:flutter/foundation.dart' show ObserverList, VoidCallback;
+import 'package:flutter/foundation.dart'
+    show ObserverList, VoidCallback, visibleForTesting;
 import 'package:flutter/painting.dart' show Alignment;
 import 'package:nativeapi/nativeapi.dart' as nativeapi;
 import 'package:nativeapi_flutter/nativeapi_flutter.dart'
@@ -66,6 +67,15 @@ class WindowManager {
   nativeapi.Window? _window;
   nativeapi.ListenerId? _nativeListenerId;
 
+  /// Addresses [window] instead of the platform's current window, or goes
+  /// back to the current window with null. For tests of this bridge only.
+  @visibleForTesting
+  void debugBindWindow(nativeapi.Window? window) {
+    _unwireNativeEvents();
+    _window = window;
+    if (_listeners.isNotEmpty || _isPreventClose) _wireNativeEvents();
+  }
+
   bool _isPreventClose = false;
   bool _isDestroying = false;
   bool _isMaximized = false;
@@ -569,11 +579,33 @@ class WindowManager {
     _target?.isVisibleInTaskbar = !isSkipTaskbar;
   }
 
+  /// Replaces [nativeapi.Application.instance]. For tests of this bridge only.
+  @visibleForTesting
+  nativeapi.Application? debugApplicationOverride;
+
+  nativeapi.Application get _application =>
+      debugApplicationOverride ?? nativeapi.Application.instance;
+
   /// Sets progress value in progress bar. Valid range is [0, 1.0].
   ///
   /// @platforms macos,windows
   Future<void> setProgressBar(double progress) async {
-    tryNative(() => nativeapi.Application.instance.setProgressBar(progress));
+    final window = _target;
+    tryNative(() {
+      _designatePrimaryWindow(window);
+      _application.setProgressBar(progress);
+    });
+  }
+
+  // The taskbar progress and badge belong to the application's primary
+  // window. Without one, Windows falls back to the first visible titled
+  // top-level window on the desktop, which need not be this app's. Designate
+  // the addressed window unless the app chose a primary window itself.
+  void _designatePrimaryWindow(nativeapi.Window? window) {
+    if (window == null) return;
+    final application = _application;
+    if (application.getPrimaryWindow() != null) return;
+    application.setPrimaryWindow(window);
   }
 
   /// Sets window/taskbar icon.
@@ -620,7 +652,11 @@ class WindowManager {
   ///
   /// @platforms macos
   Future<void> setBadgeLabel([String? label]) async {
-    tryNative(() => nativeapi.Application.instance.setBadgeLabel(label ?? ''));
+    final window = _target;
+    tryNative(() {
+      _designatePrimaryWindow(window);
+      _application.setBadgeLabel(label ?? '');
+    });
   }
 
   /// Returns `bool` - Whether the window has a shadow. On Windows, always

test/legacy_taskbar_test.dart

@@ -0,0 +1,81 @@
+// The taskbar progress and badge of package:window_manager/legacy.dart.
+// ignore_for_file: deprecated_member_use_from_same_package
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:nativeapi/nativeapi.dart' as nativeapi;
+import 'package:window_manager/legacy.dart';
+
+// A nativeapi window simulated in Dart; no native window is created.
+class _FakeNativeWindow extends nativeapi.Window {
+  _FakeNativeWindow() : super.borrowed(0);
+}
+
+// Only the primary window and taskbar calls the bridge makes; any other
+// member throws.
+class _FakeApplication implements nativeapi.Application {
+  nativeapi.Window? primaryWindow;
+  final List<String> calls = <String>[];
+
+  @override
+  nativeapi.Window? getPrimaryWindow() => primaryWindow;
+
+  @override
+  void setPrimaryWindow(nativeapi.Window? window) {
+    calls.add('setPrimaryWindow');
+    primaryWindow = window;
+  }
+
+  @override
+  bool setProgressBar(double progress) {
+    calls.add('setProgressBar($progress)');
+    return true;
+  }
+
+  @override
+  bool setBadgeLabel(String label) {
+    calls.add('setBadgeLabel($label)');
+    return true;
+  }
+
+  @override
+  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
+}
+
+void main() {
+  late _FakeApplication application;
+
+  setUp(() {
+    application = _FakeApplication();
+    windowManager.debugApplicationOverride = application;
+  });
+
+  tearDown(() {
+    windowManager.debugApplicationOverride = null;
+    windowManager.debugBindWindow(null);
+  });
+
+  test('progress and badge designate the window as primary', () async {
+    final window = _FakeNativeWindow();
+    windowManager.debugBindWindow(window);
+
+    await windowManager.setProgressBar(0.5);
+    expect(application.primaryWindow, same(window));
+    await windowManager.setBadgeLabel('3');
+    expect(application.calls, [
+      'setPrimaryWindow',
+      'setProgressBar(0.5)',
+      'setBadgeLabel(3)',
+    ]);
+  });
+
+  test('a primary window the app chose is kept', () async {
+    final chosen = _FakeNativeWindow();
+    application.primaryWindow = chosen;
+    windowManager.debugBindWindow(_FakeNativeWindow());
+
+    await windowManager.setProgressBar(1);
+    await windowManager.setBadgeLabel();
+    expect(application.primaryWindow, same(chosen));
+    expect(application.calls, ['setProgressBar(1.0)', 'setBadgeLabel()']);
+  });
+}