.NET 8应用前台点击推送通知崩溃：Window was already created

问题描述 #

我在MAUI应用中配置了推送通知，当应用处于打开状态时点击通知，应用崩溃并抛出如下异常：

[mono-rt] [ERROR] FATAL UNHANDLED EXCEPTION: System.InvalidOperationException: Window was already created
[mono-rt]    at Microsoft.Maui.Controls.Window.Microsoft.Maui.IWindow.Created() in D:\a\_work\1\s\src\Controls\src\Core\Window\Window.cs:line 491
[mono-rt]    at Microsoft.Maui.LifecycleEvents.AppHostBuilderExtensions.<>c.<OnConfigureLifeCycle>b__2_0(Activity activity, Bundle bundle) in D:\a\_work\1\s\src\Core\src\Hosting\LifecycleEvents\AppHostBuilderExtensions.Android.cs:line 23
[mono-rt]    at Microsoft.Maui.MauiAppCompatActivity.<>c__DisplayClass8_0.<OnPostCreate>b__0(OnPostCreate del) in D:\a\_work\1\s\src\Core\src\Platform\Android\MauiAppCompatActivity.Lifecycle.cs:line 61
[mono-rt]    at Microsoft.Maui.LifecycleEvents.LifecycleEventServiceExtensions.InvokeLifecycleEvents[OnPostCreate](IServiceProvider services, Action`1 action) in D:\a\_work\1\s\src\Core\src\LifecycleEvents\LifecycleEventServiceExtensions.cs:line 31
[mono-rt]    at Microsoft.Maui.MauiAppCompatActivity.OnPostCreate(Bundle savedInstanceState) in D:\a\_work\1\s\src\Core\src\Platform\Android\MauiAppCompatActivity.Lifecycle.cs:line 61
[mono-rt]    at DailyBudgetMAUIApp.MainActivity.OnPostCreate(Bundle savedInstanceState) in C:\Users\darre\OneDrive\Documents\OneDrive\Documents\DailyBudgetMAUIApp\DailyBudgetMAUIApp\Platforms\Android\MainActivity.cs:line 20
[mono-rt]    at Android.App.Activity.n_OnPostCreate_Landroid_os_Bundle_(IntPtr jnienv, IntPtr native__this, IntPtr native_savedInstanceState) in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/obj/Release/net8.0/android-34/mcw/Android.App.Activity.cs:line 4488
[mono-rt]    at Android.Runtime.JNINativeWrapper.Wrap_JniMarshal_PPL_V(_JniMarshal_PPL_V callback, IntPtr jnienv, IntPtr klazz, IntPtr p0) in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Android.Runtime/JNINativeWrapper.g.cs:line 125

崩溃发生在OnPostCreate方法中，原因是窗口已存在，但无法推进解决，尝试搜索和调试均无果。

解决方案 #

1. 配置Activity的LaunchMode #

修改Platforms/Android/MainActivity.cs的Activity特性，将LaunchMode设置为SingleTop，避免前台时重复创建Activity实例：

[Activity(Theme = "@style/Maui.SplashTheme", 
          MainLauncher = true, 
          LaunchMode = LaunchMode.SingleTop, 
          ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation | ConfigChanges.UiMode | ConfigChanges.ScreenLayout | ConfigChanges.SmallestScreenSize | ConfigChanges.Density)]
public class MainActivity : MauiAppCompatActivity
{
    // 现有代码
}

SingleTop模式下，若Activity已在栈顶，系统会调用OnNewIntent而非创建新实例，从根源避免重复创建窗口。

2. 重写OnNewIntent处理通知数据 #

在MainActivity中重写OnNewIntent方法，直接处理推送通知的跳转逻辑，绕过可能触发窗口重建的流程：

protected override void OnNewIntent(Intent intent)
{
    base.OnNewIntent(intent);
    
    if (intent.Extras != null)
    {
        // 提取通知数据
        var payload = intent.Extras.GetString("notification_payload");
        // 通过Messenger通知MAUI主线程处理导航
        WeakReferenceMessenger.Default.Send(new NotificationNavMessage(payload));
    }
}

同时，确保推送通知的PendingIntent使用FlagUpdateCurrent标记，避免生成重复的Intent：

var pendingIntent = PendingIntent.GetActivity(context, 0, intent, PendingIntentFlags.UpdateCurrent | PendingIntentFlags.Immutable);

3. 清理OnPostCreate中的自定义代码 #

检查MainActivity.cs的OnPostCreate方法，移除手动触发窗口创建的代码。MAUI框架已自动处理窗口生命周期，无需手动调用：

protected override void OnPostCreate(Bundle savedInstanceState)
{
    base.OnPostCreate(savedInstanceState);
    // 移除类似 ((IWindow)Window).Created() 的代码
}

4. 更新MAUI版本 #

该异常可能是MAUI框架的已知生命周期bug，尝试升级到最新稳定版.NET MAUI，官方通常会修复此类窗口管理问题。

内容的提问来源于stack exchange，提问作者Darren Fillis