maui-app-lifecycle（毛伊岛应用程序生命周期）

.NET MAUI App Lifecycle

Handle application state transitions correctly in.NET MAUI. This skill covers the cross-platform Window lifecycle events, their platform-native mappings, and patterns for preserving state across backgrounding and resume cycles.

When to Use

• Saving or restoring state when the app backgrounds or resumes
• Subscribing to Window lifecycle events (Created, Activated, Deactivated, Stopped, Resumed, Destroying)
• Hooking into platform-native lifecycle callbacks via ConfigureLifecycleEvents
• Deciding where to place initialization, teardown, or refresh logic
• Understanding the difference between Deactivated and Stopped

When Not to Use

• Page-level navigation events — use Shell navigation guidance instead
• Registering services at startup — use dependency injection guidance instead
• Calling platform-specific APIs outside lifecycle context — use platform invoke guidance instead

Inputs

• The target lifecycle transition (e.g., "save draft when backgrounded", "refresh data on resume")
• Which platforms the developer targets (Android, iOS, Mac Catalyst, Windows)
• Whether the app uses multiple windows (iPad, Mac Catalyst, desktop Windows)

App States

A.NET MAUI app moves through four states:

Typical flow: Not Running → Running → Deactivated → Stopped → Running (resumed) or Not Running (terminated).

Window Lifecycle Events

Microsoft.Maui.Controls.Window exposes six cross-platform events:

Subscribing via CreateWindow

Override CreateWindow in your App class and attach event handlers:

public partial class App : Application
{
    protected override Window CreateWindow(IActivationState? activationState)
    {
        var window = base.CreateWindow(activationState);

        window.Created += (s, e) => Debug.WriteLine("Created");
        window.Activated += (s, e) => Debug.WriteLine("Activated");
        window.Deactivated += (s, e) => Debug.WriteLine("Deactivated");
        window.Stopped += (s, e) => Debug.WriteLine("Stopped");
        window.Resumed += (s, e) => Debug.WriteLine("Resumed");
        window.Destroying += (s, e) => Debug.WriteLine("Destroying");

        return window;
    }
}

Subscribing via a Custom Window Subclass

Create a Window subclass and override the virtual methods:

public class AppWindow : Window
{
    public AppWindow(Page page) : base(page) { }

    protected override void OnActivated() { /* refresh UI */ }
    protected override void OnStopped() { /* save state */ }
    protected override void OnResumed() { /* restore state */ }
    protected override void OnDestroying() { /* cleanup */ }
}

Return it from CreateWindow:

protected override Window CreateWindow(IActivationState? activationState)
    => new AppWindow(new AppShell());

Workflow: Save and Restore State on Background

1. Identify transient state — draft text, scroll position, form inputs, timer values.
2. Save in OnStopped — use Preferences for small values or file serialization for larger state.
3. Restore in OnResumed — read back saved values and apply to your view model.
4. Also save in OnDestroying on Android — the back button can skip Stopped entirely.
5. Keep handlers fast — complete within 1–2 seconds to avoid ANR on Android or watchdog kills on iOS.

protected override void OnStopped()
{
    base.OnStopped();
    Preferences.Set("draft_text", _viewModel.DraftText);
    Preferences.Set("scroll_y", _viewModel.ScrollY);
}

protected override void OnResumed()
{
    base.OnResumed();
    _viewModel.DraftText = Preferences.Get("draft_text", string.Empty);
    _viewModel.ScrollY = Preferences.Get("scroll_y", 0.0);
}

protected override void OnDestroying()
{
    base.OnDestroying();
    // Android back-button can skip Stopped
    Preferences.Set("draft_text", _viewModel.DraftText);
}

Platform Lifecycle Mapping

Android

iOS / Mac Catalyst

Windows (WinUI)

Hooking Native Lifecycle Directly

Use ConfigureLifecycleEvents in MauiProgram.cs when you need platform-specific callbacks beyond what Window events provide:

builder.ConfigureLifecycleEvents(events =>
{
#if ANDROID
    events.AddAndroid(android => android
        .OnCreate((activity, bundle) => Debug.WriteLine("Android OnCreate"))
        .OnResume(activity => Debug.WriteLine("Android OnResume"))
        .OnPause(activity => Debug.WriteLine("Android OnPause"))
        .OnStop(activity => Debug.WriteLine("Android OnStop"))
        .OnDestroy(activity => Debug.WriteLine("Android OnDestroy")));
#elif IOS || MACCATALYST
    events.AddiOS(ios => ios
        .DidBecomeActive(app => Debug.WriteLine("iOS DidBecomeActive"))
        .WillResignActive(app => Debug.WriteLine("iOS WillResignActive"))
        .DidEnterBackground(app => Debug.WriteLine("iOS DidEnterBackground"))
        .WillEnterForeground(app => Debug.WriteLine("iOS WillEnterForeground")));
#elif WINDOWS
    events.AddWindows(windows => windows
        .OnLaunched((app, args) => Debug.WriteLine("Windows OnLaunched"))
        .OnActivated((window, args) => Debug.WriteLine("Windows Activated"))
        .OnClosed((window, args) => Debug.WriteLine("Windows Closed")));
#endif
});

Common Pitfalls

1. Resumed does not fire on first launch. The initial sequence is Created → Activated. Use OnActivated for logic that must run on every foreground entry, not OnResumed.
2. Deactivated ≠ Stopped. A dialog, split-screen, or notification pull-down triggers Deactivated without Stopped. Do not perform heavy saves in OnDeactivated — the app may never actually background.
3. Android back button skips Stopped. On Android, pressing back may call Destroying directly without Stopped. Place critical save logic in both OnStopped and OnDestroying.
4. Multi-window apps fire events independently. On iPad, Mac Catalyst, and desktop Windows each Window instance fires its own lifecycle events. Do not assume a single global lifecycle.
5. Long-running handlers cause kills. Android enforces a ~5 second ANR timeout; iOS has limited background execution time. Keep lifecycle handlers synchronous and fast — use Preferences for quick saves, not database writes.
6. Do not use legacy Xamarin.Forms lifecycle methods. Application.OnStart(), Application.OnSleep(), and Application.OnResume() exist for backward compatibility but bypass Window-level events. In.NET MAUI, prefer Window lifecycle events (OnActivated, OnStopped, OnResumed, etc.) for correct multi-window behavior.