maui-app-lifecycle（毛伊岛应用程序生命周期）

.NET MAUI App Lifecycle

Critical Behavioral Gotchas

⚠️ Resumed ≠ first launch

Resumed only fires when returning from the Stopped state. On first launch the sequence is Created → Activated — Resumed is never called.

// ❌ Putting initialization logic in OnResumed — won't run on first launch
protected override void OnResumed()
{
    LoadUserProfile();  // Skipped on cold start!
}

// ✅ Use OnActivated for logic that must run on every foreground entry
protected override void OnActivated()
{
    LoadUserProfile();  // Runs on both first launch and resume
}

⚠️ Deactivated ≠ Stopped

A dialog, split-screen, or notification pull-down triggers Deactivated without Stopped. Don't save heavy state on Deactivated — the app may never actually background.

// ❌ Heavy save on every deactivation — fires too often
protected override void OnDeactivated()
{
    await SaveAllDataToDatabase();  // Wasteful for a dialog appearance
}

// ✅ Save state only when truly backgrounded
protected override void OnStopped()
{
    await SaveAllDataToDatabase();
}

⚠️ Android back button skips Stopped

On Android, pressing the hardware back button may call Destroying without Stopped if the activity finishes. Critical save logic in OnStopped alone can be missed.

// ✅ Save in both Stopped and Destroying for safety on Android
protected override void OnStopped()
{
    base.OnStopped();
    SaveDraft();
}

protected override void OnDestroying()
{
    base.OnDestroying();
    SaveDraft();  // Catches Android back-button finish
}

⚠️ Multiple windows fire independently

On iPad, Mac Catalyst, and desktop Windows, each Window instance fires its own lifecycle events independently. Don't assume a single global lifecycle.

Performance: Keep Handlers Fast

Long-running work in lifecycle handlers causes ANR kills on Android (5s timeout) and watchdog kills on iOS (limited background time).

// ❌ Blocking the lifecycle handler
protected override void OnStopped()
{
    Thread.Sleep(3000);  // ANR on Android!
    SaveData();
}

// ✅ Fire-and-forget or use a brief async save
protected override void OnStopped()
{
    base.OnStopped();
    Preferences.Set("draft_text", _viewModel.DraftText);  // Fast, synchronous
}

For larger state, use SecureStorage or file-based serialization — but keep it under 1–2 seconds.

iOS Scene Lifecycle

iOS 13+ uses the scene lifecycle (SceneWillConnect, etc.). Older delegate methods are still forwarded by MAUI, but you should target scene-based APIs for modern iOS.

State Preservation Checklist

• Transient UI state (scroll position, draft text) saved in OnStopped
• State restored in OnResumed — not in OnActivated (avoid double-restore)
• No heavy I/O in OnDeactivated — it fires too frequently
• Android: critical save logic also in OnDestroying (back-button case)
• Lifecycle handlers complete in under 2 seconds
• Multi-window apps handle per-window state independently