Force writing preferences to file when application stops

app/app.go

@@ -148,6 +148,11 @@ func newAppWithDriver(d fyne.Driver, id string) fyne.App {
 	fyne.SetCurrentApp(newApp)
 
 	newApp.prefs = newApp.newDefaultPreferences()
+	newApp.lifecycle.(*app.Lifecycle).SetAfterStopped(func() {
+		if prefs, ok := newApp.prefs.(*preferences); ok {
+			prefs.forceImmediateSave()
+		}
+	})
 	newApp.settings = loadSettings()
 	store := &store{a: newApp}
 	store.Docs = makeStoreDocs(id, newApp.prefs, store)

app/preferences.go

@@ -19,12 +19,25 @@ type preferences struct {
 	savedRecently       bool
 	changedDuringSaving bool
 
-	app *fyneApp
+	app                 *fyneApp
+	needsSaveBeforeExit bool
 }
 
 // Declare conformity with Preferences interface
 var _ fyne.Preferences = (*preferences)(nil)
 
+// forceImmediateSave writes preferences to file immediately, ignoring the debouncing
+// logic in the change listener. Does nothing if preferences are not backed with a file.
+func (p *preferences) forceImmediateSave() {
+	if !p.needsSaveBeforeExit {
+		return
+	}
+	err := p.save()
+	if err != nil {
+		fyne.LogError("Failed on force saving preferences", err)
+	}
+}
+
 func (p *preferences) resetSavedRecently() {
 	go func() {
 		time.Sleep(time.Millisecond * 100) // writes are not always atomic. 10ms worked, 100 is safer.
@@ -49,6 +62,7 @@ func (p *preferences) saveToFile(path string) error {
 	p.savedRecently = true
 	p.prefLock.Unlock()
 	defer p.resetSavedRecently()
+
 	err := os.MkdirAll(filepath.Dir(path), 0700)
 	if err != nil { // this is not an exists error according to docs
 		return err
@@ -132,6 +146,7 @@ func newPreferences(app *fyneApp) *preferences {
 		return p
 	}
 
+	p.needsSaveBeforeExit = true
 	p.AddChangeListener(func() {
 		if p != app.prefs {
 			return

internal/app/lifecycle.go

@@ -16,6 +16,14 @@ type Lifecycle struct {
 	onBackground atomic.Value // func()
 	onStarted    atomic.Value // func()
 	onStopped    atomic.Value // func()
+
+	internalAfterStoppedTrigger atomic.Value // func()
+}
+
+// SetAfterStopped is an internal function that lets Fyne schedule a clean-up after
+// the user-provided stopped hook.
+func (l *Lifecycle) SetAfterStopped(f func()) {
+	l.internalAfterStoppedTrigger.Store(f)
 }
 
 // SetOnEnteredForeground hooks into the the app becoming foreground.
@@ -64,10 +72,15 @@ func (l *Lifecycle) TriggerStarted() {
 	}
 }
 
-// TriggerStopped will call the stopped hook, if one is registered.
+// TriggerStopped will call the stopped hook, if one is registered,
+// and an internal stopped hook after that.
 func (l *Lifecycle) TriggerStopped() {
 	f := l.onStopped.Load()
 	if ff, ok := f.(func()); ok && ff != nil {
 		ff()
 	}
+	f = l.internalAfterStoppedTrigger.Load()
+	if ff, ok := f.(func()); ok && ff != nil {
+		ff()
+	}
 }