Add new callback-based settings listener API

app/app_windows.go

@@ -90,5 +90,7 @@ func runScript(name, script string) {
 }
 
 func watchTheme(s *settings) {
-	go internalapp.WatchTheme(s.setupTheme)
+	go internalapp.WatchTheme(func() {
+		fyne.Do(s.setupTheme)
+	})
 }

app/app_xdg.go

@@ -118,13 +118,13 @@ func watchTheme(s *settings) {
 		// Theme lookup hangs on some desktops. Update theme variant cache from within goroutine.
 		themeVariant := findFreedesktopColorScheme()
 		internalapp.CurrentVariant.Store(uint64(themeVariant))
-		s.applyVariant(themeVariant)
+		fyne.Do(func() { s.applyVariant(themeVariant) })
 
 		portalSettings.OnSignalSettingChanged(func(changed portalSettings.Changed) {
 			if changed.Namespace == appearance.Namespace && changed.Key == "color-scheme" {
 				themeVariant := colorSchemeToThemeVariant(appearance.ColorScheme(changed.Value.(uint32)))
 				internalapp.CurrentVariant.Store(uint64(themeVariant))
-				s.applyVariant(themeVariant)
+				fyne.Do(func() { s.applyVariant(themeVariant) })
 			}
 		})
 	}()

app/cloud_test.go

@@ -45,7 +45,9 @@ func TestFyneApp_transitionCloud(t *testing.T) {
 	a.Preferences().AddChangeListener(func() {
 		preferenceChanged = true
 	})
-	a.Settings().AddChangeListener(settingsChan)
+	a.Settings().AddListener(func(s fyne.Settings) {
+		go func() { settingsChan <- s }()
+	})
 
 	done := make(chan struct{})
 	go func() {

app/settings.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"os"
 	"path/filepath"
-	"sync"
 
 	"fyne.io/fyne/v2"
 	"fyne.io/fyne/v2/internal/app"
@@ -33,11 +32,11 @@ func (sc *SettingsSchema) StoragePath() string {
 var _ fyne.Settings = (*settings)(nil)
 
 type settings struct {
-	propertyLock   sync.RWMutex
 	theme          fyne.Theme
 	themeSpecified bool
 	variant        fyne.ThemeVariant
 
+	listeners       []func(fyne.Settings)
 	changeListeners async.Map[chan fyne.Settings, bool]
 	watcher         any // normally *fsnotify.Watcher or nil - avoid import in this file
 
@@ -49,8 +48,6 @@ func (s *settings) BuildType() fyne.BuildType {
 }
 
 func (s *settings) PrimaryColor() string {
-	s.propertyLock.RLock()
-	defer s.propertyLock.RUnlock()
 	return s.schema.PrimaryColor
 }
 
@@ -59,8 +56,6 @@ func (s *settings) PrimaryColor() string {
 //
 // Deprecated: Use container.NewThemeOverride to change the appearance of part of your application.
 func (s *settings) OverrideTheme(theme fyne.Theme, name string) {
-	s.propertyLock.Lock()
-	defer s.propertyLock.Unlock()
 	s.schema.PrimaryColor = name
 	s.theme = theme
 }
@@ -70,8 +65,6 @@ func (s *settings) Theme() fyne.Theme {
 		fyne.LogError("Attempt to access current Fyne theme when no app is started", nil)
 		return nil
 	}
-	s.propertyLock.RLock()
-	defer s.propertyLock.RUnlock()
 	return s.theme
 }
 
@@ -89,23 +82,17 @@ func (s *settings) ThemeVariant() fyne.ThemeVariant {
 }
 
 func (s *settings) applyTheme(theme fyne.Theme, variant fyne.ThemeVariant) {
-	s.propertyLock.Lock()
-	defer s.propertyLock.Unlock()
 	s.variant = variant
 	s.theme = theme
 	s.apply()
 }
 
 func (s *settings) applyVariant(variant fyne.ThemeVariant) {
-	s.propertyLock.Lock()
-	defer s.propertyLock.Unlock()
 	s.variant = variant
 	s.apply()
 }
 
 func (s *settings) Scale() float32 {
-	s.propertyLock.RLock()
-	defer s.propertyLock.RUnlock()
 	if s.schema.Scale < 0.0 {
 		return 1.0 // catching any really old data still using the `-1`  value for "auto" scale
 	}
@@ -116,6 +103,11 @@ func (s *settings) AddChangeListener(listener chan fyne.Settings) {
 	s.changeListeners.Store(listener, true) // the boolean is just a dummy value here.
 }
 
+func (s *settings) AddListener(listener func(fyne.Settings)) {
+	s.listeners = append(s.listeners, listener)
+}
+
+// must be called from main goroutine
 func (s *settings) apply() {
 	s.changeListeners.Range(func(listener chan fyne.Settings, _ bool) bool {
 		select {
@@ -126,6 +118,10 @@ func (s *settings) apply() {
 		}
 		return true
 	})
+
+	for _, l := range s.listeners {
+		l(s)
+	}
 }
 
 func (s *settings) fileChanged() {

cmd/fyne_demo/tutorials/welcome.go

@@ -59,21 +59,15 @@ func welcomeScreen(_ fyne.Window) fyne.CanvasObject {
 	slideBG := container.New(underlayer, underlay)
 	footerBG := canvas.NewRectangle(shadowColor)
 
-	listen := make(chan fyne.Settings)
-	fyne.CurrentApp().Settings().AddChangeListener(listen)
-	go func() {
-		for range listen {
-			fyne.Do(func() {
-				bgColor = withAlpha(theme.Color(theme.ColorNameBackground), 0xe0)
-				bg.FillColor = bgColor
-				bg.Refresh()
-
-				shadowColor = withAlpha(theme.Color(theme.ColorNameBackground), 0x33)
-				footerBG.FillColor = bgColor
-				footer.Refresh()
-			})
-		}
-	}()
+	fyne.CurrentApp().Settings().AddListener(func(fyne.Settings) {
+		bgColor = withAlpha(theme.Color(theme.ColorNameBackground), 0xe0)
+		bg.FillColor = bgColor
+		bg.Refresh()
+
+		shadowColor = withAlpha(theme.Color(theme.ColorNameBackground), 0x33)
+		footerBG.FillColor = bgColor
+		footer.Refresh()
+	})
 
 	underlay.Resize(fyne.NewSize(1024, 1024))
 	scroll.OnScrolled = func(p fyne.Position) {

internal/driver/glfw/canvas_test.go

@@ -541,7 +541,9 @@ func TestGlCanvas_Scale(t *testing.T) {
 }
 
 func TestGlCanvas_SetContent(t *testing.T) {
-	fyne.CurrentApp().Settings().SetTheme(internalTest.DarkTheme(theme.DefaultTheme()))
+	runOnMain(func() {
+		fyne.CurrentApp().Settings().SetTheme(internalTest.DarkTheme(theme.DefaultTheme()))
+	})
 	var menuHeight float32
 	if build.HasNativeMenu {
 		menuHeight = 0

internal/driver/glfw/loop.go

@@ -99,13 +99,24 @@ func (d *gLDriver) runGL() {
 	if d.trayStart != nil {
 		d.trayStart()
 	}
+
+	fyne.CurrentApp().Settings().AddListener(func(set fyne.Settings) {
+		painter.ClearFontCache()
+		cache.ResetThemeCaches()
+		app.ApplySettingsWithCallback(set, fyne.CurrentApp(), func(w fyne.Window) {
+			c, ok := w.Canvas().(*glCanvas)
+			if !ok {
+				return
+			}
+			c.applyThemeOutOfTreeObjects()
+			c.reloadScale()
+		})
+	})
+
 	if f := fyne.CurrentApp().Lifecycle().(*app.Lifecycle).OnStarted(); f != nil {
 		f()
 	}
 
-	settingsChange := make(chan fyne.Settings)
-	fyne.CurrentApp().Settings().AddChangeListener(settingsChange)
-
 	eventTick := time.NewTicker(time.Second / 60)
 	for {
 		select {
@@ -149,23 +160,10 @@ func (d *gLDriver) runGL() {
 						view.SetSize(w.shouldWidth, w.shouldHeight)
 					}
 				}
-
 			}
 
 			d.animation.TickAnimations()
 			d.drawSingleFrame()
-		case set := <-settingsChange:
-			painter.ClearFontCache()
-			cache.ResetThemeCaches()
-			app.ApplySettingsWithCallback(set, fyne.CurrentApp(), func(w fyne.Window) {
-				c, ok := w.Canvas().(*glCanvas)
-				if !ok {
-					return
-				}
-				c.applyThemeOutOfTreeObjects()
-				c.reloadScale()
-			})
-
 		}
 	}
 }

internal/driver/mobile/driver.go

@@ -168,9 +168,20 @@ func (d *driver) Run() {
 
 	app.Main(func(a app.App) {
 		d.app = a
-		settingsChange := make(chan fyne.Settings)
 		d.queuedFuncs = async.NewUnboundedChan[func()]()
-		fyne.CurrentApp().Settings().AddChangeListener(settingsChange)
+
+		fyne.CurrentApp().Settings().AddListener(func(s fyne.Settings) {
+			painter.ClearFontCache()
+			cache.ResetThemeCaches()
+			intapp.ApplySettingsWithCallback(s, fyne.CurrentApp(), func(w fyne.Window) {
+				c, ok := w.Canvas().(*canvas)
+				if !ok {
+					return
+				}
+				c.applyThemeOutOfTreeObjects()
+			})
+		})
+
 		draw := time.NewTicker(time.Second / 60)
 		defer func() {
 			l := fyne.CurrentApp().Lifecycle().(*intapp.Lifecycle)
@@ -191,16 +202,6 @@ func (d *driver) Run() {
 			select {
 			case <-draw.C:
 				d.sendPaintEvent()
-			case set := <-settingsChange:
-				painter.ClearFontCache()
-				cache.ResetThemeCaches()
-				intapp.ApplySettingsWithCallback(set, fyne.CurrentApp(), func(w fyne.Window) {
-					c, ok := w.Canvas().(*canvas)
-					if !ok {
-						return
-					}
-					c.applyThemeOutOfTreeObjects()
-				})
 			case fn := <-d.queuedFuncs.Out():
 				fn()
 			case e, ok := <-a.Events():

settings.go

@@ -27,7 +27,17 @@ type Settings interface {
 	// Since: 1.4
 	PrimaryColor() string
 
+	// AddChangeListener subscribes to settings change events over a channel.
+	//
+	// Deprecated: Use AddListener instead, which uses a callback-based API
+	// with the callback guaranteed to be invoked on the app goroutine.
 	AddChangeListener(chan Settings)
+
+	// AddListener registers a callback that is invoked whenever the settings change.
+	//
+	// Since: 2.6
+	AddListener(func(Settings))
+
 	BuildType() BuildType
 
 	ShowAnimations() bool

test/app.go

@@ -182,6 +182,8 @@ type testSettings struct {
 	scale        float32
 	theme        fyne.Theme
 
+	listenersLock   sync.Mutex
+	listeners       []func(fyne.Settings)
 	changeListeners []chan fyne.Settings
 	propertyLock    sync.RWMutex
 	app             *app
@@ -193,6 +195,12 @@ func (s *testSettings) AddChangeListener(listener chan fyne.Settings) {
 	s.changeListeners = append(s.changeListeners, listener)
 }
 
+func (s *testSettings) AddListener(listener func(fyne.Settings)) {
+	s.propertyLock.Lock()
+	defer s.propertyLock.Unlock()
+	s.listeners = append(s.listeners, listener)
+}
+
 func (s *testSettings) BuildType() fyne.BuildType {
 	return fyne.BuildStandard
 }
@@ -253,6 +261,12 @@ func (s *testSettings) apply() {
 		cache.ResetThemeCaches()
 		intapp.ApplySettings(s, s.app)
 		s.app.propertyLock.Unlock()
+
+		s.listenersLock.Lock()
+		defer s.listenersLock.Unlock()
+		for _, l := range s.listeners {
+			l(s)
+		}
 	}, false)
 
 	s.app.propertyLock.Lock()

test/app_test.go

@@ -23,7 +23,9 @@ func TestFyneApp_transitionCloud(t *testing.T) {
 	a.Preferences().AddChangeListener(func() {
 		preferenceChanged = true
 	})
-	a.Settings().AddChangeListener(settingsChan)
+	a.Settings().AddListener(func(s fyne.Settings) {
+		go func() { settingsChan <- s }()
+	})
 	a.SetCloudProvider(p)
 
 	<-settingsChan // settings were updated

theme/themedtestapp_test.go

@@ -107,6 +107,9 @@ func (t *themedApp) ShowAnimations() bool {
 func (t *themedApp) AddChangeListener(chan fyne.Settings) {
 }
 
+func (t *themedApp) AddListener(func(fyne.Settings)) {
+}
+
 func (t *themedApp) Clipboard() fyne.Clipboard {
 	return nil
 }