Allow a theme to override the form factor of the tabs to be mobile

container/apptabs.go

@@ -215,7 +215,7 @@ func (t *AppTabs) SetItems(items []*TabItem) {
 
 // SetTabLocation sets the location of the tab bar
 func (t *AppTabs) SetTabLocation(l TabLocation) {
-	t.location = tabsAdjustedLocation(l)
+	t.location = tabsAdjustedLocation(l, t)
 	t.Refresh()
 }
 
@@ -357,7 +357,7 @@ func (r *appTabsRenderer) buildTabButtons(count int) *fyne.Container {
 	buttons := &fyne.Container{}
 
 	var iconPos buttonIconPosition
-	if fyne.CurrentDevice().IsMobile() {
+	if isMobile(r.tabs) {
 		cells := count
 		if cells == 0 {
 			cells = 1
@@ -381,6 +381,7 @@ func (r *appTabsRenderer) buildTabButtons(count int) *fyne.Container {
 		if item.button == nil {
 			item.button = &tabButton{
 				onTapped: func() { r.appTabs.Select(item) },
+				tabs:     r.tabs,
 			}
 		}
 		button := item.button

container/apptabs_override_test.go

@@ -0,0 +1,35 @@
+//go:build !mobile
+
+package container_test
+
+import (
+	"testing"
+
+	"fyne.io/fyne/v2/container"
+	"fyne.io/fyne/v2/test"
+	"fyne.io/fyne/v2/widget"
+)
+
+func TestAppTabs_OverrideMobile(t *testing.T) {
+	test.NewTempApp(t)
+
+	item1 := &container.TabItem{Text: "Test1", Content: widget.NewLabel("Text 1")}
+	item2 := &container.TabItem{Text: "Test2", Content: widget.NewLabel("Text 2")}
+	item3 := &container.TabItem{Text: "Test3", Content: widget.NewLabel("Text 3")}
+	tabs := container.NewAppTabs(item1, item2, item3)
+	w := test.NewWindow(tabs)
+	defer w.Close()
+	w.SetPadded(false)
+	c := w.Canvas()
+
+	min := tabs.MinSize()
+	w.Resize(min)
+
+	test.AssertRendersToMarkup(t, "apptabs/desktop/tab_location_top.xml", c)
+
+	override := container.NewThemeOverride(tabs, test.Theme())
+	override.SetDeviceIsMobile(true)
+	w.Resize(min.AddWidthHeight(-4, -0))
+
+	test.AssertRendersToMarkup(t, "apptabs/mobile/tab_location_top.xml", c)
+}

container/doctabs.go

@@ -173,7 +173,7 @@ func (t *DocTabs) SetItems(items []*TabItem) {
 
 // SetTabLocation sets the location of the tab bar
 func (t *DocTabs) SetTabLocation(l TabLocation) {
-	t.location = tabsAdjustedLocation(l)
+	t.location = tabsAdjustedLocation(l, t)
 	t.Refresh()
 }
 
@@ -338,6 +338,7 @@ func (r *docTabsRenderer) buildTabButtons(count int, buttons *fyne.Container) {
 			item.button = &tabButton{
 				onTapped: func() { r.docTabs.Select(item) },
 				onClosed: func() { r.docTabs.close(item) },
+				tabs:     r.tabs,
 			}
 		}
 		button := item.button

container/tabs.go

@@ -8,6 +8,7 @@ import (
 	"fyne.io/fyne/v2/driver/desktop"
 	"fyne.io/fyne/v2/internal"
 	"fyne.io/fyne/v2/internal/build"
+	intTheme "fyne.io/fyne/v2/internal/theme"
 	"fyne.io/fyne/v2/theme"
 	"fyne.io/fyne/v2/widget"
 )
@@ -91,10 +92,20 @@ type baseTabs interface {
 	setTransitioning(bool)
 }
 
-func tabsAdjustedLocation(l TabLocation) TabLocation {
+func isMobile(b baseTabs) bool {
+	d := fyne.CurrentDevice()
+	mobile := intTheme.FeatureForWidget(intTheme.FeatureNameDeviceIsMobile, b)
+	if is, ok := mobile.(bool); ok {
+		return is
+	}
+
+	return d.IsMobile()
+}
+
+func tabsAdjustedLocation(l TabLocation, b baseTabs) TabLocation {
 	// Mobile has limited screen space, so don't put app tab bar on long edges
-	if d := fyne.CurrentDevice(); d.IsMobile() {
-		if o := d.Orientation(); fyne.IsVertical(o) {
+	if isMobile(b) {
+		if o := fyne.CurrentDevice().Orientation(); fyne.IsVertical(o) {
 			if l == TabLocationLeading {
 				return TabLocationTop
 			} else if l == TabLocationTrailing {
@@ -511,6 +522,8 @@ type tabButton struct {
 	onClosed      func()
 	text          string
 	textAlignment fyne.TextAlign
+
+	tabs baseTabs
 }
 
 func (b *tabButton) CreateRenderer() fyne.WidgetRenderer {
@@ -720,7 +733,7 @@ func (r *tabButtonRenderer) Refresh() {
 		r.icon.Hide()
 	}
 
-	if d := fyne.CurrentDevice(); r.button.onClosed != nil && (d.IsMobile() || r.button.hovered || r.close.hovered) {
+	if r.button.onClosed != nil && (isMobile(r.button.tabs) || r.button.hovered || r.close.hovered) {
 		r.close.Show()
 	} else {
 		r.close.Hide()

container/theme.go

@@ -3,6 +3,7 @@ package container
 import (
 	"fyne.io/fyne/v2"
 	"fyne.io/fyne/v2/internal/cache"
+	intTheme "fyne.io/fyne/v2/internal/theme"
 	"fyne.io/fyne/v2/widget"
 )
 
@@ -18,6 +19,8 @@ type ThemeOverride struct {
 	Theme   fyne.Theme
 
 	holder *fyne.Container
+
+	mobile bool
 }
 
 // NewThemeOverride provides a container where the child widgets are themed by the specified theme.
@@ -32,13 +35,13 @@ func NewThemeOverride(obj fyne.CanvasObject, th fyne.Theme) *ThemeOverride {
 	t := &ThemeOverride{Content: obj, Theme: th, holder: NewStack(obj)}
 	t.ExtendBaseWidget(t)
 
-	cache.OverrideTheme(obj, th)
+	cache.OverrideTheme(obj, addFeatures(th, t))
 	obj.Refresh() // required as the widgets passed in could have been initially rendered with default theme
 	return t
 }
 
 func (t *ThemeOverride) CreateRenderer() fyne.WidgetRenderer {
-	cache.OverrideTheme(t.Content, t.Theme)
+	cache.OverrideTheme(t.Content, addFeatures(t.Theme, t))
 
 	return widget.NewSimpleRenderer(t.holder)
 }
@@ -49,6 +52,34 @@ func (t *ThemeOverride) Refresh() {
 		t.holder.Refresh()
 	}
 
-	cache.OverrideTheme(t.Content, t.Theme)
+	cache.OverrideTheme(t.Content, addFeatures(t.Theme, t))
 	t.BaseWidget.Refresh()
 }
+
+// SetDeviceIsMobile allows a ThemeOverride container to shape the contained widgets as a mobile device.
+// This will impact containers such as AppTabs and DocTabs, and more in the future, to display a layout
+// that would automatically be used for a mobile device runtime.
+//
+// Since: 2.6
+func (t *ThemeOverride) SetDeviceIsMobile(on bool) {
+	t.mobile = on
+	t.BaseWidget.Refresh()
+}
+
+type featureTheme struct {
+	fyne.Theme
+
+	over *ThemeOverride
+}
+
+func addFeatures(th fyne.Theme, o *ThemeOverride) fyne.Theme {
+	return &featureTheme{Theme: th, over: o}
+}
+
+func (f *featureTheme) Feature(n intTheme.FeatureName) any {
+	if n == intTheme.FeatureNameDeviceIsMobile {
+		return f.over.mobile
+	}
+
+	return nil
+}

internal/theme/feature.go

@@ -0,0 +1,33 @@
+package theme
+
+import (
+	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/internal/cache"
+)
+
+type FeatureName string
+
+const FeatureNameDeviceIsMobile = FeatureName("deviceIsMobile")
+
+// FeatureTheme defines the method to look up features that we use internally to apply functional
+// differences through a theme override.
+//
+// Since: 2.6
+type FeatureTheme interface {
+	Feature(FeatureName) any
+}
+
+// FeatureForWidget looks up the specified feature flag for the requested widget using the current theme.
+// This is for internal purposes and will do nothing if the theme has not been overridden with the
+// ThemeOverride container.
+//
+// Since: 2.6
+func FeatureForWidget(name FeatureName, w fyne.Widget) any {
+	if custom := cache.WidgetTheme(w); custom != nil {
+		if f, ok := custom.(FeatureTheme); ok {
+			return f.Feature(name)
+		}
+	}
+
+	return nil
+}