fix(android): reset background color when it becomes transparent or is removed

When a view can use the outline provider (no border width, image,
clip-path or box shadow, e.g. a label with only a border-radius),
`_applyBackground` only applied the color when its native value was
truthy. `transparent` is 0 and a removed color is undefined, so the
previously set ColorDrawable was kept: toggling a class that sets a
background-color left the old color on screen.

Apply any defined color (including transparent) and restore the default
background (or clear the drawable fill) when the color is removed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: farfromrefug

apps/automated/src/ui/view/view-tests.android.ts

@@ -324,6 +324,66 @@ export function testSetAndRemoveBackgroundColor() {
 	});
 }
 
+function getNativeBackgroundColor(v: View): number {
+	const drawable = (<android.view.View>v.android).getBackground();
+	if (drawable instanceof org.nativescript.widgets.BorderDrawable) {
+		return drawable.getBackgroundColor();
+	} else if (drawable instanceof android.graphics.drawable.ColorDrawable) {
+		return drawable.getColor();
+	}
+
+	return drawable ? undefined : 0;
+}
+
+export function testSetTransparentAndRemoveBackgroundColorWithBorderRadius() {
+	const lbl = new Label();
+	lbl.text = 'segment';
+	lbl.borderRadius = 8;
+	lbl.backgroundColor = new Color('red');
+	helper.buildUIAndRunTest(lbl, function (views: Array<View>) {
+		helper.waitUntilLayoutReady(lbl);
+		TKUnit.assertEqual(getNativeBackgroundColor(lbl), new Color('red').android, 'BackgroundColor not applied correctly!');
+
+		lbl.backgroundColor = new Color('transparent');
+		TKUnit.assertEqual(getNativeBackgroundColor(lbl), 0, 'transparent BackgroundColor not applied!');
+
+		lbl.backgroundColor = new Color('red');
+		TKUnit.assertEqual(getNativeBackgroundColor(lbl), new Color('red').android, 'BackgroundColor not applied correctly!');
+
+		lbl.backgroundColor = unsetValue;
+		TKUnit.assertEqual(getNativeBackgroundColor(lbl), 0, 'BackgroundColor not removed!');
+	});
+}
+
+export function testToggleClassBackgroundColorFromCssVariableWithBorderRadius() {
+	const stack = new StackLayout();
+	stack.className = 'segments';
+	stack.css = `
+	.segments { --tile-color: red; }
+	.segment { border-radius: 8; background-color: transparent; }
+	.segment-selected { background-color: var(--tile-color); }
+	.no-transparent-segment { border-radius: 8; }
+	`;
+	const lbl = new Label();
+	lbl.text = 'segment';
+	lbl.className = 'segment segment-selected';
+	stack.addChild(lbl);
+	helper.buildUIAndRunTest(stack, function (views: Array<View>) {
+		helper.waitUntilLayoutReady(lbl);
+		const red = new Color('red').android;
+		TKUnit.assertEqual(getNativeBackgroundColor(lbl), red, 'selected BackgroundColor not applied!');
+
+		lbl.className = 'segment';
+		TKUnit.assertEqual(getNativeBackgroundColor(lbl), 0, 'BackgroundColor should be transparent after deselection!');
+
+		lbl.className = 'no-transparent-segment segment-selected';
+		TKUnit.assertEqual(getNativeBackgroundColor(lbl), red, 'selected BackgroundColor not applied!');
+
+		lbl.className = 'no-transparent-segment';
+		TKUnit.assertEqual(getNativeBackgroundColor(lbl), 0, 'BackgroundColor should be reset after deselection!');
+	});
+}
+
 export function testBackgroundImage() {
 	const lbl = _createLabelWithBorder();
 	lbl.className = 'myClass';

packages/core/ui/core/view/index.android.ts

@@ -1283,13 +1283,14 @@ export class View extends ViewCommon {
 		const nativeView = this.nativeViewProtected as NativeScriptAndroidView;
 		const canUseOutlineProvider = !background.hasBorderWidth() && !background.hasBoxShadows() && !background.clipPath && !background.image && SDK_VERSION >= 21 && (SDK_VERSION >= 33 || background.hasUniformBorderRadius());
 		if (onlyColor || canUseOutlineProvider) {
-			const backgroundColor = background.color?.android;
 			if (isBorderDrawable) {
 				// We need to duplicate the drawable or we lose the "default" cached drawable
 				backgroundDrawable = nativeView._cachedDrawable != null ? AndroidHelper.getCopyOrDrawable(nativeView._cachedDrawable, nativeView.getResources()) : null;
 				nativeView.setBackground(backgroundDrawable);
 			}
-			if (backgroundColor) {
+			// do not test the native color for truthiness: `transparent` is 0
+			if (background.color) {
+				const backgroundColor = background.color.android;
 				if (this.needsNativeDrawableFill && backgroundDrawable) {
 					backgroundDrawable.mutate();
 
@@ -1298,6 +1299,19 @@ export class View extends ViewCommon {
 				} else {
 					nativeView.setBackgroundColor(backgroundColor);
 				}
+			} else if (!isBorderDrawable && background.clearFlags & BackgroundClearFlags.CLEAR_BACKGROUND_COLOR) {
+				// background color was removed: restore the default background
+				if (this.needsNativeDrawableFill && backgroundDrawable) {
+					backgroundDrawable.mutate();
+
+					AndroidHelper.clearDrawableColor(backgroundDrawable);
+					backgroundDrawable.invalidateSelf();
+				} else {
+					const defaultDrawable = nativeView._cachedDrawable ?? null;
+					if (backgroundDrawable !== defaultDrawable) {
+						nativeView.setBackground(defaultDrawable);
+					}
+				}
 			}
 			// borderDrawable is slow
 			// let s use outline provider when we can