Please note that if you are already using dynamic colors, contrast will be applied + * automatically on Android U+. This is only needed if you have a branded or custom theme and want + * to support contrast. + */ +public class ColorContrast { + + private static final float MEDIUM_CONTRAST_THRESHOLD = 1 / 3f; + private static final float HIGH_CONTRAST_THRESHOLD = 2 / 3f; + + private ColorContrast() {} + + /** + * Applies contrast to all activities by registering a {@link ActivityLifecycleCallbacks} to your + * application. + * + *
A normal usage of this method should happen only once in {@link Application#onCreate()} or + * any methods that run before any of your activities are created. For example: + * + *
+ * public class YourApplication extends Application {
+ * @Override
+ * public void onCreate() {
+ * super.onCreate();
+ * ColorContrast.applyToActivitiesIfAvailable(this);
+ * }
+ * }
+ *
+ *
+ * This method will try to apply a theme overlay in every activity's {@link + * ActivityLifecycleCallbacks#onActivityPreCreated(Activity, Bundle)} callback. + * + * @param application The target application. + * @param colorContrastOptions The color contrast options object that specifies the theme overlay + * resource IDs for medium and high contrast mode. + */ + public static void applyToActivitiesIfAvailable( + @NonNull Application application, @NonNull ColorContrastOptions colorContrastOptions) { + if (!isContrastAvailable()) { + return; + } + + application.registerActivityLifecycleCallbacks( + new ColorContrastActivityLifecycleCallbacks(colorContrastOptions)); + } + + /** + * Applies contrast to the given activity. + * + *
Note that this method does not guarantee the consistency of contrast throughout the app. If + * you want contrast to be updated automatically when a different contrast level is selected in + * the system, please use #applyToActivitiesIfAvailable(Application, ColorContrastOptions). + * + * @param activity The target activity. + * @param colorContrastOptions The color contrast options object that specifies the theme overlay + * resource IDs for medium and high contrast mode. + */ + public static void applyToActivityIfAvailable( + @NonNull Activity activity, @NonNull ColorContrastOptions colorContrastOptions) { + if (!isContrastAvailable()) { + return; + } + + int themeOverlayResourcesId = getContrastThemeOverlayResourceId(activity, colorContrastOptions); + if (themeOverlayResourcesId != 0) { + ThemeUtils.applyThemeOverlay(activity, themeOverlayResourcesId); + } + } + + /** + * Wraps the given context with the theme overlay where color resources are updated. The returned + * context can be used to create views with contrast support. + * + *
Note that this method does not guarantee the consistency of contrast throughout the app. If
+ * you want contrast to be updated automatically when a different contrast level is selected in
+ * the system, please use #applyToActivitiesIfAvailable(Application, ColorContrastOptions).
+ *
+ * @param context The target context.
+ * @param colorContrastOptions The color contrast options object that specifies the theme overlay
+ * resource IDs for medium and high contrast mode.
+ */
+ @NonNull
+ public static Context wrapContextIfAvailable(
+ @NonNull Context context, @NonNull ColorContrastOptions colorContrastOptions) {
+ if (!isContrastAvailable()) {
+ return context;
+ }
+
+ int themeOverlayResourcesId = getContrastThemeOverlayResourceId(context, colorContrastOptions);
+ if (themeOverlayResourcesId == 0) {
+ return context;
+ }
+ return new ContextThemeWrapper(context, themeOverlayResourcesId);
+ }
+
+ /** Returns {@code true} if contrast control is available on the current SDK level. */
+ @ChecksSdkIntAtLeast(api = VERSION_CODES.UPSIDE_DOWN_CAKE)
+ public static boolean isContrastAvailable() {
+ return BuildCompat.isAtLeastU();
+ }
+
+ private static int getContrastThemeOverlayResourceId(
+ Context context, ColorContrastOptions colorContrastOptions) {
+ UiModeManager uiModeManager = (UiModeManager) context.getSystemService(Context.UI_MODE_SERVICE);
+ if (!isContrastAvailable() || uiModeManager == null) {
+ return 0;
+ }
+
+ float currentContrast = uiModeManager.getContrast();
+ int mediumContrastThemeOverlay = colorContrastOptions.getMediumContrastThemeOverlay();
+ int highContrastThemeOverlay = colorContrastOptions.getHighContrastThemeOverlay();
+ if (currentContrast >= HIGH_CONTRAST_THRESHOLD) {
+ // Falls back to mediumContrastThemeOverlay if highContrastThemeOverlay is not set in
+ // ColorContrastOptions. If mediumContrastThemeOverlay is not set, default 0 will be returned.
+ return highContrastThemeOverlay == 0 ? mediumContrastThemeOverlay : highContrastThemeOverlay;
+ } else if (currentContrast >= MEDIUM_CONTRAST_THRESHOLD) {
+ // Falls back to highContrastThemeOverlay if mediumContrastThemeOverlay is not set in
+ // ColorContrastOptions. If highContrastThemeOverlay is not set, default 0 will be returned.
+ return mediumContrastThemeOverlay == 0
+ ? highContrastThemeOverlay
+ : mediumContrastThemeOverlay;
+ }
+ return 0;
+ }
+
+ @RequiresApi(VERSION_CODES.UPSIDE_DOWN_CAKE)
+ private static class ColorContrastActivityLifecycleCallbacks
+ implements ActivityLifecycleCallbacks {
+
+ private final Set An example of the provided theme overlay resource ids could be one of the following:
+ *
+ *
+ *
+ */
+public class ColorContrastOptions {
+
+ @StyleRes private final int mediumContrastThemeOverlayResourceId;
+
+ @StyleRes private final int highContrastThemeOverlayResourceId;
+
+ private ColorContrastOptions(Builder builder) {
+ this.mediumContrastThemeOverlayResourceId = builder.mediumContrastThemeOverlayResourceId;
+ this.highContrastThemeOverlayResourceId = builder.highContrastThemeOverlayResourceId;
+ }
+
+ /** Returns the resource id of the medium contrast theme overlay. */
+ @StyleRes
+ public int getMediumContrastThemeOverlay() {
+ return mediumContrastThemeOverlayResourceId;
+ }
+
+ /** Returns the resource id of the high contrast theme overlay. */
+ @StyleRes
+ public int getHighContrastThemeOverlay() {
+ return highContrastThemeOverlayResourceId;
+ }
+
+ /** Builder class for specifying options when applying contrast. */
+ public static class Builder {
+
+ @StyleRes private int mediumContrastThemeOverlayResourceId;
+
+ @StyleRes private int highContrastThemeOverlayResourceId;
+
+ /** Sets the resource id of the medium contrast theme overlay. */
+ @NonNull
+ @CanIgnoreReturnValue
+ public Builder setMediumContrastThemeOverlay(
+ @StyleRes int mediumContrastThemeOverlayResourceId) {
+ this.mediumContrastThemeOverlayResourceId = mediumContrastThemeOverlayResourceId;
+ return this;
+ }
+
+ /** Sets the resource id of the high contrast theme overlay. */
+ @NonNull
+ @CanIgnoreReturnValue
+ public Builder setHighContrastThemeOverlay(@StyleRes int highContrastThemeOverlayResourceId) {
+ this.highContrastThemeOverlayResourceId = highContrastThemeOverlayResourceId;
+ return this;
+ }
+
+ @NonNull
+ public ColorContrastOptions build() {
+ return new ColorContrastOptions(this);
+ }
+ }
+}