Add the preference controller to control accessibility button preview preference

* Create FloatingMenuLayerDrawable class to handle the preview layer drawable

Bug: 173940869
Test: atest AccessibilityButtonPreviewPreferenceControllerTest FloatingMenuLayerDrawableTest
Change-Id: Ia3d030547b377e87c505b2310f559f7f3876ecd5

src/com/android/settings/accessibility/FloatingMenuLayerDrawable.java

@@ -0,0 +1,133 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.accessibility;
+
+import android.content.Context;
+import android.graphics.drawable.Drawable;
+import android.graphics.drawable.LayerDrawable;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.VisibleForTesting;
+
+import com.android.settings.R;
+
+import java.util.Objects;
+
+/** LayerDrawable that contains device icon as background and floating menu icon as foreground. */
+public class FloatingMenuLayerDrawable extends LayerDrawable {
+
+    private FloatingMenuLayerDrawableState mState;
+
+    /**
+     * Creates a new layer drawable with the list of specified layers.
+     *
+     * @param layers a list of drawables to use as layers in this new drawable,
+     *               must be non-null
+     */
+    private FloatingMenuLayerDrawable(@NonNull Drawable[] layers) {
+        super(layers);
+    }
+
+    /**
+     * Create the {@link LayerDrawable} that contains device icon as background and floating menu
+     * icon with given {@code opacity} value as foreground.
+     *
+     * @param context the valid context used to get the icon
+     * @param resId the resource ID of the floating menu icon
+     * @param opacity the opacity to apply to the given icon
+     * @return the drawable that combines the device icon and the floating menu icon
+     */
+    public static FloatingMenuLayerDrawable createLayerDrawable(Context context, int resId,
+            int opacity) {
+        final Drawable bg = context.getDrawable(R.drawable.accessibility_button_preview_base);
+        final FloatingMenuLayerDrawable basicDrawable = new FloatingMenuLayerDrawable(
+                new Drawable[]{bg, null});
+
+        basicDrawable.updateLayerDrawable(context, resId, opacity);
+        return basicDrawable;
+    }
+
+    /**
+     * Update the drawable  with given {@code resId} drawable and {@code opacity}(alpha)
+     * value at index 1 layer.
+     *
+     * @param context the valid context used to get the icon
+     * @param resId the resource ID of the floating menu icon
+     * @param opacity the opacity to apply to the given icon
+     */
+    public void updateLayerDrawable(Context context, int resId, int opacity) {
+        final Drawable icon = context.getDrawable(resId);
+        icon.setAlpha(opacity);
+        this.setDrawable(/* index= */ 1, icon);
+        this.setConstantState(context, resId, opacity);
+    }
+
+    @Override
+    public ConstantState getConstantState() {
+        return mState;
+    }
+
+    /** Stores the constant state and data to the given drawable. */
+    private void setConstantState(Context context, int resId, int opacity) {
+        mState = new FloatingMenuLayerDrawableState(context, resId, opacity);
+    }
+
+    /** {@link ConstantState} to store the data of {@link FloatingMenuLayerDrawable}. */
+    @VisibleForTesting
+    static class FloatingMenuLayerDrawableState extends ConstantState {
+
+        private final Context mContext;
+        private final int mResId;
+        private final int mOpacity;
+
+        FloatingMenuLayerDrawableState(Context context, int resId, int opacity) {
+            mContext = context;
+            mResId = resId;
+            mOpacity = opacity;
+        }
+
+        @NonNull
+        @Override
+        public Drawable newDrawable() {
+            return createLayerDrawable(mContext, mResId, mOpacity);
+        }
+
+        @Override
+        public int getChangingConfigurations() {
+            return 0;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) {
+                return true;
+            }
+            if (o == null || getClass() != o.getClass()) {
+                return false;
+            }
+            final FloatingMenuLayerDrawableState that = (FloatingMenuLayerDrawableState) o;
+            return mResId == that.mResId
+                    && mOpacity == that.mOpacity
+                    && Objects.equals(mContext, that.mContext);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(mContext, mResId, mOpacity);
+        }
+    }
+}