UiChangeDetector.java

/*
 * Copyright (C) 2015 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.switchaccess;

import android.annotation.TargetApi;
import android.os.Build;
import android.view.accessibility.AccessibilityEvent;
import com.android.utils.AccessibilityEventListener;

/**
 * Class to detect possible changes to the UI based on AccessibilityEvents
 */
@TargetApi(Build.VERSION_CODES.LOLLIPOP)
public class UiChangeDetector implements AccessibilityEventListener {
    PossibleUiChangeListener mListener;

    public UiChangeDetector(PossibleUiChangeListener listener) {
        mListener = listener;
    }

    @Override
    public void onAccessibilityEvent(AccessibilityEvent event) {
        if (event == null) {
            return;
        }
        int eventType = event.getEventType();
        boolean willClearFocus = (eventType == AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED)
                || (eventType == AccessibilityEvent.TYPE_WINDOWS_CHANGED)
                || (eventType == AccessibilityEvent.TYPE_VIEW_SCROLLED);

        if (eventType == AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED) {
            /* Ignore changes that don't affect the view hierarchy */
            int changeTypes = event.getContentChangeTypes();
            changeTypes &= ~AccessibilityEvent.CONTENT_CHANGE_TYPE_TEXT;
            changeTypes &= ~AccessibilityEvent.CONTENT_CHANGE_TYPE_CONTENT_DESCRIPTION;
            willClearFocus = (changeTypes != 0);
        }

        if (willClearFocus) {
            mListener.onPossibleChangeToUi();
        }
    }

    public interface PossibleUiChangeListener {
        void onPossibleChangeToUi();
    }
}