Watcher Top Activity

TopActivityWatcher.java

package com.straucorp.core;

import android.app.ActivityManager;
import android.content.ComponentName;
import android.content.Context;
import android.os.Handler;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

/**
 * @author Straube - Created by Andre Straube on 25/03/2020
 *
 * @usage Programmatically
 * TopActivityWatcher watcher = new TopActivityWatcher();
 * watcher.registerListener(listener);
 * watcher.start(this.applicationContext);
 */
public class TopActivityWatcher {

    static final int DEFAULT_TOLERANCE = 1;
    static final int DEFAULT_CHECK_INTERVAL_MS = 500;

    final List<TopActivityListener> mListenerList = new ArrayList<>();
    final Object mResLock = new Object();

    int mCheckIntervalMs;
    int mTolerance;

    String mTopActivity = null;
    String mPendingActivity = null;
    int mPendingCount = 0;

    Handler mHandler = null;
    ActivityManager mActivityManager = null;

    boolean mIsRunning = false;

    Runnable mTopActivityCheckRunnable = new Runnable() {
        @Override
        public void run() {
            String topActivity = getTopActivityClassName();
            if (mTopActivity == null && topActivity != null) {
                updateTopActivity(topActivity);
            }

            else if (!Objects.equals(topActivity, mTopActivity)) {
                if (Objects.equals(topActivity, mPendingActivity)) {
                    mPendingActivity = topActivity;
                    mPendingCount = 1;
                } else {
                    mPendingCount++;
                    if (mPendingCount > mTolerance) {
                        updateTopActivity(topActivity);
                    }
                }
            }

            synchronized (mResLock) {
                if (mHandler != null) {
                    mHandler.postDelayed(this, mCheckIntervalMs);
                }
            }
        }
    };

    public TopActivityWatcher() {
        this(DEFAULT_CHECK_INTERVAL_MS, DEFAULT_TOLERANCE);
    }

    public TopActivityWatcher(int checkIntervalMs, int tolerance) {
        mCheckIntervalMs = checkIntervalMs;
        mTolerance = tolerance;
    }

    public void registerListener(final TopActivityListener aListener) {
        synchronized (mListenerList) {
            if (!mListenerList.contains(aListener)) {
                mListenerList.add(aListener);
            }
        }
    }

    public void unregisterListener(final TopActivityListener aListener) {
        synchronized (mListenerList) {
            if (mListenerList.contains(aListener)) {
                mListenerList.remove(aListener);
            }
        }
    }

    public boolean start(Context context) {
        synchronized (mResLock) {
            if( !mIsRunning ) {
                if (mActivityManager == null) {
                    mActivityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
                }
                if (mActivityManager != null) {
                    if (mHandler == null) {
                        mHandler = new Handler();
                    }
                    mIsRunning = true;
                    mHandler.post(mTopActivityCheckRunnable);
                }
            }
            return mIsRunning;
        }
    }

    public void stop() {
        synchronized (mResLock) {
            if(mIsRunning) {
                if (mActivityManager != null) {
                    mActivityManager = null;
                }
                if (mHandler != null) {
                    mHandler.removeCallbacksAndMessages(null);
                    mHandler = null;
                }
                mIsRunning = false;
            }
        }
    }

    private void notifyTopActivityChanged(final String topActivity) {
        synchronized (mListenerList) {
            for (TopActivityListener listener : mListenerList) {
                if (listener != null) {
                    listener.onTopActivityChanged(topActivity);
                }
            }
        }
    }

    private void updateTopActivity(final String topActivity) {
        if (!Objects.equals(mTopActivity, topActivity)) {
            mTopActivity = topActivity;
            mPendingActivity = null;
            mPendingCount = 0;
            notifyTopActivityChanged(topActivity);
        }
    }

    private String getTopActivityClassName() {
        String topActivity = null;
        List<ActivityManager.RunningTaskInfo> runningTasks = null;

        synchronized (mResLock) {
            if (mActivityManager != null) {
                try {
                    runningTasks = mActivityManager.getRunningTasks(1);
                } catch (SecurityException ex) {
                    ex.printStackTrace();
                }
            }
        }

        if (runningTasks != null && !runningTasks.isEmpty()) {
            ActivityManager.RunningTaskInfo runningTaskInfo = runningTasks.get(0);
            if (runningTaskInfo != null) {
                ComponentName topComponent = runningTaskInfo.topActivity;
                if (topComponent != null) {
                    topActivity = topComponent.getClassName();
                }
            }
        }
        return topActivity;
    }

    public interface TopActivityListener {
        void onTopActivityChanged(final String newActivity);
    }
}