BackgroundManager.java

package com.prateekj.snooper.infra;


import android.app.Activity;
import android.app.Application;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;

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

public class BackgroundManager implements Application.ActivityLifecycleCallbacks {

  private static final long BACKGROUND_DELAY = 500;
  private static final String TAG = BackgroundManager.class.getSimpleName();

  private static BackgroundManager sInstance;

  public interface Listener {
    void onBecameForeground();

    void onBecameBackground();
  }

  private boolean mInBackground = true;
  private final List<Listener> listeners = new ArrayList<>();
  private final Handler mBackgroundDelayHandler = new Handler();
  private Runnable mBackgroundTransition;

  private BackgroundManager(Application application) {
    application.registerActivityLifecycleCallbacks(this);
  }

  public static BackgroundManager getInstance(Application application) {
    if (sInstance == null) {
      sInstance = new BackgroundManager(application);
    }
    return sInstance;
  }


  public void registerListener(Listener listener) {
    listeners.add(listener);
  }

  public void unregisterListener(Listener listener) {
    listeners.remove(listener);
  }

  public boolean isInBackground() {
    return mInBackground;
  }

  @Override
  public void onActivityResumed(Activity activity) {
    if (mBackgroundTransition != null) {
      mBackgroundDelayHandler.removeCallbacks(mBackgroundTransition);
      mBackgroundTransition = null;
    }

    if (mInBackground) {
      mInBackground = false;
      notifyOnBecameForeground();
      Log.d(TAG, "Application went to foreground");
    }
  }

  private void notifyOnBecameForeground() {
    for (Listener listener : listeners) {
      try {
        listener.onBecameForeground();
      } catch (Exception e) {
        Log.d(TAG, "Listener threw exception!", e);
      }
    }
  }

  @Override
  public void onActivityPaused(Activity activity) {
    if (!mInBackground && mBackgroundTransition == null) {
      mBackgroundTransition = new Runnable() {
        @Override
        public void run() {
          mInBackground = true;
          mBackgroundTransition = null;
          notifyOnBecameBackground();
          Log.d(TAG, "Application went to background");
        }
      };
      mBackgroundDelayHandler.postDelayed(mBackgroundTransition, BACKGROUND_DELAY);
    }
  }

  private void notifyOnBecameBackground() {
    for (Listener listener : listeners) {
      try {
        listener.onBecameBackground();
      } catch (Exception e) {
        Log.e(TAG, "Listener threw exception!", e);
      }
    }
  }

  @Override
  public void onActivityStopped(Activity activity) {
  }

  @Override
  public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
  }

  @Override
  public void onActivityStarted(Activity activity) {
  }

  @Override
  public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
  }

  @Override
  public void onActivityDestroyed(Activity activity) {
  }
}