Detailed explanation of ActivityLifecycleCallbacks instance in Android

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/**
  * Demo example:
  * ActivityLifecycleCallbacks usage example
  *
  * ActivityLifecycleCallbacks is used to track and callback the life cycle of an activity in the application
  *
  * Use ActivityLifecycleCallbacks to achieve:
  * 1 Determine whether the app is running in the background
  * 2 Close all activities of the app
  *
  *
  * (1) Determine whether the app is running in the background
  * In this implementation, the activityCounter is used to record the number of activities.
  * Determine whether the current APP is running in the foreground by whether the activityCounter is 0.
  *
  * From the implementation method of ActivityLifecycleCallbacks, our inertial thinking is:
  * ActivityCounter+1 in onActivityResumed() of ActivityLifecycleCallbacks.
  * activityCounter-1 in onActivityPaused(),
  * But is that right? 
  *
  * Let's first look at the life cycles of two activities when the interface jumps
  * When jumping from Activity A to Activity B, the life cycles of the two activities are as follows:
  * ()->()->()-> ()-> ()-> ()
  *
  * If as follows:
  * ActivityCounter=1 after A starts;
  * Execute when calling() when jumping from A to B: activityCounter-1=0;
  * That is, the APP is running in the background.
  * Of course this is wrong. The APP is of course running in the foreground during the switching of the two interfaces. 
  *
  * Modifications as follows:
  * In onActivityStarted() for activityCounter+1
  * For activityCounter-1 in onActivityStopped()
  * Summary: Pay attention to the life cycle when the Activity jumps
  *
  * (2) Close all activities of the application
  * 2.1 Use LinkedList<Activity> to manage the interface in the application
  * 2.2 onActivityCreated() in ActivityLifecycleCallbacks
  * Add Activity to LinkedList
  * onActivityDestroyed() in ActivityLifecycleCallbacks
  * Remove Activity from LinkedList
  * 2.3 Destroy all activities in LinkedList when closing the application
  *
  * Note description:
  * 1 ActivityLifecycleCallbacks is only available in API 14 and above
  * 2 Under Android 4.0, you can implement this idea in BaseActivity
  *
  */ 
public class MyApplication extends Application { 
  private static int activityCounter=0; 
  private static MyApplication mApplicationInstance; 
  private static LinkedList&lt;Activity&gt; mActivityLinkedList; 
  private ActivityLifecycleCallbacksImpl mActivityLifecycleCallbacksImpl; 
  @Override 
  public void onCreate() { 
    (); 
    mApplicationInstance=new MyApplication(); 
    mActivityLinkedList=new LinkedList&lt;Activity&gt;(); 
    mActivityLifecycleCallbacksImpl=new ActivityLifecycleCallbacksImpl(); 
    (mActivityLifecycleCallbacksImpl); 
  } 
   
  public static MyApplication getInstance() { 
    if (null==mApplicationInstance) { 
      mApplicationInstance=new MyApplication(); 
    } 
    return mApplicationInstance; 
  } 
   
  //Judge whether the app is running in the background  public boolean isAppRunningBackground(){ 
    boolean flag=false; 
    if(activityCounter==0){ 
      flag=true; 
    } 
    return flag; 
  } 
   
  //Exit the application  public void finishAllActivity(){ 
    //unregisterActivityLifecycleCallbacks(mActivityLifecycleCallbacksImpl); 
    ("--&gt; ()="+()); 
    if(null!=mActivityLinkedList){ 
      for(Activity activity:mActivityLinkedList){ 
        if(null!=activity){ 
          (); 
        } 
      } 
    } 
  } 
   
   
  private class ActivityLifecycleCallbacksImpl implements ActivityLifecycleCallbacks{ 
    @Override 
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) { 
      ("onActivityCreated --&gt; "+().getName()); 
      if (null!=mActivityLinkedList&amp;&amp;null!=activity) { 
        (activity); 
      } 
    } 
 
    @Override 
    public void onActivityStarted(Activity activity) { 
      activityCounter++; 
      ("onActivityStarted --&gt; "+().getName()+",activityCounter="+activityCounter); 
    } 
 
    @Override 
    public void onActivityResumed(Activity activity) { 
      ("onActivityResumed --&gt; "+().getName()); 
    } 
 
    @Override 
    public void onActivityPaused(Activity activity) { 
      ("onActivityPaused --&gt; "+().getName()); 
    } 
 
    @Override 
    public void onActivityStopped(Activity activity) { 
      activityCounter--; 
      ("onActivityStopped --&gt; "+().getName()+",activityCounter="+activityCounter); 
    } 
 
    @Override 
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) { 
      ("onActivitySaveInstanceState --&gt; "+().getName()); 
    } 
 
    @Override 
    public void onActivityDestroyed(Activity activity) { 
      ("onActivityDestroyed --&gt; "+().getName()); 
      if (null!=mActivityLinkedList&amp;&amp;null!=activity) { 
        if ((activity)) { 
          (activity); 
        } 
      } 
    } 
     
  } 
 
} 

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public class FirstActivity extends Activity { 
   private Context mContext; 
   private Button mOpenNewActivityButton; 
   private Button mFinishThisActivityButton; 
   private ClickListenerImpl mClickListenerImpl; 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    (savedInstanceState); 
    setContentView(.first_activity); 
    init(); 
  } 
   
  private void init(){ 
    mContext=this; 
    mClickListenerImpl=new ClickListenerImpl(); 
    mOpenNewActivityButton=(Button) findViewById(); 
    (mClickListenerImpl); 
    mFinishThisActivityButton=(Button) findViewById(); 
    (mClickListenerImpl); 
  } 
   
   
  private class ClickListenerImpl implements OnClickListener { 
    @Override 
    public void onClick(View v) { 
      switch (()) { 
      case : 
        Intent intent=new Intent(mContext, ); 
        startActivity(intent); 
        break; 
      case : 
        finish(); 
        break; 
 
      default: 
        break; 
      } 
 
    } 
 
  } 
   
  @Override 
  protected void onResume() { 
    (); 
    //(" first Activity onResume --> "+().isAppRunningBackground()); 
  } 
   
  @Override 
  protected void onStop() { 
    (); 
    //(" first Activity onStop --> "+().isAppRunningBackground()); 
  } 
   
   
} 

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public class SecondActivity extends Activity { 
   private Context mContext; 
   private Button mOpenNewActivityButton; 
   private Button mFinishThisActivityButton; 
   private ClickListenerImpl mClickListenerImpl; 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    (savedInstanceState); 
    setContentView(.second_activity); 
    init(); 
  } 
   
  private void init(){ 
    mContext=this; 
    mClickListenerImpl=new ClickListenerImpl(); 
    mOpenNewActivityButton=(Button) findViewById(); 
    (mClickListenerImpl); 
    mFinishThisActivityButton=(Button) findViewById(); 
    (mClickListenerImpl); 
  } 
   
   
  private class ClickListenerImpl implements OnClickListener { 
    @Override 
    public void onClick(View v) { 
      switch (()) { 
      case : 
        Intent intent=new Intent(mContext, ); 
        startActivity(intent); 
        break; 
 
      case : 
        finish(); 
        break; 
 
      default: 
        break; 
      } 
 
    } 
 
  } 
 
   
} 

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public class ThirdActivity extends Activity { 
   private Context mContext; 
   private Button mFinishAllActivityButton; 
   private Button mFinishThisActivityButton; 
   private ClickListenerImpl mClickListenerImpl; 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    (savedInstanceState); 
    setContentView(.third_activity); 
    init(); 
  } 
   
  private void init(){ 
    mContext=this; 
    mClickListenerImpl=new ClickListenerImpl(); 
    mFinishThisActivityButton=(Button) findViewById(); 
    (mClickListenerImpl); 
    mFinishAllActivityButton=(Button) findViewById(); 
    (mClickListenerImpl); 
  } 
   
   
  private class ClickListenerImpl implements OnClickListener { 
    @Override 
    public void onClick(View v) { 
      switch (()) { 
      case : 
        finish(); 
        break; 
      case : 
        ().finishAllActivity(); 
        break; 
      default: 
        break; 
      } 
 
    } 
  } 
   
  @Override 
  protected void onResume() { 
    (); 
    //(" third Activity onResume --> "+().isAppRunningBackground()); 
  } 
   
  @Override 
  protected void onStop() { 
    (); 
    //(" third Activity onStop --> "+().isAppRunningBackground()); 
  } 
   
  @Override 
  protected void onDestroy() { 
    (); 
    //(" third Activity onDestroy --> "+().isAppRunningBackground()); 
  } 
 
   
} 

<RelativeLayout xmlns:andro 
  xmlns:tools="/tools" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" 
  android:paddingBottom="@dimen/activity_vertical_margin" 
  android:paddingLeft="@dimen/activity_horizontal_margin" 
  android:paddingRight="@dimen/activity_horizontal_margin" 
  android:paddingTop="@dimen/activity_vertical_margin" 
  tools:context="" > 
 
  <Button 
    android: 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_centerInParent="true" 
    android:text="open new Activity" /> 
 
  <TextView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_above="@id/openNewActivityButton" 
    android:layout_centerInParent="true" 
    android:layout_marginBottom="50dip" 
    android:textSize="20sp" 
    android:textColor="@android:color/holo_red_light" 
    android:text="This is the first Activity" /> 
 
  <Button 
    android: 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_below="@id/openNewActivityButton" 
    android:layout_centerHorizontal="true" 
    android:layout_marginTop="50dip" 
    android:text="finish this activity" /> 
 
</RelativeLayout> 

<RelativeLayout xmlns:andro 
  xmlns:tools="/tools" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" 
  android:paddingBottom="@dimen/activity_vertical_margin" 
  android:paddingLeft="@dimen/activity_horizontal_margin" 
  android:paddingRight="@dimen/activity_horizontal_margin" 
  android:paddingTop="@dimen/activity_vertical_margin" 
  tools:context="" > 
 
  <Button 
    android: 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_centerInParent="true" 
    android:text="open new Activity" /> 
 
  <TextView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_above="@id/openNewActivityButton" 
    android:layout_centerInParent="true" 
    android:layout_marginBottom="50dip" 
    android:textSize="20sp" 
    android:textColor="@android:color/holo_red_light" 
    android:text="This is the second Activity" /> 
 
  <Button 
    android: 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_below="@id/openNewActivityButton" 
    android:layout_centerHorizontal="true" 
    android:layout_marginTop="50dip" 
    android:text="finish this activity" /> 
 
</RelativeLayout> 

<RelativeLayout xmlns:andro 
  xmlns:tools="/tools" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" 
  android:paddingBottom="@dimen/activity_vertical_margin" 
  android:paddingLeft="@dimen/activity_horizontal_margin" 
  android:paddingRight="@dimen/activity_horizontal_margin" 
  android:paddingTop="@dimen/activity_vertical_margin" 
  tools:context="" > 
 
  <TextView 
    android: 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_above="@id/openNewActivityButton" 
    android:layout_centerHorizontal="true" 
    android:layout_marginTop="100dp" 
    android:text="This is the third Activity" 
    android:textColor="@android:color/holo_red_light" 
    android:textSize="20sp" /> 
 
  <Button 
    android: 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_below="@id/textView" 
    android:layout_centerHorizontal="true" 
    android:layout_marginTop="50dip" 
    android:text="finish this activity" /> 
 
  <Button 
    android: 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_below="@id/finishThisActivityButton" 
    android:layout_centerHorizontal="true" 
    android:layout_marginTop="50dip" 
    android:text="finish All Activity" /> 
 
</RelativeLayout> 

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:andro 
  package="" 
  android:versionCode="1" 
  android:versionName="1.0" > 
 
  <uses-sdk 
    android:minSdkVersion="14" 
    android:targetSdkVersion="14" /> 
 
  <application 
    android:name="" 
    android:allowBackup="true" 
    android:icon="@drawable/ic_launcher" 
    android:label="@string/app_name" 
    android:theme="@style/AppTheme" > 
    <activity 
      android:name=".FirstActivity" 
      android:label="@string/app_name" > 
      <intent-filter> 
        <action android:name="" /> 
 
        <category android:name="" /> 
      </intent-filter> 
    </activity> 
     
    <activity android:name=""/> 
    <activity android:name=""/> 
  </application> 
 
</manifest>