@Override 
  protected void onStop() { 
  // TODO Auto-generated method stub 
  　　super.onStop(); 
  　　Log.v("BACKGROUND", "程序进入后台"); 
  　　showNotification(); 
  } 

// 点击HOME键时程序进入后台运行 
 
  @Override 
 
  public boolean onKeyDown(int keyCode, KeyEvent event) { 
 
    // TODO Auto-generated method stub 
 
    // 按下HOME键 
 
    if(keyCode == KeyEvent.KEYCODE_HOME){ 
 
      // 显示Notification 
 
      notification = new NotificationExtend(this); 
 
      notification.showNotification(); 
 
      moveTaskToBack(true);         

      return true; 
 
    } 
 
    return super.onKeyDown(keyCode, event); 
 
  } 

package com.test.background; 

import android.app.Activity; 
 
import android.app.Notification; 
 
import android.app.NotificationManager; 
 
import android.app.PendingIntent; 
 
import android.content.Intent; 
 
import android.graphics.Color; 

/** 
 * Notification扩展类 
 * @Description: Notification扩展类 
 * @File: NotificationExtend.java 
 * @Package com.test.background 
 */ 
 
public class NotificationExtend { 
 
  private Activity context; 

  public NotificationExtend(Activity context) { 
 
    // TODO Auto-generated constructor stub 
 
    this.context = context; 
 
  } 
 
  // 显示Notification 
 
  public void showNotification() { 
 
    // 创建一个NotificationManager的引用 
 
    NotificationManager notificationManager = ( 
 
        NotificationManager)context.getSystemService( 
 
            android.content.Context.NOTIFICATION_SERVICE); 
 
    // 定义Notification的各种属性 
 
    Notification notification = new Notification( 
 
        R.drawable.icon,"阅读器",  
 
        System.currentTimeMillis()); 
 
    // 将此通知放到通知栏的"Ongoing"即"正在运行"组中 
 
    notification.flags |= Notification.FLAG_ONGOING_EVENT; 
 
    // 表明在点击了通知栏中的"清除通知"后，此通知自动清除。 
 
    notification.flags |= Notification.FLAG_AUTO_CANCEL 
 
    notification.flags |= Notification.FLAG_SHOW_LIGHTS; 
 
    notification.defaults = Notification.DEFAULT_LIGHTS; 
 
    notification.ledARGB = Color.BLUE; 
 
    notification.ledOnMS = 5000; 

    // 设置通知的事件消息 
 
    CharSequence contentTitle = "阅读器显示信息"; // 通知栏标题 
 
    CharSequence contentText = "推送信息显示，请查看……"; // 通知栏内容 

    Intent notificationIntent = new Intent(context,context.getClass()); 
 
    notificationIntent.setAction(Intent.ACTION_MAIN); 
    notificationIntent.addCategory(Intent.CATEGORY_LAUNCHER); 
    PendingIntent contentIntent = PendingIntent.getActivity( 
    context, 0, notificationIntent,PendingIntent.FLAG_UPDATE_CURRENT); 
    notification.setLatestEventInfo( 
    context, contentTitle, contentText, contentIntent); 
    // 把Notification传递给NotificationManager 
    notificationManager.notify(0, notification); 
 
  } 

  // 取消通知 
 
  public void cancelNotification(){ 
 
    NotificationManager notificationManager = ( 
 
        NotificationManager) context.getSystemService( 
 
            android.content.Context.NOTIFICATION_SERVICE); 
 
    notificationManager.cancel(0); 
 
  } 
 
} 

<activity android:name="ShowMessageActivity" 
       android:launchMode="singleTask"></activity>  

public class MyApplication extends Application{ 
  public int count = 0; 
  @Override 
  public void onCreate() { 
    super.onCreate(); 
 
    registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() { 
 
      @Override 
      public void onActivityStopped(Activity activity) { 
        Log.v("viclee", activity + "onActivityStopped"); 
        count--; 
        if (count == 0) { 
          Log.v("viclee", ">>>>>>>>>>>>>>>>>>>切到后台 lifecycle"); 
        } 
      } 
 
      @Override 
      public void onActivityStarted(Activity activity) { 
        Log.v("viclee", activity + "onActivityStarted"); 
        if (count == 0) { 
          Log.v("viclee", ">>>>>>>>>>>>>>>>>>>切到前台 lifecycle"); 
        } 
        count++; 
      } 
 
      @Override 
      public void onActivitySaveInstanceState(Activity activity, Bundle outState) { 
        Log.v("viclee", activity + "onActivitySaveInstanceState"); 
      } 
 
      @Override 
      public void onActivityResumed(Activity activity) { 
        Log.v("viclee", activity + "onActivityResumed"); 
      } 
 
      @Override 
      public void onActivityPaused(Activity activity) { 
        Log.v("viclee", activity + "onActivityPaused"); 
      } 
 
      @Override 
      public void onActivityDestroyed(Activity activity) { 
        Log.v("viclee", activity + "onActivityDestroyed"); 
      } 
 
      @Override 
      public void onActivityCreated(Activity activity, Bundle savedInstanceState) { 
        Log.v("viclee", activity + "onActivityCreated"); 
      } 
    }); 
  } 
} 

//用来控制应用前后台切换的逻辑 
 private boolean isCurrentRunningForeground = true; 
 @Override 
 protected void onStart() { 
   super.onStart(); 
   if (!isCurrentRunningForeground) { 
     Log.d(TAG, ">>>>>>>>>>>>>>>>>>>切到前台 activity process"); 
   } 
 } 
 
 @Override 
 protected void onStop() { 
   super.onStop(); 
   isCurrentRunningForeground = isRunningForeground(); 
   if (!isCurrentRunningForeground) { 
     Log.d(TAG,">>>>>>>>>>>>>>>>>>>切到后台 activity process"); 
   } 
 } 
 
 public boolean isRunningForeground() { 
   ActivityManager activityManager = (ActivityManager) this.getSystemService(Context.ACTIVITY_SERVICE); 
   List<ActivityManager.RunningAppProcessInfo> appProcessInfos = activityManager.getRunningAppProcesses(); 
   // 枚举进程 
   for (ActivityManager.RunningAppProcessInfo appProcessInfo : appProcessInfos) { 
     if (appProcessInfo.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND) { 
       if (appProcessInfo.processName.equals(this.getApplicationInfo().processName)) { 
         Log.d(TAG,"EntryActivity isRunningForeGround"); 
         return true; 
       } 
     } 
   } 
   Log.d(TAG, "EntryActivity isRunningBackGround"); 
   return false; 
 }