实现应用程序在Notification在标题栏提醒

public class Main extends Activity
{
 private NotificationManager notificationManager;
 private Notification notification;
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        notification = new Notification(R.drawable.ic_launcher, "", System.currentTimeMillis());

        Log.d("11111111111", "Oncreate");          
    }
  
 public boolean onKeyDown(int keyCode, KeyEvent event)
 {

     if(keyCode == KeyEvent.KEYCODE_BACK )
     {
      showDialog();//调用退出对话框
      Log.d("back", "back");
     }
     return super.onKeyDown(keyCode, event);
 }

    /**如果用户按下home键，会调用onStop()。发送一个通知。通过这个通知就可以回到原来的界面，而不会调用onCreate方法*/
    @Override
 protected void onStop()
 {
  Intent notificationIntent = new Intent(Main.this, Main.class);//这个实际上只是指定启动一个Activity，这里选择本身
  notificationIntent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
  PendingIntent contentIntent = PendingIntent.getActivity(this, 0, notificationIntent, PendingIntent.FLAG_UPDATE_CURRENT);
  notification.flags = Notification.FLAG_ONGOING_EVENT;//这个表示“正在进行的”，而不是“通知”
  notification.setLatestEventInfo(this, "哇哈哈","哥在运行中...", contentIntent);
  notificationManager.notify(R.drawable.ic_launcher, notification);
  
  Log.d("111111111", "onStop");

  super.onStop();
 }
 
    /**  重新获得焦点的时候清理notification*/
    @Override
 protected void onResume()
 {
  notificationManager.cancelAll();
  super.onResume();
 }

 /**  创建一个对话框，确认是否退出*/
 private void showDialog()
 {
  new AlertDialog.Builder(this).setTitle("是否退出应用程序？")
  .setPositiveButton("确定", new DialogInterface.OnClickListener(){
   
   @Override
   public void onClick(DialogInterface dialog, int which) {
     //finish();//如果这里执行的是finish(),则也会调用onStop()
    android.os.Process.killProcess(android.os.Process.myPid());//整个结束掉，这样就不会执行onStop()
   }
  }).setNegativeButton("取消", new DialogInterface.OnClickListener() {
   
   @Override
   public void onClick(DialogInterface dialog, int which) {
    
   }
  }).show();
 }

 
}