android Notification
    是显示在手机状态栏上的通知,具有全局效果的通知
    时效性不强
    
    步骤:
    // 获得系统服务
    NotificationManager mNotificationManager
   = (NotificationManager)getSystemService(Context.NOTIFICATION_SERVICE);
    
    // 创建一个Notification对象
    Notification notification = new Notification(R.drawable.ic_launcher,
            “短信来了”, System.currentTimeMillis());
    // 设置点击事件关联activity
    Intent intent = new Intent(this, SecondActivity.class);
    PendingIntent contentIntent = PendingIntent.getActivity(this, 0,intent, 0);
    // 设置标题跟内容
    notification.setLatestEventInfo(this, “小丽”, “在么”, contentIntent);
    // 发送通知
    mNotificationManager.notify(0, notification);                

    
    // 点击之后,消失
    //  notification.flags = Notification.FLAG_AUTO_CANCEL;
    // 点击之后,不会消失
        notification.flags = Notification.FLAG_ONGOING_EVENT;

    
    取消通知:
    mNotificationManager.cancel(0);//参数必须是之前发送通知的id