android怎么判断程序在后台运行，让后台将程序图标显示在状态栏上？

根据activity的生命周期，在activity不显示时，会执行onStop函数，所以你在onStop函数（按退出键除外）里面把notification放在通知栏里，再此显示时，把notification从通知栏里去掉。 

或者，只要程序在运行就一直显示通知栏图标，这样简单点。 

        privatevoid 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, 
                "天籁之音播放器", System.currentTimeMillis()); 
        notification.flags |= Notification.FLAG_ONGOING_EVENT; // 将此通知放到通知栏的"Ongoing"即"正在运行"组中 
        notification.flags |= Notification.FLAG_NO_CLEAR; // 表明在点击了通知栏中的"清除通知"后，此通知不清除，经常与FLAG_ONGOING_EVENT一起使用 
        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 ="天籁之音正在播放……"; // 通知栏标题 
        CharSequence contentText ="ameyume"; // 通知栏内容 
        Intent notificationIntent =new Intent(context, MusicDemo.class); // 点击该通知后要跳转的Activity 
        PendingIntent contentItent = PendingIntent.getActivity(context, 0, 
                notificationIntent, 0); 
        notification.setLatestEventInfo(context, contentTitle, contentText, 
                contentItent); 

        // 把Notification传递给NotificationManager 
        notificationManager.notify(0, notification); 
    } 

去掉通知栏通知的方法 

            // 启动后删除之前我们定义的通知 
            N
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otificationManager notificationManager = (NotificationManager) this 
                    .getSystemService(NOTIFICATION_SERVICE); 
            notificationManager.cancel(0);