Android推断程序前后台状态

public class AppStatusService extends Service { 
    private static final String TAG = "AppStatusService"; 
    private ActivityManager activityManager; 
    private String packageName; 
 
    @Override 
    public IBinder onBind(Intent intent) { 
        return null; 
    } 
 
    @Override 
    public int onStartCommand(Intent intent, int flags, int startId) { 
        activityManager = (ActivityManager) this.getSystemService(Context.ACTIVITY_SERVICE); 
        packageName = this.getPackageName(); 
        new Thread() { 
            public void run() { 
                try { 
                    while (true) { 
                        Thread.sleep(1000); 
                        if (isAppOnForeground()) { 
                            Log.i(TAG, "true"); 
                        } else { 
                            Log.i(TAG, "false"); 
                        } 
                    } 
                } catch (Exception e) { 
                    e.printStackTrace(); 
                } 
            } 
        }.start(); 
        return super.onStartCommand(intent, flags, startId); 
    } 
 
    private boolean isAppOnForeground() { 
        // Returns a list of application processes that are running on the device 
        List<RunningAppProcessInfo> appProcesses = activityManager.getRunningAppProcesses(); 
        if (appProcesses == null) return false; 
        for (RunningAppProcessInfo appProcess : appProcesses) { 
            // importance: 
            // The relative importance level that the system places  
            // on this process. 
            // May be one of IMPORTANCE_FOREGROUND, IMPORTANCE_VISIBLE,  
            // IMPORTANCE_SERVICE, IMPORTANCE_BACKGROUND, or IMPORTANCE_EMPTY. 
            // These constants are numbered so that "more important" values are 
            // always smaller than "less important" values. 
            // processName: 
            // The name of the process that this object is associated with. 
            if (appProcess.processName.equals(packageName) 
                    && appProcess.importance == RunningAppProcessInfo.IMPORTANCE_FOREGROUND) { 
                return true; 
            } 
        } 
        return false; 
    } 
}