Android判断程序前后台状态

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;
    }
}