Android获取网速的问题，结果一直是0 KB/s

在网上找了好多获取网速的代码，方法都是差不多的，但是我通过以下代码获得的网速都是0，是哪里出问题了呢？

private Timer myTimer;
private long lastTotalRxBytes = 0;
private long lastTimeStamp = 0;

private void showNetSpeed() {
        long nowTotalRxBytes = getTotalRxBytes();
        long nowTimeStamp = System.currentTimeMillis();
        double speed = (nowTotalRxBytes - lastTotalRxBytes) * 1000 / (nowTimeStamp - lastTimeStamp);

        Log.d("xxx", "showNetSpeed: " + speed);

        lastTimeStamp = nowTimeStamp;
        lastTotalRxBytes = nowTotalRxBytes;

        Message msg = new Message();
        msg.what = 100;
        msg.obj = showSpeed(speed);
        mHandler.sendMessage(msg);
}

private DecimalFormat showFloatFormat = new DecimalFormat("0.00");

private String showSpeed(double speed) {
        String speedString;
        if (speed >= 1048576d) {
                speedString = showFloatFormat.format(speed / 1048576d) + " MB/s";
        } else {
                speedString = showFloatFormat.format(speed / 1024d) + " KB/s";
        }
        return speedString;
}

private long getTotalRxBytes() {
        return TrafficStats.getUidRxBytes(MainActivity.this.getApplicationInfo().uid) == TrafficStats.UNSUPPORTED ?
                        0 : (TrafficStats.getTotalRxBytes() / 1024);//转为KB
}

public void start(View view) {
        if (myTimer != null) {
                myTimer.cancel();
        }
        myTimer = new Timer();
        lastTotalRxBytes = getTotalRxBytes();
        lastTimeStamp = System.currentTimeMillis();
        myTimer.schedule(new TimerTask() {
                @Override
                public void run() {
                        showNetSpeed();
                }
        }, 1000, 1000);
}

public void stop(View view) {
        if (myTimer != null) {
                myTimer.cancel();
        }
}

主要是这一块获取字节的代码问题，得到的结果都是0，我想请问一下是什么原因造成的？

private long getTotalRxBytes() {
        return TrafficStats.getUidRxBytes(MainActivity.this.getApplicationInfo().uid) == TrafficStats.UNSUPPORTED ?
                        0 : (TrafficStats.getTotalRxBytes() / 1024);//转为KB
}

没事了，，，，模拟器无效。TrafficStats.getUidRxBytes(MainActivity.this.getApplicationInfo().uid) 这个值为-1，代表不支持