Question

我尝试实现android developer USB example code，我得到了NullPointerException

04-11 19：53：34.295：E / initial（11917）：java.lang.NullPointerException

我的设备是NEXUS 7

这是我的代码

    @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_host);

    textView = (TextView)findViewById(R.id.textView1);
    myThread = new Thread(this, "myThread Thread");
    myThread.start();       
}

@Override
public void run() {
    // TODO Auto-generated method stub
    initial();
}

private void initial(){
    try {
        manager = (UsbManager) getSystemService(Context.USB_SERVICE);
        HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
        Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();

        mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
        IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
        registerReceiver(mUsbReceiver, filter);
        manager.requestPermission(device, mPermissionIntent);//the error came out at this line

        while(deviceIterator.hasNext()){
            device = deviceIterator.next();
            Log.d("deviceIterator", device.toString()); 
            runOnUiThread(new Runnable() {

                @Override
                public void run() {
                    // TODO Auto-generated method stub
                    textView.setText(device.toString());
                }
            });
        }
    } catch (Exception e) {
        Log.e("initial", e.toString());
    }

}

private final BroadcastReceiver mUsbReceiver = new BroadcastReceiver() {

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO Auto-generated method stub
        try {
            String action = intent.getAction();
            if (ACTION_USB_PERMISSION.equals(action)) {
                synchronized (this) {
                    UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                    if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                        if(device != null){
                            //call method to set up device communication
                        }
                    }else {
                        Log.d(TAG, "permission denied for device " + device);
                    }
                }
            }
        } catch (Exception e) {
            Log.e("onReceive", e.toString());
        }
    }

};

我做错了什么？抱歉我的虚拟问题，这是我第一次使用USB功能

Android USB主机NullPointerException

0 个答案: