Android 蓝牙导致NPE

我想使用我在清单中添加的蓝牙

<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
<uses-permission android:name="android.permission.BLUETOOTH" />

但是在这里

mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);

我有这个错误

va.lang.NullPointerException:尝试调用虚拟方法 'android.bluetooth.BluetoothSocket位于空对象引用上

---

您的

mmDevice

没有正确实例化，这就是您得到

NullPointerException

的原因。通过简单的空检查来防止这种情况：

如果（mmDevice！=null）

您是否在运行时请求权限？自Android M以来，您应该检查活动的权限：

或者，如果您知道设备

地址

，则可以使用

mblueothmanager.adapter.getRemoteDevice（“deviceAddress”）

---

方法。

什么是mmsocket？如果它是一个对象而不是像这样初始化，例如：Textview text；并引用id（如果存在）。

mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);

private void checkPermissions() {
    ArrayList<String> permissions = ArrayList();
    if (checkSelfPermission(applicationContext, ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED)
        permissions.add(ACCESS_FINE_LOCATION);
    if (checkSelfPermission(applicationContext, BLUETOOTH) != PackageManager.PERMISSION_GRANTED)
        permissions.add(BLUETOOTH);
    if (checkSelfPermission(applicationContext, BLUETOOTH_ADMIN) != PackageManager.PERMISSION_GRANTED)
        permissions.add(BLUETOOTH_ADMIN);
    if (permissions.isNotEmpty())
        requestPermissions(permissions.toTypedArray(), REQUEST_PERMISSIONS);
    else {
    startBluetoothService();
    }
}

BluetoothManager mBluetoothManager = (BluetoothManager)getSystemService(Context.BLUETOOTH_SERVICE);
BluetoothAdapter mBluetoothAdapter = mBluetoothManager.adapter;
//check if bluetooth is enabled 
if (mBluetoothAdapter.isEnabled){
    mBluetoothAdapter.startDiscovery(); 
    //make sure you register this receiver to properly receive callbacks
    mReceiver = new BroadcastReceiver() {
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        //Finding devices                 
        if (BluetoothDevice.ACTION_FOUND.equals(action)) {
            // Get the BluetoothDevice object from the Intent
            BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
            doThingsWithDevice();
    }
  }
}
};