Question

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" />

接下来我这样做了：

String uid = "0000111f-0000-1000-8000-00805f9b34fb";
    UUID uuid = UUID.fromString(uid.toUpperCase()); //Standard SerialPortService ID
    mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);
    mmSocket.connect();
    mmOutputStream = mmSocket.getOutputStream();
    mmInputStream = mmSocket.getInputStream();

但是在这里；

mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);

我遇到此错误

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

Answer 1

您的Ctrl+Shift+R实例化不正确，这就是为什么您获得<ion-app> <ion-header> <ion-toolbar> <ion-title>Footer</ion-title> </ion-toolbar> </ion-header> <ion-content > <ion-router-outlet > </ion-router-outlet> </ion-content> <ion-footer> <ion-toolbar> <ion-title>Footer</ion-title> </ion-toolbar> </ion-footer> </ion-app>的原因。可以通过简单的nullcheck来防止这种情况：mmDevice。

您是否在运行时请求权限？从Android M开始，您应该从“活动”中检查权限：

NullPointerException

确保正确实例化BluetoothDevice对象。为此，您应该使用BluetoothManager扫描设备：

if(mmDevice!=null)

或者，如果您知道设备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(); } }，则可以使用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(); } } } }; 方法。

蓝牙导致NPE

1 个答案: