Android蓝牙无法进入BroadcastReceiver的问题排查与解决

问题现象 #

按照Android官方蓝牙开发教程实现设备搜索功能时，日志仅能打印"1"，无法进入BroadcastReceiver（无"2"日志输出），调整接收器注册方式后问题依旧。

初始实现代码 #

public class ScanList extends AppCompatActivity {

BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
BroadcastReceiver mReceiver;
int REQUEST_ENABLE_BT = 1;
ArrayAdapter<String> mArrayAdapter;

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


    if (mBluetoothAdapter != null) {
        if (!mBluetoothAdapter.isEnabled()) {
            Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            if (ContextCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(
                        this,
                        new String[]{Manifest.permission.BLUETOOTH_CONNECT}, REQUEST_ENABLE_BT
                );
            }
            startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
        }
    }

    IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
    registerReceiver(receiver, filter);
    mBluetoothAdapter.startDiscovery();
    Log.i("devi", "1");   // can only print this line
}

// Create a BroadcastReceiver for ACTION_FOUND.
private BroadcastReceiver receiver = new BroadcastReceiver() {
    public void onReceive(Context context, Intent intent) {
        Log.i("devi", "2");
        String action = intent.getAction();

        if (BluetoothDevice.ACTION_FOUND.equals(action)) {
            // Discovery has found a device. Get the BluetoothDevice
            // object and its info from the Intent.
            BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
            if (ActivityCompat.checkSelfPermission(ScanList.this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(
                        ScanList.this,
                        new String[]{Manifest.permission.BLUETOOTH_CONNECT}, REQUEST_ENABLE_BT
                );
            }
            String deviceName = device.getName();
            String deviceHardwareAddress = device.getAddress(); // MAC address
            Log.i("devi", deviceName);
            Log.i("devi", deviceHardwareAddress);


            Intent reintent = new Intent(ScanList.this, MainActivity.class);
            Bundle extras = new Bundle();
            extras.putString("name",deviceName);
            extras.putString("address",deviceHardwareAddress);
            reintent.putExtras(extras);
            startActivity(reintent);
            finish();
        }
    }
};

@Override
protected void onDestroy() {
    super.onDestroy();
    unregisterReceiver(receiver);
}
}

补充调试情况 #

在mBluetoothAdapter.startDiscovery();和String deviceName = device.getName();前添加以下权限检查代码后，能够获取到设备，但功能不稳定：扫描未必能进入BroadcastReceiver，且进入时会崩溃，提示“Bluetooth keeps stopping”（Bluetooth为应用名称）。

补充的权限检查代码：

if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(
                MainActivity.this,
                new String[]{Manifest.permission.BLUETOOTH_CONNECT}, 1001
    );
}

最终解决方案 #

问题根源：部分蓝牙设备未设置名称，调用device.getName()会返回null，直接打印或传递null值会引发空指针异常，导致应用崩溃。

修复方式：添加空值判断，处理deviceName为null的情况，示例代码如下：

String deviceName = device.getName();
// 空值判断，避免空指针异常
if (deviceName == null) {
    deviceName = "未知设备";
}
String deviceHardwareAddress = device.getAddress(); // MAC address
Log.i("devi", deviceName);
Log.i("devi", deviceHardwareAddress);

额外优化建议：
初始BroadcastReceiver不触发的潜在原因是扫描启动时机过早，建议将mBluetoothAdapter.startDiscovery()移至蓝牙开启回调onActivityResult或权限申请回调onRequestPermissionsResult中，确保蓝牙就绪、权限获取完成后再启动扫描。

内容的提问来源于stack exchange，提问作者yolopoi