以编程方式扫描蓝牙设备在安卓6+中找不到任何东西

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

if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION)
        != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(this,
            new String[]{Manifest.permission.ACCESS_COARSE_LOCATION},
            REQUEST_CODE_LOCATION_PERMISSION);
}

BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
if (bluetoothAdapter == null || !bluetoothAdapter.isEnabled()) {
    Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
    startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}

private final BroadcastReceiver scanReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (BluetoothAdapter.ACTION_DISCOVERY_STARTED.equals(action)) {
            // 扫描开始
        } else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
            // 扫描结束
        } else if (BluetoothDevice.ACTION_FOUND.equals(action)) {
            // 发现蓝牙设备
            BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
            // 处理设备信息
        } else if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
            // 蓝牙状态改变
            int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR);
            if (state == BluetoothAdapter.STATE_OFF) {
                // 蓝牙关闭
            } else if (state == BluetoothAdapter.STATE_ON) {
                // 蓝牙开启
            }
        }
    }
};

// 注册广播接收器
IntentFilter filter = new IntentFilter();
filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_STARTED);
filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
filter.addAction(BluetoothDevice.ACTION_FOUND);
filter.addAction(BluetoothAdapter.ACTION_STATE_CHANGED);
registerReceiver(scanReceiver, filter);

// 开始扫描
BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
bluetoothAdapter.startDiscovery();