为什么 BLE 扫描在 Android 13 上对我不起作用？

Question

我正在使用 Jetpack Compose 构建一个扫描 BLE 设备的应用程序。这是一个可组合项，它在进入组合时简单地扫描 BLE 设备，并在退出时停止扫描。我已经获得BLUETOOTH_CONNECT和BLUETOOTH_SCAN的权限。问题是，当扫描开始时，什么也没有发生。程序没有崩溃，但我也找不到任何 BLE 设备。我注意到 logcat 中出现错误：“uid 1002 进行的错误调用。包“top.frankyang.gc”不属于 uid 1002。”，这与失败有关吗？我该如何解决这个问题或者我的代码有什么问题吗？我正在使用 Android 13，我的程序面向 Android 12。

// when this Composable enters composition, it's certain that we have the permission
@SuppressLint("MissingPermission")
@Composable
fun BleScanner(adapter: BluetoothAdapter) {
    val scanner = adapter.bluetoothLeScanner
    val devices = remember { mutableStateListOf<BluetoothDevice>() }
    val callback = remember {
        object : ScanCallback() {
            override fun onScanResult(callbackType: Int, result: ScanResult) {
                super.onScanResult(callbackType, result)
                Log.i(TAG, "onScanResult: new device found: ${result.device}")
                devices.add(result.device)
            }

            override fun onBatchScanResults(results: MutableList<ScanResult>) {
                super.onBatchScanResults(results)
                Log.i(TAG, "onBatchScanResults: new devices found: $results")
                results.mapTo(devices) { it.device }
            }

            override fun onScanFailed(errorCode: Int) {
                Log.w(TAG, "onScanFailed: scan failure: errorCode=$errorCode")
            }
        }
    }

    for (device in devices) {
        Text(device.name)
    }
    if (devices.isEmpty()) {
        Text(stringResource(R.string.no_device))
    }

    DisposableEffect(scanner) {
        Log.i(TAG, "BleScanner: start scanning for BLE devices")
        scanner.startScan(callback)
        onDispose {
            Log.i(TAG, "BleScanner: scanning stopped or adapter changed")
            scanner.stopScan(callback)
        }
    }
}

2023-12-29 20:58:42.902 25173-25173 Bt                      top.frankyang.gc                     I  BleScanner: scanning stopped or adapter changed
2023-12-29 20:58:42.903 25173-25173 BluetoothAdapter        top.frankyang.gc                     D  isLeEnabled(): ON
2023-12-29 20:58:42.906 25173-25173 BluetoothAdapter        top.frankyang.gc                     D  isLeEnabled(): ON
2023-12-29 20:58:43.862 25173-25173 Bt                      top.frankyang.gc                     I  BleScanner: start scanning for BLE devices
2023-12-29 20:58:43.862 25173-25173 BluetoothAdapter        top.frankyang.gc                     D  isLeEnabled(): ON
2023-12-29 20:58:43.866 25173-4472  BluetoothLeScanner      top.frankyang.gc                     D  onScannerRegistered() - status=0 scannerId=8 mScannerId=0
2023-12-29 20:58:43.870  2489-4327  AppOps                  system_server                        E  Bad call made by uid 1002. Package "top.frankyang.gc" does not belong to uid 1002.

Answer 1

在 BLUETOOTH_SCAN 权限声明中添加 android:usesPermissionFlags="neverForLocation" ，如下所示

<uses-permission android:name="android.permission.BLUETOOTH_SCAN" android:usesPermissionFlags="neverForLocation" />

否则扫描器不会给出结果（或者您可以在Manifest.xml中声明位置权限并打开设备位置）。

这样做会给出扫描结果。

注意：

1. 文本需要用 Column Composable 包裹

2. device.name

   可能会导致NPE