使用Pending Intent的BLE Scanner无法获取ScanResults问题

问题描述 #

使用PendingIntent调用startScan进行BLE扫描时，广播接收器能被触发，但收到的Intent中没有任何额外数据（无扫描结果），该代码在旧版Android系统中可正常运行。

现有代码 #

扫描器代码 #

fun ComponentActivity.startScanner() {
    if (!checkForPermission(
            if (Build.VERSION.SDK_INT < Build.VERSION_CODES.S){
                Manifest.permission.ACCESS_COARSE_LOCATION
            }
            else {
                Manifest.permission.BLUETOOTH_SCAN
            }
    )){
        return
    }

    with(logViewModel) {
        if (!haveBtPermissions) {
            haveBtPermissions = true
            clear()
        }
    }

//    bluetoothAdapter.bluetoothLeScanner.startScan(filters, settings, scanCallback)
    bluetoothAdapter.bluetoothLeScanner.startScan(filters, settings, pendingIntent)
    Log.i(TAG, "Scanner started")
}

private val filters get() = mutableListOf<ScanFilter>().apply {
    val filterShortServiceUUID = ScanFilter.Builder()
        .setServiceUuid(ParcelUuid.fromString ("0000${"180D"}-0000-1000-8000-00805F9B34FB"))
        .build()
    add(filterShortServiceUUID)
}

private val settings get() = ScanSettings.Builder().setScanMode(
    ScanSettings.SCAN_MODE_BALANCED
).build()

private val ComponentActivity.bluetoothAdapter get() = (applicationContext
    .getSystemService(ComponentActivity.BLUETOOTH_SERVICE) as BluetoothManager).adapter

private val ComponentActivity.pendingIntent get() =
    applicationContext.let {appContext ->
        val intent = Intent(appContext, DeviceBroadcastReceiver::class.java)
//            .setAction("com.solvek.bletrigger.ACTION_FOUND")

        PendingIntent.getBroadcast(
            appContext, 0, intent,
            PendingIntent.FLAG_UPDATE_CURRENT or FLAG_IMMUTABLE
        )!!
    }

private fun ComponentActivity.checkForPermission(permission: String): Boolean {
    if (ActivityCompat.checkSelfPermission(
            this,
            permission
        ) == PackageManager.PERMISSION_GRANTED
    ) {
        return true
    }

    with(logViewModel) {
        append("Please grant permissions and restart app!")
        haveBtPermissions = false
    }

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S){
        registerForActivityResult(ActivityResultContracts.RequestMultiplePermissions()){
            startScanner()
        }.launch(arrayOf(
            Manifest.permission.BLUETOOTH_SCAN,
            Manifest.permission.BLUETOOTH_CONNECT
        ))
    }

    return false
}

接收器代码 #

class DeviceBroadcastReceiver: BroadcastReceiver() {
    override fun onReceive(context: Context?, intent: Intent?) {
        Log.i(TAG, "===== A new message received")
        if (context == null){
            Log.e(TAG, "Context is null")
            return
        }

        if (intent == null){
            Log.e(TAG, "Intent is null")
            return
        }

        val bleCallbackType: Int = intent.getIntExtra(BluetoothLeScanner.EXTRA_CALLBACK_TYPE, -1)
        if (bleCallbackType == -1){
            Log.w(TAG, "Callback type not specified")
            return
        }
        Log.i(TAG, "Received callback type $bleCallbackType")
    }
}

Manifest配置 #

<uses-permission
        android:name="android.permission.BLUETOOTH"
        android:maxSdkVersion="30" />
<uses-permission
        android:name="android.permission.BLUETOOTH_ADMIN"
        android:maxSdkVersion="30" />
<uses-permission
        android:name="android.permission.ACCESS_FINE_LOCATION"
        android:maxSdkVersion="30" />
<uses-permission
        android:name="android.permission.ACCESS_BACKGROUND_LOCATION"
        android:maxSdkVersion="30" />
<uses-permission
        android:name="android.permission.ACCESS_COARSE_LOCATION"
        android:maxSdkVersion="30" />

<!-- Request Bluetooth permissions for devices on API 31,32. -->
<uses-permission
        android:name="android.permission.BLUETOOTH_SCAN"
        tools:targetApi="s" />
<!-- Needed only if your app communicates with already-paired Bluetooth
             devices. -->
<uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
<!-- Since Bluetooth is a basic requirement for our app -->
<uses-feature
        android:name="android.hardware.bluetooth"
        android:required="true" />

<application
...

    <receiver android:name=".DeviceBroadcastReceiver"
        android:exported="false">
<!--            <intent-filter>-->
<!--                <action android:name="com.solvek.bletrigger.ACTION_FOUND" />-->
<!--            </intent-filter>-->
    </receiver>

解决要点及修改方案 #

1. 修正PendingIntent的Mutable标记 #

Android 12+（API 31+）中，FLAG_IMMUTABLE会阻止系统向Intent添加扫描结果数据，需改用FLAG_MUTABLE：

private val ComponentActivity.pendingIntent get() =
    applicationContext.let { appContext ->
        val intent = Intent(appContext, DeviceBroadcastReceiver::class.java)
            .setAction("com.solvek.bletrigger.ACTION_FOUND") // 添加唯一Action

        PendingIntent.getBroadcast(
            appContext, 0, intent,
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
                PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_MUTABLE
            } else {
                PendingIntent.FLAG_UPDATE_CURRENT
            }
        )!!
    }

2. 为ScanSettings指定回调类型 #

必须明确设置回调类型，否则系统不会传递扫描结果：

private val settings get() = ScanSettings.Builder()
    .setScanMode(ScanSettings.SCAN_MODE_BALANCED)
    .setCallbackType(ScanSettings.CALLBACK_TYPE_ALL_MATCHES) // 匹配所有结果
    .build()

3. 完善Manifest配置 #

给广播接收器添加IntentFilter匹配指定Action：

<receiver android:name=".DeviceBroadcastReceiver"
    android:exported="false">
    <intent-filter>
        <action android:name="com.solvek.bletrigger.ACTION_FOUND" />
    </intent-filter>
</receiver>

如果不需要位置权限辅助扫描，给BLUETOOTH_SCAN权限添加标记：

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

4. 在接收器中获取扫描结果 #

补充代码提取扫描结果：

override fun onReceive(context: Context?, intent: Intent?) {
    Log.i(TAG, "===== 收到新消息")
    if (context == null || intent == null) {
        Log.e(TAG, "Context或Intent为空")
        return
    }

    val bleCallbackType = intent.getIntExtra(BluetoothLeScanner.EXTRA_CALLBACK_TYPE, -1)
    if (bleCallbackType == -1) {
        Log.w(TAG, "未指定回调类型")
        return
    }
    Log.i(TAG, "收到回调类型 $bleCallbackType")

    // 获取扫描结果列表
    val scanResults = intent.getParcelableArrayListExtra<ScanResult>(BluetoothLeScanner.EXTRA_LIST_SCAN_RESULT)
    scanResults?.forEach { result ->
        Log.i(TAG, "发现设备: 名称=${result.device.name ?: "未知"}, MAC=${result.device.address}, RSSI=${result.rssi}")
    }
}

内容的提问来源于stack exchange，提问作者Solvek