为什么广播接收器在 Jetpack Compose 中被调用两次？

Question

我在 Jetpack Compose 应用程序中遇到一个问题，当蓝牙关闭时，

ACTION_STATE_CHANGED

广播接收器似乎被调用两次。我有一个可组合函数BluetoothStateListener，它注册一个广播接收器来侦听蓝牙状态的变化。但是，当我关闭蓝牙时，广播接收器的 onReceive 函数被调用两次，导致意外行为。

class MainActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            var isBluetoothEnable by remember { mutableStateOf(false) }
            ScreenOne(isBluetoothEnable) { isBluetoothEnable = it }
        }
    }
}

@Composable
fun ScreenOne(isBluetoothEnable: Boolean, onBluetoothChange: (Boolean) -> Unit) {
    Text(text = "Hello world isBluetoothEnable $isBluetoothEnable")

    BluetoothStateListener {
        onBluetoothChange(it)
        Log.i("BluetoothStateListener", "isBluetoothEnable $it")
    }
}

@Composable
fun BluetoothStateListener(
    context: Context = LocalContext.current,
    isBluetoothEnable: (Boolean) -> Unit
) {
    DisposableEffect(Unit) {
        val receiver = object : BroadcastReceiver() {
            override fun onReceive(context: Context?, intent: Intent?) {
                if (intent?.action == BluetoothAdapter.ACTION_STATE_CHANGED) {
                    val state =
                        intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR)
                    isBluetoothEnable(state == BluetoothAdapter.STATE_ON)
                }
            }
        }
        val filter = IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED)
        context.registerReceiver(receiver, filter)
        onDispose {
            context.unregisterReceiver(receiver)
        }
    }
}

在打印日志中我可以看到日志函数正在打印值

2024-02-29 22:44:16.938 15425-15425 BluetoothStateListener  com.example.simplecomposenavigation  I  isBluetoothEnable false
2024-02-29 22:44:17.215 15425-15425 BluetoothStateListener  com.example.simplecomposenavigation  I  isBluetoothEnable true

Answer 1

您正在通过比较其状态来检查蓝牙是否已启用：

isBluetoothEnable(state == BluetoothAdapter.STATE_ON)

，而有多种状态：

public static final int STATE_OFF = 10;
public static final int STATE_ON = 12;
public static final int STATE_TURNING_OFF = 13;
public static final int STATE_TURNING_ON = 11;

如果您记录当前状态，您将得到类似以下内容：

 state = 11
 isBluetoothEnable false
 state = 12
 isBluetoothEnable true
 state = 13
 isBluetoothEnable false
 state = 10
 isBluetoothEnable false

这意味着您应该只检查 ON 和 OFF 状态，如下所示：

when (state) {
    BluetoothAdapter.STATE_OFF -> isBluetoothEnable(false)
    BluetoothAdapter.STATE_ON -> isBluetoothEnable(true)
    else -> {}
}