Android 蓝牙状态监听

在Android系统中，当蓝牙的状态发生改变之后，系统会自动发送广播BluetoothAdapter#ACTION_STATE_CHANGED。我们只需要注册一个BroadcastReceiver监听系统广播就可以实现对蓝牙状态的监听。

权限说明

• Android 11 (API 30) 及以下：需要 android.permission.BLUETOOTH。
• Android 12 (API 31) 及以上：如果需要通过 BluetoothAdapter 获取状态，通常需要 android.permission.BLUETOOTH_CONNECT 权限。

ACTION_STATE_CHANGED 的 Intent 中包含两个重要的 Extra：

• BluetoothAdapter.EXTRA_STATE: 当前的新状态。
• BluetoothAdapter.EXTRA_PREVIOUS_STATE: 变化前的旧状态。

状态常量对照表

常量 (Int)	说明
BluetoothAdapter.STATE_OFF (10)	蓝牙已关闭
BluetoothAdapter.STATE_TURNING_ON (11)	蓝牙正在打开
BluetoothAdapter.STATE_ON (12)	蓝牙已打开
BluetoothAdapter.STATE_TURNING_OFF (13)	蓝牙正在关闭

代码

import android.bluetooth.BluetoothAdapter  
import android.content.BroadcastReceiver  
import android.content.Context  
import android.content.Intent  
import android.content.IntentFilter  
import androidx.compose.runtime.Composable  
import androidx.compose.runtime.DisposableEffect  
import androidx.compose.runtime.Stable  
import androidx.compose.ui.platform.LocalContext  
import androidx.core.content.ContextCompat  
  
class BluetoothBroadcastReceiver(  
    private var bluetoothStateChangeListener: BluetoothStateChangeListener? = null,  
) : BroadcastReceiver() {  
  
    override fun onReceive(context: Context?, intent: Intent?) {  
        val extra =  
            intent?.takeIf { it.action == BluetoothAdapter.ACTION_STATE_CHANGED }?.extras ?: return  
        val state = extra.getInt(BluetoothAdapter.EXTRA_STATE)  
        val oldState = extra.getInt(BluetoothAdapter.EXTRA_PREVIOUS_STATE)  
        bluetoothStateChangeListener?.onChange(oldState, state)  
        if (intent?.action == BluetoothAdapter.ACTION_STATE_CHANGED) {
            val state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR)
            val oldState = intent.getIntExtra(BluetoothAdapter.EXTRA_PREVIOUS_STATE, BluetoothAdapter.ERROR)
            bluetoothStateChangeListener?.onChange(oldState, state)
        }
    }  
}  
  
@Stable  
fun interface BluetoothStateChangeListener {  
    fun onChange(oldState: Int, newState: Int)  
}  
 
@Composable  
fun BluetoothStateChange(onChangeListener: BluetoothStateChangeListener) {  
    val context = LocalContext.current  
    DisposableEffect(onChangeListener) {  
        val intentFilter = IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED)  
        val receiver = BluetoothBroadcastReceiver(onChangeListener)  
        ContextCompat.registerReceiver(  
            context, receiver, intentFilter, ContextCompat.RECEIVER_NOT_EXPORTED  
        )  
        onDispose {  
            context.unregisterReceiver(receiver)  
        }  
    }
}