迁移至MAUI的iOS应用如何获取蓝牙权限？

问题背景 #

将Xamarin.Forms应用迁移至MAUI后，iOS端创建CBCentralManager实例后状态始终为CBManagerState.Unknown，无法触发蓝牙权限请求弹窗，原Xamarin.Forms中的权限请求逻辑失效。原iOS项目已在info.plist中配置了以下权限字符串：

NSBluetoothPeripheralUsageDescription
NSBluetoothAlwaysUsageDescription
Privacy - Bluetooth Peripheral Usage Description
Privacy - Bluetooth Always Usage Description

原权限请求逻辑（更新后）：

public async Task<bool> RequestBluetoothPermission()
{
    //iOS 13.0 and below
    if (!UIDevice.CurrentDevice.CheckSystemVersion(13, 1))
    {
        return true;
    }

    //iOS 13.1 and above
    if (CBManager.Authorization == CBManagerAuthorization.NotDetermined)
    {
        TaskCompletionSource<CBCentralManagerState> tcs = new TaskCompletionSource<CBCentralManagerState>();
        Action<CBCentralManagerState> handleBluetoothStateChangedForFirstTime = delegate (CBCentralManagerState bluetoothState)
       {
           HandleBluetoothStateChanged(bluetoothState);
           tcs.TrySetResult(bluetoothState);
       };

        var simpleCBCentralManagerDelegate = new SimpleCBCentralManagerDelegate();
        simpleCBCentralManagerDelegate.StateChanged += handleBluetoothStateChangedForFirstTime;

        _cBCentralManager = new CBCentralManager(simpleCBCentralManagerDelegate, null, new CBCentralInitOptions() { ShowPowerAlert = false });
        var status = await tcs.Task;

        simpleCBCentralManagerDelegate.StateChanged -= handleBluetoothStateChangedForFirstTime;
        simpleCBCentralManagerDelegate.StateChanged += HandleBluetoothStateChanged;

        return status != CBCentralManagerState.Unauthorized;
    }

    // In any else case we can't ask again so we just return the current permission status
    return CBManager.Authorization == CBManagerAuthorization.AllowedAlways;
}

解决步骤 #

1. 修正info.plist权限配置 #

MAUI中iOS的权限配置需在Platforms/iOS/Info.plist中添加标准键值对，无需保留带Privacy -前缀的旧写法，同时确保权限描述内容不为空：

<key>NSBluetoothAlwaysUsageDescription</key>
<string>需要蓝牙权限连接并管理外设</string>
<key>NSBluetoothPeripheralUsageDescription</key>
<string>需要蓝牙权限扫描附近外设</string>

注：iOS 13及以上版本主要依赖NSBluetoothAlwaysUsageDescription，保留旧键是为了兼容更低版本系统。

2. 重构权限请求逻辑 #

MAUI中需确保CBCentralManager实例被正确持有，且状态回调能被可靠触发，修改后的代码如下：

private CBCentralManager? _centralManager;
private TaskCompletionSource<CBManagerAuthorization>? _authTaskSource;

public async Task<bool> RequestBluetoothPermission()
{
    // iOS 13.0及以下无需主动请求权限
    if (!UIDevice.CurrentDevice.CheckSystemVersion(13, 1))
    {
        return true;
    }

    var currentAuth = CBManager.Authorization;
    // 已授权或拒绝，直接返回当前状态
    if (currentAuth != CBManagerAuthorization.NotDetermined)
    {
        return currentAuth == CBManagerAuthorization.AllowedAlways;
    }

    _authTaskSource = new TaskCompletionSource<CBManagerAuthorization>();
    var authDelegate = new BluetoothAuthDelegate();
    authDelegate.OnAuthorizationUpdated += HandleAuthUpdate;

    // 初始化CBCentralManager，绑定主线程队列避免回调丢失
    _centralManager = new CBCentralManager(authDelegate, DispatchQueue.MainQueue, new CBCentralInitOptions
    {
        ShowPowerAlert = false
    });

    // 等待权限请求结果
    var finalAuth = await _authTaskSource.Task;
    authDelegate.OnAuthorizationUpdated -= HandleAuthUpdate;

    return finalAuth == CBManagerAuthorization.AllowedAlways;
}

private void HandleAuthUpdate(CBManagerAuthorization status)
{
    _authTaskSource?.TrySetResult(status);
}

// 自定义Delegate监听权限状态
private class BluetoothAuthDelegate : CBCentralManagerDelegate
{
    public event Action<CBManagerAuthorization>? OnAuthorizationUpdated;

    public override void UpdatedState(CBCentralManager central)
    {
        OnAuthorizationUpdated?.Invoke(CBManager.Authorization);
    }
}

3. 核心注意事项 #

• 持有CBCentralManager实例：必须在类级别声明变量（如_centralManager）持有实例，避免被垃圾回收导致回调不触发。
• 指定有效队列：初始化时绑定DispatchQueue.MainQueue或其他有效队列，防止因队列问题丢失状态回调。
• 监听UpdatedState方法：iOS蓝牙权限状态变化会通过该方法通知，需在此处获取最新授权状态。
• 避免重复请求：仅当CBManager.Authorization为NotDetermined时发起请求，否则直接返回当前状态。

内容的提问来源于stack exchange，提问作者o_w