未调用 Xamarin MessagingCenter 回调

Question

我正在使用 Xamarin MessagingCenter 实现设备方向检测器。我想做的是将消息从 Android 项目中的 MainActivity 发送到我的 .NET Standart 项目中的 Singleton class 实现。

如您所见，我在 MainActivity 中覆盖了 "OnConfigurationChanged(...)" 方法，当我将方向从横向切换为纵向时，所有断点都在我的 IF 语句中命中。问题是我最近收到了这些消息。我的 "OrientationHelper" 中的回调是较新调用的。

"OrientationHelper" 在第一页加载时实例化（对于那些会说我没有实例的人:)）

主要活动：

public override void OnConfigurationChanged(Android.Content.Res.Configuration newConfig)
{
    base.OnConfigurationChanged(newConfig);

    if (newConfig.Orientation == Android.Content.Res.Orientation.Landscape)
        MessagingCenter.Send(this, "OrientationContract"
            , new OrientationChangedEventArgs(Orientation.Landscape));

    else if (newConfig.Orientation == Android.Content.Res.Orientation.Portrait)
        MessagingCenter.Send(this, "OrientationContract"
            , new OrientationChangedEventArgs(Orientation.Portrait));
}

将从 MainActivity 接收消息的单例 class：

public class OrientationHelper
{
    private OrientationHelper()
        => MessagingCenter.Subscribe<OrientationChangedEventArgs>(this, "OrientationContract"
            , s => DeviceOrientation = s.Orientation);

    private static OrientationHelper s_instace;
    public static OrientationHelper Instance
    {
        get
        {
            if (s_instace == null)
                s_instace = new OrientationHelper();
            return s_instace;
        }
    }

    private Orientation _deviceOrientation;
    public Orientation DeviceOrientation
    {
        get => _deviceOrientation;
        private set
        {
            if (_deviceOrientation == value)
                return;
            _deviceOrientation = value;
        }
    }
}

OrientationChangedEventArgs:

public class OrientationChangedEventArgs : EventArgs
{
    public Orientation Orientation { get; private set; }

    public OrientationChangedEventArgs(Orientation orientation)
        => Orientation = orientation;
}

Answer 1

订阅和发送方法是这样定义的

Subscribe (object subscriber, string message, Action callback, TSender source = null)

Send (TSender sender, string message) Send (TSender sender, string message, TArgs args)

两个调用中的第一个 T 参数应与 class 发送消息的类型匹配

MessagingCenter.Send<MyType, OrientationChangedEventArgs>(this, "OrientationContract"
        , new OrientationChangedEventArgs(Orientation.Landscape));

MessagingCenter.Subscribe<MyType, OrientationChangedEventArgs>(this, "OrientationContract"
        , s => DeviceOrientation = s.Orientation);

未调用 Xamarin MessagingCenter 回调

Xamarin MessagingCenter callback not being called

.net

c#

android

xamarin

messagingcenter