如何通过编程方式向路由事件添加TypedEventHandler？

Question

如何通过编程方式向路由事件添加TypedEventHandler？

c#.netwindows-runtimewindows-phone-8.1windows-8.1

3

我正在编写一个扩展方法，但是其中有一部分出现了问题。

我的想法是：创建一个方法，该方法接受一个对象和事件名称，等待事件被触发，然后返回其事件参数。我将使用它来避免每次在代码中执行此类操作时手动创建委托等内容。

注意：代码位于针对Windows8.1和Windows Phone 8.1的PCL中，因此某些反射方法在此处不可用。

目前为止，我已经完成了以下工作：

/// <summary>
/// Waits for an event to be raised and returns its arguments
/// </summary>
/// <typeparam name="Targs">The type of the event args to return</typeparam>
/// <param name="target">The target object that will raise the event</param>
/// <param name="eventName">The name of the event to wait</param>
/// <param name="timeout">The time limit (in millisecond) to wait for the desired event to be raised</param>
public static async Task<Targs> WaitEventAsync<Targs>(this object target, String eventName, int timeout)
    where Targs : class
{
    // Arguments check
    if (target == null) throw new ArgumentNullException("The target object can't be null");
    if (eventName == null) throw new ArgumentNullException("The event name can't be null");
    if (timeout <= 0) throw new ArgumentOutOfRangeException("The timeout must be greater than 0");

    // Get the target event
    EventInfo eventInfo = target.GetType().GetRuntimeEvent(eventName);
    if (eventInfo == null) throw new ArgumentException(String.Format("The target object doesn't contain the {0} event", eventName));

    // Prepare the TaskCompletionSource, the return variable and the right handler
    TaskCompletionSource<Targs> tcs = new TaskCompletionSource<Targs>();

    Delegate handler;

    if (eventInfo.EventHandlerType.Equals(typeof(EventHandler<Targs>)))
    {
        handler = new EventHandler<Targs>((sender, args) =>
        {
            tcs.SetResult(args);
        });
    }
    else
    {
        // PROBLEM: when this line is executed, the AddEventHandler method crashes
        handler = new TypedEventHandler<object, Targs>((sender, args) => 
       { 
           tcs.SetResult(args); 
       });
    }

    // Add the handler and wait for the event
    eventInfo.AddEventHandler(target, handler);
    CancellationTokenSource cts = new CancellationTokenSource(timeout);
    try
    {
        // If the event was triggered before the timout expired, return its args
        return await tcs.Task.GetWatchedTask(cts);
    }
    catch (OperationCanceledException)
    {
        // If the timout expired, just return null
        return null;
    }
    finally
    {
        // Remove the handler from the target object
        eventInfo.RemoveEventHandler(target, handler);
    }
}

现在，标准事件一切正常，没有问题。但是当我使用“RoutedEvents”时，会出现异常。我最终尝试使用“TypedEventHandler”类，因为我没有找到其他方法来获取这些事件的正确委托（如所有指针事件）。但是，当我尝试添加处理程序时，会出现“InvalidOperationException”的异常。是否可能在WinRT上也为RoutedEvents创建运行时处理程序，还是不可能？感谢您的帮助！Sergio

- Sergio0694

1个回答

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- MrCSharp · Accepted Answer

你遇到了这个异常，因为WinRT不允许使用AddHandler方法添加事件处理程序。我所知道的唯一可以做到这一点的方法是使用这段代码：

    private void AddHandler(FrameworkElement element, object parameter, EventInfo eventInf)
    {
        var addMethod = eventInf.AddMethod;
        var removeMethod = eventInf.RemoveMethod;

        var addParameters = addMethod.GetParameters();
        var delegateType = addParameters[0].ParameterType;

        Action<object, object> handler = (s, e) => ExecuteCommand();
        var handlerInvoke = typeof(Action<object, object>).GetRuntimeMethod("Invoke", new[] { typeof(object), typeof(object) });

        var @delegate = handlerInvoke.CreateDelegate(delegateType, handler);

        Func<object, EventRegistrationToken> add = a => (EventRegistrationToken)addMethod.Invoke(element, new object[] { @delegate });
        Action<EventRegistrationToken> remove = t => removeMethod.Invoke(element, new object[] { t });

        WindowsRuntimeMarshal.AddEventHandler(add, remove, handler);
    }

要删除处理程序，请使用以下方法：

WindowsRuntimeMarshal.RemoveEventHandler(remove, handler);