Question

我正试图在iOS中使用mvvmcross实现模态确认弹出窗口，遵循this question中的Stuart大纲。尝试将InteractionRequest绑定到事件处理程序时，我收到以下异常：

Problem seen during binding execution for to ConfirmationInteraction - problem
TargetInvocationException: Exception has been thrown by the target of an invocation.

内部例外是：

ArgumentNullException: missing source event info in MvxWeakEventSubscription
Parameter name: sourceEventInfo
at Cirrious.CrossCore.WeakSubscription.MvxWeakEventSubscription`2[System.Object,System.EventArgs]..ctor (System.Object source, System.Reflection.EventInfo sourceEventInfo, System.EventHandler`1 targetEventHandler) [0x00000] in <filename unknown>:0 
at Cirrious.CrossCore.WeakSubscription.MvxGeneralEventSubscription..ctor (System.Object source, System.Reflection.EventInfo eventInfo, System.EventHandler`1 eventHandler) [0x00000] in <filename unknown>:0 
at Cirrious.CrossCore.WeakSubscription.MvxWeakSubscriptionExtensionMethods.WeakSubscribe (System.Reflection.EventInfo eventInfo, System.Object source, System.EventHandler`1 eventHandler) [0x00000] in <filename unknown>:0

大多数管道与上面引用的堆栈溢出问题相同，但为了完整性，我将在此处发布：

public class InteractionRequestedEventArgs : EventArgs
{
    public Action Callback 
    { 
        get; 
        private set; 
    }

    public object Context 
    { 
        get; 
        private set; 
    }

    public InteractionRequestedEventArgs(object context, Action callback)
    {
        Context = context;
        Callback = callback;
    }
}

InteractionRequest：

public class InteractionRequest<T> : IInteractionRequest
{
    public event EventHandler<InteractionRequestedEventArgs> Raised;

    public void Raise(T context, Action<T> callback)
    {
        var handler = this.Raised;
        if (handler != null)
        {
            handler(
                this, 
                new InteractionRequestedEventArgs(
                context, 
                () => callback(context)));
        }
    }
}

确认类：

public class Confirmation
{
    public string Message { get; private set; }
    public bool Confirmed { get; set; }
    public Confirmation(string message)
    {
        Message = message;
    }
}

在视图模型中，我们将请求设置为：

private InteractionRequest<Confirmation> _confirmCancelInteractionRequest = new InteractionRequest<Confirmation>();
    public IInteractionRequest ConfirmCancelInteractionRequest
    {
        get
        {
            return _confirmCancelInteractionRequest;
        }
    }

在视图中我们设置了事件订阅：

    private MvxGeneralEventSubscription _confirmationSubscription;
    private IInteractionRequest _confirmationInteraction;
    public IInteractionRequest ConfirmationInteraction
    {
        get { 
            return _confirmationInteraction; 
        }
        set
        {
            if (_confirmationInteraction == value)
                return;
            if (_confirmationSubscription != null)
                _confirmationSubscription.Dispose();
            _confirmationInteraction = value;
            if (_confirmationInteraction != null)
                _confirmationSubscription = _confirmationInteraction
                    .GetType ()
                    .GetEvent ("Raise")
                    .WeakSubscribe(_confirmationInteraction, DoConfirmation);

        }
    }

视图中的事件处理程序如下所示：

private void DoConfirmation(object s, EventArgs args)
    {
        var iArgs = (InteractionRequestedEventArgs)args;
        var confirmation = (Confirmation)iArgs.Context;

        var alert = new UIAlertView(); 
        alert.Title = "Bazinga"; 
        alert.Message = confirmation.Message; 

        alert.AddButton("Yes"); 
        alert.AddButton("No"); 

        alert.Clicked += (sender, e) => { 
            var alertView = sender as UIAlertView; 
                            // do something with the event
            iArgs.Callback();
        }; 
    }

最后是绑定，它位于视图的构造函数内部。视图是MT对话框元素，因此是DelayBind（）：

this.DelayBind(() =>
        {
            var set = this.CreateBindingSet<CustomerElement, CustomerViewModel>();
            ...
            set.Bind().For(my => my.ConfirmationInteraction).To(customer => customer.ConfirmCancelInteractionRequest);
            set.Apply();
        });
    }

Answer 1

带有堆栈的空引用异常

at Cirrious.CrossCore.WeakSubscription.MvxWeakEventSubscription`2[System.Object,System.EventArgs]..ctor (System.Object source, System.Reflection.EventInfo sourceEventInfo, System.EventHandler`1 targetEventHandler) [0x00000] in <filename unknown>:0 
at Cirrious.CrossCore.WeakSubscription.MvxGeneralEventSubscription..ctor (System.Object source, System.Reflection.EventInfo eventInfo, System.EventHandler`1 eventHandler) [0x00000] in <filename unknown>:0 
at Cirrious.CrossCore.WeakSubscription.MvxWeakSubscriptionExtensionMethods.WeakSubscribe (System.Reflection.EventInfo eventInfo, System.Object source, System.EventHandler`1 eventHandler) [0x00000] in <filename unknown>:0

只有在_confirmationInteraction.GetType ().GetEvent ("Raise")返回null

时才会出现

所以...我认为问题可能是你的事件被称为Raised

如果有帮助：

MvvmCross的3.0.13版本包括了一些用于交互的初始帮助者 - 例如见https://github.com/MvvmCross/MvvmCross/blob/v3/Cirrious/Cirrious.MvvmCross/ViewModels/MvxInteraction.cs - 我希望并期望在即将发布的版本中我们将以此为基础
简单的“消息框”互动@BrianChance提供了这个fab插件 - https://github.com/brianchance/MvvmCross-UserInteraction

MvvmCross绑定到InteractionRequest

1 个答案: