我正在尝试在 iOS 中使用 mvvmcross 实现模式确认弹出窗口，遵循 Stuart 在这个问题中的大纲。尝试将 InteractionRequest 绑定到事件处理程序时出现以下异常：
Problem seen during binding execution for to ConfirmationInteraction - problem
TargetInvocationException: Exception has been thrown by the target of an invocation.
内部异常是：
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
大多数管道与上面提到的堆栈溢出问题相同，但为了完整起见，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;
}
}
交互请求：
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，我们这样设置请求：
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中。该视图是一个 MT 对话元素，因此是 DelayBind()：
this.DelayBind(() =>
{
var set = this.CreateBindingSet<CustomerElement, CustomerViewModel>();
...
set.Bind().For(my => my.ConfirmationInteraction).To(customer => customer.ConfirmCancelInteractionRequest);
set.Apply();
});
}