Question

这是我的ViewModel中的代码

public ICommand GoToCartCommand{
        get{ 
            return new MvxCommand (() => {                  
                var cartViewModel = Mvx.Resolve<CartViewModel>();
                if (cartViewModel != null)
                {
                    cartViewModel.cartlist.Add(new CartItemViewModel() { Name = Name, ID = ID, UnitPrice = double.Parse(Price), Quantity = 1, Description = Description, Image = Image });
                }
                cartListCount = cartViewModel.cartlist.Count;
                var messanger = Mvx.Resolve<IMvxMessenger>();
                var message = new MyMessage(this,"Product has been added",cartListCount);
                messanger.Publish(message);
            });
        }
    }


public class MyMessage : MvxMessage
{
    public int CartList_Count{ get; set;}   
    public string Message{ get; set;}

    public MyMessage(object sender,string _message,int _cartlist_count) : base(sender) { 
        this.Message = _message;
        this.CartList_Count = _cartlist_count;
    }
}

这是我的视图中的代码：

  var messenger = Mvx.Resolve<IMvxMessenger>();
_token = messenger.Subscribe<MyMessage>(OnInputIsNeeded,MvxReference.Strong);


private void OnInputIsNeeded(MyMessage _Message)
{
        Toast.MakeText (this.Activity,_Message.Message, ToastLength.Short).Show();
}

我的问题是，当我转到下一个视图OnInputisNeeded后回到此视图时，该方法被调用两次。当从这个视图返回时，当我再次访问此视图并单击按钮时，我得到NullReferenceException。

解决方案是什么？

这是什么意思： 没有注册MvxSubscriberChangeMessage类型的消息

如何注册MvxSubscriberChangeMessage？

MvvmCross Messenger中的NullReferenceException

0 个答案: