打开所选ViewModel的视图

Question

我正在努力寻找正确的方法来做这件事。我有一个包含可观察到的MyViewModel集合的MyCollectionViewModel。我将这个绑定到一个视图MyCollectionView，并选择一个项目，绑定回MyCollectionViewModel中一个名为OpenMyViewCommand的命令。到目前为止一切顺利：

    private MvxCommand<MyViewModel> _openMyViewCommand;
    public ICommand OpenMyViewCommand
    {
        get {
            _openMyViewCommand= _openMyViewCommand?? new MvxCommand<MyViewModel>(OpenMyView);
            return _openSubViewCommand;
        }
    }

现在，当我触摸列表视图中的一项时，它将触发命令并调用方法OpenMyView，将所选的MyViewModel传递给该方法。现在的问题是，无论我如何尝试，似乎都可以让ShowViewModel显示所选模型的视图。我尝试过各种方法，但凭直觉，我希望像这样简单的东西能起作用：

    private void OpenMyView(MyViewModel item) {
                ShowViewModel<MyViewModel > (item);
    }

但是，当然不是这样的。我得到的错误是这样的：

013-06-10 10:46:05.849 MyAppIPhoneUI[51198:c07] mvx: Warning:   5.83 Problem creating viewModel of type MyViewModel - problem MvxException: Failed to resolve parameter for parameter model of type MyModel when creating MyApp.Core.MyViewModel
at Cirrious.CrossCore.IoC.MvxSimpleIoCContainer.GetIoCParameterValues (System.Type type, System.Reflection.ConstructorInfo firstConstructor) [0x00042] in /MvvmCross-3/CrossCore/Cirrious.CrossCore/IoC/MvxSimpleIoCContainer.cs:377 
at Cirrious.CrossCore.IoC.MvxSimpleIoCContainer.IoCConstruct (System.Type type) [0x00030] in /MvvmCross-3/CrossCore/Cirrious.CrossCore/IoC/MvxSimpleIoCContainer.cs:266 
at Cirrious.CrossCore.Mvx.IocConstruct (System.Type t) [0x00006] in /MvvmCross-3/CrossCore/Cirrious.CrossCore/Mvx.cs:115 
at Cirrious.MvvmCross.ViewModels.MvxDefaultViewModelLocator.TryLoad (System.Type viewModelType, IMvxBundle parameterValues, IMvxBundle savedState, IMvxViewModel& viewModel) [0x00004] in /MvvmCross-3/Cirrious/Cirrious.MvvmCross/ViewModels/MvxDefaultViewModelLocator.cs:27 

013-06-10 10:24:11.330 MyAppIPhoneUI[50878:c07] mvx: Warning:   6.87 Exception masked MvxException: Failed to load ViewModel for type MyApp.Core.MyViewModel from locator MvxDefaultViewModelLocator
  at Cirrious.MvvmCross.ViewModels.MvxViewModelLoader.LoadViewModel (Cirrious.MvvmCross.ViewModels.MvxViewModelRequest request, IMvxBundle savedState, IMvxViewModelLocator viewModelLocator) [0x00023] in /MvxViewModelLoader.cs:46 

知道这是怎么回事吗？我有一个继承自MvxViewController的MyView类，但它没有加载。

Answer 1

导航是通过像Android Intents和WindowsPhone Uris这样的东西来完成的-所以它必须通过可序列化的类型来完成-参见：

• Custom types in Navigation parameters in v3
• MvvmCross: How to pass paramters to view models with v3?
• http://slodge.blogspot.co.uk/2013/03/v3-new-viewmodel-lifecycle.html

尝试将您的代码更改为类似以下内容：

  ShowViewModel<MyViewModel>(new { id = item.Id });

使用如下的接收MyViewModel：

  public void Init(int id)
  {
     MyItem = myItemLookupService.Lookup(id);      
  }

此外，请记住，你对你的应用程序的生命周期几乎没有控制-它可能在任何时候被‘墓碑’。因此，不要期望仅仅因为MyViewModel接收到一个导航请求，该请求的项就会一直在内存中-您可能需要重新创建或获取它。