Caliburn Micro：在 ViewModel 之间传递对象

我正在使用 Caliburn Micro 2.0.0-alpha2 开发一个简单的 Crud 应用程序（一个 Windows 8.1 商店应用程序）

我在视图模型之间导航、传递对象时遇到麻烦。

我多次阅读了提出的解决方案

安德斯·古斯塔夫森（如何使用 WinRT Caliburn.Micro 将参数传递给导航视图模型？ https://stackoverflow.com/questions/15251867/how-to-pass-parameter-to-navigated-view-model-with-winrt-caliburn-micro)

我尝试让它适应我的范围。 但该对象始终为空。

I need to pass a single object selected from a listView to my crudPage. The crudPage is composed by an userControl that shown the FormView. So i want to initialize this Form, with the values of the passed object.

我认为问题在于“参数”仅在创建 ViewModel 之后才初始化，但我不知道如何解决该问题。

这是我的代码，根据 Anders Gustafsson 的想法

TransporterListViewModel（数据库中的运输商列表）

public class TransporterListViewModel : ViewModelBase
{
    public string Title { get; set; }
    public TransporterListViewModel(INavigationService navigationService)
        : base(navigationService)
    {
        LoadData();
    }

    public async void LoadData() {

        _transporters = await TransporterService.GetAll();
    }

    private BindableCollection<Transporter> _transporters;

    public BindableCollection<Transporter> Transporters
    {
        get
        {
            return this._transporters;
        }
        set
        {
            this._transporters = value;
            NotifyOfPropertyChange(() => this.Transporters);
        }
    }

    private Transporter _selectedItem;
    public Transporter SelectedItem
    {
        get 
        {

            return _selectedItem;
        }

        set
        {
            _selectedItem = value;
            NotifyOfPropertyChange(() => this.SelectedItem);

            navigationService.Navigated += NavigationServiceOnNavigated;
            navigationService.NavigateToViewModel<TransporterCrudPageViewModel>(_selectedItem;);
            navigationService.Navigated -= NavigationServiceOnNavigated;
        }
    }

    private static void NavigationServiceOnNavigated(object sender, NavigationEventArgs args)
    {
        FrameworkElement view;
        TransporterCrudPageViewModel transporterCrudPageViewModel;
        if ((view = args.Content as FrameworkElement) == null ||
            (transporterCrudPageViewModel = view.DataContext as TransporterCrudPageViewModel) == null) return;

        transporterCrudPageViewModel.InitializeTransporterForm(args.Parameter as Transporter);
    } 

Transporter Crud ViewModel（包含要初始化的用户控件的页面）

public class TransporterCrudPageViewModel : ViewModelBase
{
    public string Title { get; set; }

    public Transporter Parameter { get; set; }
    public TransporterFormViewModel TransporterFormVM { get; set; }

    public async void InitializeTransporterForm(Transporter enumerable)
    {
        TransporterFormVM = new TransporterFormViewModel(navigationService, enumerable);
        await SetUpForm(enumerable);
    }

    public async Task SetUpForm(Transporter t){
        TransporterFormVM.trName = t.trName;
        TransporterFormVM.trUrl = t.trUrl;

    }
    public TransporterCrudPageViewModel(INavigationService navigationService)
        : base(navigationService)
    {
        Title = "TransporterCrud Page";
        //this.navigationService = navigationService;

        this.InitializeTransporterForm(Parameter);

    }

TransporterFormViewModel（要初始化的 userContol）

    public class TransporterFormViewModel :ViewModelBase
{


    public string Title { get; set; }

    public Transporter Transporter { get; set; }

    public TransporterFormViewModel(INavigationService navigationService,Transporter trans)
        : base(navigationService)
    {
        Transporter = trans;
    }



    private string _trName;
    public string trName 
    {
        get
        {
            return _trName;
        }
        set
        {
            _trName = value;
            NotifyOfPropertyChange(() => trName);
        }
    }


    public string trCode { get; set; }
    public string trUrl { get; set; }

    public int trId { get; set; }

在构造函数中TransporterCrudViewModel你有的课程：

this.InitializeTransporterForm(Parameter);

where Parameter是类型的属性Transporter未初始化，您将调用该方法InitializeTransporterForm with a null范围。然后你会打电话SetUpForm参数为空值的方法Transporter t。我认为你应该以某种方式初始化这个属性。

然后，假设您继续您的TransporterListViewModel与此类：

transporterCrudPageViewModel.InitializeTransporterForm(args.Parameter as Transporter);

在方法中InitializeTransporterForm，您没有将传递的参数设置为属性的值Parameter像这样的东西：

public async void InitializeTransporterForm(Transporter enumerable)
{
     TransporterFormVM = new TransporterFormViewModel(navigationService, enumerable);
     this.Parameter = enumerable; //setting the Parameter property..
     await SetUpForm(enumerable);
}

除了这些注释之外，您还应该在您的 IDE 中放置一个断点

transporterCrudPageViewModel.InitializeTransporterForm(args.Parameter as Transporter);

确保该房产Parameter of the NavigationEventArgs对象不为空。