卡利微：通過視圖模型

Question

之間對象我正在開發使用卡利微2.0.0-α-2

我在用的ViewModels之間的導航麻煩，傳遞對象的簡單的CRUD應用程序（在Windows 8.1存儲應用程序）。

我看了很多遍提出

安德斯·古斯塔夫鬆（How to pass parameter to navigated view model with WinRT Caliburn.Micro?）

的解決方案，我想它適應我的範圍。 但該對象是alwais null。

我需要將從listView中選擇的單個對象傳遞給我的crudPage。 crudPage由顯示FormView的userControl組成。 所以我想用傳遞對象的值初始化這個表單。

我認爲問題是隻有在創建ViewModel後才初始化「參數」，但我不知道如何解決這個問題。

有我的代碼，安德斯·古斯塔夫鬆的想法

TransporterListViewModel（從數據庫轉運的列表）

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); 
    } 

TransporterCrudViewModel（即cointains的用戶控件初始化頁面）

根據

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（userContol初始化）

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; } 

Answer 1

在構造函數中TransporterCrudViewModel類，你必須：

this.InitializeTransporterForm(Parameter); 

其中Parameter爲Transporter類型的屬性沒有初始化，你會調用該方法InitializeTransporterForm用null參數。然後，您將使用參數Transporter t的空值調用SetUpForm方法。我認爲你應該以某種方式初始化這個屬性。

然後，假設你在你的TransporterListViewModel類繼續與此：

transporterCrudPageViewModel.InitializeTransporterForm(args.Parameter as Transporter); 

的方法 InitializeTransporterForm

，你不這樣的設置傳遞的參數作爲屬性Parameter的價值：

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

除了這些筆記，你應該把斷點與IDE在該行

transporterCrudPageViewModel.InitializeTransporterForm(args.Parameter as Transporter); 

請確保NavigationEventArgs對象的屬性Parameter不爲空。