Question

我是MVVM的新手，刚刚开始我的第一个项目遵循MVVM模式。我尝试使用IDataErrorInfo接口验证ObservableCollection时遇到问题。我的ObservableCollection看起来像这样：

ObservableCollection<Magazine> magazineRepository;
    public ObservableCollection<Magazine> MagazineRepository
    {
        get { return magazineRepository; }
        set
        {
            if (value != null)
            {
                bladRepository = value;
                OnPropertyChanged("MagazineRepository");
            }
        }
    }

我的XAML是这样的：

<ListBox x:Name="listMagazineRepository"
                 Grid.ColumnSpan="2"
                 ItemsSource="{Binding}" 
                 DataContext="{Binding MagazineRepository}"
                 DisplayMemberPath="Navn" 
                 SelectedItem="{Binding Path=SelectedItem}"/>

        <TextBox x:Name="txtName" Grid.Row="1" Grid.Column="0"
                    Text="{Binding ElementName=listMagazineRepository, Path=SelectedItem.Navn, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
        <TextBox x:Name="txtPrice" Grid.Row="2" Grid.Column="0"
                    Text="{Binding ElementName=listMagazineRepository, Path=SelectedItem.Pris, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />

它只是一个包含对象的简单列表框，当您选择一个项目时，所选对象属性将显示在文本框中，然后绑定到列表框对象。

我的问题是，当我像这样设置代码时，我能够弄清楚如何验证我的数据的唯一方法是在域模型中，这实际上不是一个好习惯，我想验证在ViewModel到达之前。基本上我想验证MagazineRepository中的每个属性，在ViewModel中，你会怎么做呢？

PS：如果我的问题缺乏信息，我很想在这个主板（以及一般的编程板）上发帖，请告诉我，我将提供所需的详细信息。

非常感谢。

Answer 1

如果我理解正确，您想要验证Magazine对象。如果是这种情况，一种方法是将该类包装在viewmodel中，让我们称之为MagazineVM，它实现IDataErrorInfo并保持杂志对象的更新。然后，您将视图绑定到MagazineVM列表。作为一个非常简单的例子：

public class MagazineVM : IDataErrorInfo, INotifyPropertyChanged
{
   private Magazine _magazine;

   public int FirstMagazineProperty
   {
      get { return _magazine.FirstMagazineProperty; }
      set { _magazine.FirstMagazineProperty = value; RaisePropertyChanged("FirstMagazineProperty"); }
   }

   //INotifyPropertyChanged implementation

   //IDataErrorInfo implementation
}

Answer 2

首先，正如Dtex所说，你应该使用MagazineViewModel类而不是Magazine类。 E.G。

public class MagazineViewModel : INotifyPropertyChanged, IDataErrorInfo
{
  private string navn;
  private string pris;
  private string error;

  public string Navn
  {
    get { return navn; }
    set
    {
      if (navn != value)
      {
        navn = value;
        RaisePropertyChanged("Navn");
      }
    }
  }
  public string Pris
  {
    get { return pris; }
    set
    {
      if (pris != value)
      {
        pris = value;
        RaisePropertyChanged("Pris");
      }
    }
  }
  public string Error
  {
    get { return error; }
    set
    {
      if (error != value)
      {
        error = value;
        RaisePropertyChanged("Error");
      }
    }
  }

  public event PropertyChangedEventHandler PropertyChanged;

  public string this[string columnName]
  {
    get
    {
      var result = string.Empty;

      switch (columnName)
      {
        case "Pris":
          if (string.IsNullOrWhiteSpace(Pris))
          {
            result =  "Pris is required";
          }
          break;
        case "Navn":
          if (string.IsNullOrWhiteSpace(Navn))
          {
           result =  "Navn is required";
          }
          break;
      }

      return result;

    }
  }

  private void RaisePropertyChanged(string PropertyName)
  {
    var e = PropertyChanged;
    if (e != null)
    {
      e(this, new PropertyChangedEventArgs(PropertyName));
    }
  }

}

要注意的重要属性是“public string this [string columnName]”。 ColumnName将是您的绑定属性之一，您可以在此处进行验证。

接下来要考虑的是您的MainViewModel（您的DataContext）。 E.G。

public class MainViewModel : INotifyPropertyChanged
{
  //Use a readonly observable collection. If you need to reset it use the .Clear() method
  private readonly ObservableCollection<MagazineViewModel> magazines = new ObservableCollection<MagazineViewModel>();

  private MagazineViewModel selectedItem;

  //Keep the item being edited separate to the selected item
  private MagazineViewModel itemToEdit;

  public ObservableCollection<MagazineViewModel> Magazines { get { return magazines; } }
  public MagazineViewModel SelectedItem
  {
    get { return selectedItem; }
    set
    {
      if (selectedItem != value)
      {
        selectedItem = value;
        RaisePropertyChanged("SelectedItem");
        //When the selected item changes. Copy it to the ItemToEdit
        //This keeps the the copy you are editing separate meaning that invalid data isn't committed back to your original view model
        //You will have to copy the changes back to your original view model at some stage)
        ItemToEdit = Copy(SelectedItem);
      }
    }
  }
  public MagazineViewModel ItemToEdit
  {
    get { return itemToEdit; }
    set
    {
      if (itemToEdit != value)
      {
        itemToEdit = value;
        RaisePropertyChanged("ItemToEdit");
      }
    }
  }

  public event PropertyChangedEventHandler PropertyChanged;

  public MainViewModel()
  {
    //Ctor...
  }

  //Create a copy of a MagazineViewModel
  private MagazineViewModel Copy(MagazineViewModel ToCopy)
  {
    var vm = new MagazineViewModel();
    vm.Navn = ToCopy.Navn;
    vm.Pris = ToCopy.Pris;
    return vm;
  }

  private void RaisePropertyChanged(string PropertyName)
  {
    //...
  }
}

这里唯一缺少的是如何将更改复制回原始视图模型。您可以在所选项目更改之前（如果ItemToEdit有效）执行此操作，或者只有在ItemToEdit有效时才启用提交按钮。如果您可以允许原始视图模型进入无效状态，则无需担心复制。

最后是XAML

显示错误工具提示的隐式样式

<Style
  TargetType="{x:Type TextBox}">
  <Setter
    Property="ToolTip"
    Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}" />
</Style>

控件和绑定

<ListBox
  ItemsSource="{Binding Magazines}"
  DisplayMemberPath="Navn"
  SelectedItem="{Binding Path=SelectedItem, Mode=TwoWay}" />
<TextBox
  Margin="5"
  x:Name="txtName"
  Grid.Row="1"
  Grid.Column="0"
  Text="{Binding ItemToEdit.Navn, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
<TextBox
  Margin="5"
  x:Name="txtPrice"
  Grid.Row="2"
  Grid.Column="0"
  Text="{Binding ItemToEdit.Pris, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />

TextBoxes绑定到ItemToEdit。 ItemToEdit将是SelectedItem的同步副本。

使用MVVM Pattern在ViewModel中验证绑定的ObservableCollection

2 个答案: