Question

我有一个主控件（MainWindow.xaml）和一个用户控件（ItemView.xaml）。 MainWindow包含所有ItemView-s的ItemsControl和一个添加项目的简单按钮。所有逻辑（应该是？）在两个相应的视图模型（MainWindowViewModel和ItemViewModel）中。下面是我的代码（尽可能简短），但我有两个问题：

添加新项目时，它会正确显示但引发异常（无法创建默认转换器以在类型'WpfApplication1.ItemView'和'WpfApplication1.ItemViewModel'之间执行'双向'转换。）。
MainWindowViewModel中的OnDelete事件处理程序永远不会被引发？编辑：实际上BtnDeleteClick中的ViewModel属性为null所以是的......当然。

顺便说一句 - 我使用Fody PropertyChanged。

MainWindow.xaml：

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:wpfApplication1="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="525"
        DataContext="{Binding RelativeSource={RelativeSource Self}}">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition></RowDefinition>
        </Grid.RowDefinitions>
        <Button Grid.Row="0" Width="100" Height="35" Content="Add" HorizontalAlignment="Left" Margin="10" Click="BtnAddClick"></Button>
        <Border Grid.Row="1" MinHeight="50">
            <ItemsControl ItemsSource="{Binding ViewModel.Items}">
                <ItemsControl.ItemsPanel>
                    <ItemsPanelTemplate>
                        <StackPanel/>
                    </ItemsPanelTemplate>
                </ItemsControl.ItemsPanel>
                <ItemsControl.ItemTemplate>
                    <DataTemplate>
                        <wpfApplication1:ItemView ViewModel="{Binding ., PresentationTraceSources.TraceLevel=High, Mode=TwoWay}"></wpfApplication1:ItemView>
                    </DataTemplate>
                </ItemsControl.ItemTemplate>
            </ItemsControl>
        </Border>
    </Grid>
</Window>

MainWindow.xaml.cs：

[ImplementPropertyChanged]
public partial class MainWindow
{
    public MainWindowViewModel ViewModel { get; set; }

    public MainWindow()
    {
        InitializeComponent();

        ViewModel = new MainWindowViewModel();
    }

    private void BtnAddClick(object sender, RoutedEventArgs e)
    {
        ViewModel.Add();
    }
}

MainWindowViewModel.cs：

[ImplementPropertyChanged]
public class MainWindowViewModel
{
    public ObservableCollection<ItemViewModel> Items { get; set; }

    public MainWindowViewModel()
    {
        Items = new ObservableCollection<ItemViewModel>();
    }

    public void Add()
    {
        var item = new ItemViewModel();
        item.OnDelete += (sender, args) =>
        {
            Debug.WriteLine("-- WAITING FOR THIS TO HAPPEN --");
            Items.Remove(item);
        };
        Items.Add(item);
    }
}

ItemViewModel.xaml：

<UserControl x:Class="WpfApplication1.ItemView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             DataContext="{Binding RelativeSource={RelativeSource Self}}">
    <Grid>
            <Button Width="100" Height="35" Content="Delete" Click="BtnDeleteClick"></Button>
    </Grid>
</UserControl>

ItemView.xaml.cs：

[ImplementPropertyChanged]
public partial class ItemView
{
    public static readonly DependencyProperty ViewModelProperty = DependencyProperty.Register
    (
        "ViewModel", typeof(ItemViewModel), typeof(ItemView), new UIPropertyMetadata(null)
    );

    public ItemViewModel ViewModel
    {
        get { return (ItemViewModel)GetValue(ViewModelProperty); }
        set { SetValue(ViewModelProperty, value); }
    }

    public ItemView()
    {
        InitializeComponent();
    }

    private void BtnDeleteClick(object sender, RoutedEventArgs e)
    {
        ViewModel.Delete();
    }
}

和ItemViewModel.cs：

[ImplementPropertyChanged]
public class ItemViewModel
{
    public event EventHandler OnDelete;

    public void Delete()
    {
        var handler = OnDelete;
        if (handler != null)
        {
            handler(this, new EventArgs());
        }
    }
}

Answer 1

你不应该设置

DataContext="{Binding RelativeSource={RelativeSource Self}}"

在ItemView的XAML中。它有效地破坏了MainWindow.xaml中的ViewModel="{Binding .}"绑定，因为DataContext不再是ItemsViewModel，而是ItemsView。

作为一项规则，您永远不应该显式设置UserControl的DataContext，因为所有＆＃34;外部＆＃34;然后，绑定需要明确的Source或RelativeSource值。

那就是说，你这么做太复杂了。您可以只使用带有删除命令的视图模型，并将Button的Command属性绑定到此命令，而不是在ItemsView中使用按钮单击处理程序。

看起来像这样：

public class ItemViewModel
{
    public string Name { get; set; }
    public ICommand Delete { get; set; }
}

public class MainViewModel
{
    public MainViewModel()
    {
        Items = new ObservableCollection<ItemViewModel>();
    }

    public ObservableCollection<ItemViewModel> Items { get; private set; }

    public void AddItem(string name)
    {
        Items.Add(new ItemViewModel
        {
            Name = name,
            Delete = new DelegateCommand(p => Items.Remove(p as ItemViewModel))
        });
    }
}

并将像这样使用：

<UserControl x:Class="WpfApplication1.ItemView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Grid>
        <Button Content="Delete"
                Command="{Binding Delete}"
                CommandParameter="{Binding}"/>
    </Grid>
</UserControl>

如何设置ItemsControl.ItemTemplate的依赖项属性并处理其事件

1 个答案: