如何告诉我的 DataTemplate 绑定到 PARENT ViewModel 中的属性? [英] How can I tell my DataTemplate to bind to a property in the PARENT ViewModel?

问题描述

我有以下 MainView.xaml 文件，可以很好地用作 MVVM 菜单切换器.我有这些对:

I've got the following MainView.xaml file that works well as a MVVM menu switcher. I've got these pairs:

• Page1View/Page1ViewModel
• Page2View/Page2ViewModel

在我的 MainViewModel 中，我用两个 ViewModel 填充 ObservableCollection，然后当用户单击 Next 按钮时，它会调用 MainViewModel 中的 NextPageCommand用一个新的 ViewModel 切换 CurrentPageViewModel，然后显示一个合适的 View，效果很好.

in my MainViewModel I fill an ObservableCollection with both ViewModels, then when the user clicks the Next button, it calls NextPageCommand in MainViewModel which switches out CurrentPageViewModel with a new ViewModel which is then displayed with an appropriate View, works nicely.

我还有一个 Menu，里面装满了 Observable 集合中 ViewModels 的所有标题，这也很好用.

I also have a Menu being filled with all the titles from the ViewModels in the Observable collection, which also works nicely.

但是，每个 MenuItem 都有一个 Command="{Binding SwitchPageCommand}" 应该在 MainViewModel 上调用 SwitchPageCommand 而不是在例如Page1ViewModel 或 Page2ViewModel.

However, each MenuItem has a Command="{Binding SwitchPageCommand}" which SHOULD call SwitchPageCommand on the MainViewModel and not on e.g. Page1ViewModel or Page2ViewModel.

那么我如何在模板中指明不绑定到当前的 ViewModel，而是绑定到 包含那个 ViewModel 的 ViewModel，例如像这样:

So how can I indicate in the template not to bind to the current ViewModel but the ViewModel which contains that ViewModel, e.g. something like this:

PSEUDO-CODE:

<DataTemplate x:Key="CodeGenerationMenuTemplate">
    <MenuItem 
        Command="{Binding <parentViewModel>.SwitchPageCommand}" 
        Header="{Binding Title}" 
        CommandParameter="{Binding Title}"/>
</DataTemplate>

这是MainViewModel:

<Window x:Class="TestMenu234.Views.MainView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:c="clr-namespace:TestMenu234.Commands"
    xmlns:vm="clr-namespace:TestMenu234.ViewModels"
    xmlns:v="clr-namespace:TestMenu234.Views"
    Title="Main Window" Height="400" Width="800">

    <Window.Resources>
        <DataTemplate x:Key="CodeGenerationMenuTemplate">
            <MenuItem Header="{Binding Title}" Command="{Binding SwitchPageCommand}" CommandParameter="{Binding Title}"/>
        </DataTemplate>
        <DataTemplate DataType="{x:Type vm:Page1ViewModel}">
            <v:Page1View/>
        </DataTemplate>
        <DataTemplate DataType="{x:Type vm:Page2ViewModel}">
            <v:Page2View/>
        </DataTemplate>
    </Window.Resources>

    <DockPanel>

        <Menu DockPanel.Dock="Top">
            <MenuItem Header="Code _Generation" ItemsSource="{Binding AllPageViewModels}"
                      ItemTemplate="{StaticResource CodeGenerationMenuTemplate}"/>
        </Menu>

        <StackPanel DockPanel.Dock="Top" Orientation="Horizontal">
            <Button Margin="5" Content="Next Page" Command="{Binding NextPageCommand}"/>
        </StackPanel>

        <ContentControl
            Content="{Binding CurrentPageViewModel}"/>

    </DockPanel>
</Window>

推荐答案

答案是这样的:

<DataTemplate x:Key="CodeGenerationMenuTemplate">
    <MenuItem 
        Header="{Binding Title}" 
        Command="{Binding DataContext.SwitchPageCommand,
    RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Menu}}}" 
        CommandParameter="{Binding Title}"/>
</DataTemplate>

我刚刚看到 Nir ​​给了我解决上述问题的语法:MVVM 中构建显示各种页面的菜单的最佳方法是什么?.

I just saw that Nir had given me the syntax to solve the above issue on this question: What is the best way in MVVM to build a menu that displays various pages?.

这篇关于如何告诉我的 DataTemplate 绑定到 PARENT ViewModel 中的属性?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！