在Window.Resources中的数据模板中绑定拥有窗口的视图模型中的属性 [英] Binding to property in owning window's viewmodel within a DataTemplate in Window.Resources

问题描述

我在窗口的资源部分中有一个DataTemplate，它可以使用ContextMenu创建一个TextBlock。我希望能够设置从我的窗口的视图模型中是否可以看到ContextMenu中的MenuItem。我尝试通过设置 ElementName 访问窗口的DataContext，还尝试设置 RelativeSource ，但是两种方法都导致绑定错误。我不确定我还能尝试什么。

I have a DataTemplate within my Window's Resources section that creates a TextBlock with a ContextMenu. I want to be able to set whether a MenuItem within the ContextMenu is visible from within my Window's view model. I have tried accessing the DataContext of the Window by setting ElementName, and also tried setting RelativeSource, but both approaches resulted in binding errors. I'm not sure what else I can try.

我创建了一个小示例，显示了我正在尝试做的事情：

I have created a small example that shows what I'm trying to do:

XAML：

<Window x:Class="DataTemplateTest.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">


<Window.Resources>
    <ResourceDictionary>
        <DataTemplate x:Key="TestDataTemplate">
            <TextBlock Text="{Binding}">
                <TextBlock.ContextMenu>
                    <ContextMenu>
                        <MenuItem Header="Test" Visibility="{Binding Path=DataContext.MenuItemVisible, ElementName=Root}"/>
                    </ContextMenu>
                </TextBlock.ContextMenu>
            </TextBlock>
        </DataTemplate>
    </ResourceDictionary>
</Window.Resources>

<ScrollViewer x:Name="Root">
    <ItemsControl ItemsSource="{Binding Path=Items}" ItemTemplate="{StaticResource TestDataTemplate}" />
</ScrollViewer>

后面的代码：

using System.Collections.Generic;
using System.ComponentModel;
using System.Windows;

namespace DataTemplateTest
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        protected readonly MainWindowViewModel vm;

        public MainWindow()
        {
            InitializeComponent();
            vm = new MainWindowViewModel();
            DataContext = vm;
        }
    }

    public class MainWindowViewModel : INotifyPropertyChanged
    {
        private Visibility menuItemVisible = Visibility.Hidden;
        public Visibility MenuItemVisible { get { return menuItemVisible; } set { menuItemVisible = value; NotifyPropertyChanged("MenuItemVisible"); } }

        public List<string> Items { get; set; }

        public MainWindowViewModel()
        {
            Items = new List<string>() { "Alpha", "Beta", "Gamma" };
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

我得到的错误是

System.Windows.Data错误：4：找不到引用'ElementName = Root'的绑定源。
BindingExpression：Path = DataContext.MenuItemVisible; DataItem = null;
目标元素是 MenuItem（名称=）；目标属性是
'Visibility'（类型为'Visibility'）

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=Root'. BindingExpression:Path=DataContext.MenuItemVisible; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'Visibility' (type 'Visibility')

在绑定中设置RelativeSource而不是ElementName时：

When I set RelativeSource instead of ElementName in the binding:

RelativeSource={RelativeSource Mode=FindAncestor, 
                AncestorType={x:Type ScrollViewer}}

我收到以下错误：

System.Windows.Data错误：4：找不到
参考'RelativeSource FindAncestor，
AncestorType ='System.Windows.Controls.ScrollViewer'，
AncestorLevel ='1的绑定源。
BindingExpression：Path = DataContext.MenuItemVisible; DataItem = null;
目标元素是 MenuItem（名称=）；目标属性是
可见性（类型为可见性）

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Controls.ScrollViewer', AncestorLevel='1''. BindingExpression:Path=DataContext.MenuItemVisible; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'Visibility' (type 'Visibility')

推荐答案

I在这里找到了答案：

因此，我需要做的所有工作才能访问设置了窗口的DataContext：

So all I had to do to access the window's DataContext was set:

Source={x:Reference Name=Root}

找到了为什么在这种情况下ElementName不起作用的说明此处。具体来说：

An explanation of why ElementName does not work in this case is found here. Specifically:

可能最简单的例子是我们没有继承上下文链接的地方是>随机属性元素：

Probably the simplest example of where we don't have inheritance context links is across > random property elements:

<Button>
  <Button.ContextMenu>
    <ContextMenu/>
  </Button.ContextMenu>
</Button>

ContextMenu既不是Button的视觉子元素也不是逻辑子元素，也不是上面列出的继承上下文案例之一（ContextMenu是不是Freezable）。

ContextMenu is neither a visual nor logical child of Button, nor is it one of the inheritance context cases listed above (ContextMenu is not a Freezable).

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