当 UserControl 具有 DataContext 时，UserControl 的 DependencyProperty 为 null [英] UserControl's DependencyProperty is null when UserControl has a DataContext

问题描述

我在我的视图中添加了一个 DependencyProperty，绑定到 DependencyProperty 有效，但前提是我没有设置 DataContext.

I have added a DependencyProperty to my View, binding to the DependencyProperty works, but only if I do not also set the DataContext.

GenericView.xaml

<UserControl x:Class="GenericProject.View.GenericView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <StackPanel>
        <Button Command="{Binding VMFactory.CreateViewModelCommand, RelativeSource={RelativeSource AncestorType={x:Type UserControl}}}" />
        <TextBox IsEnabled="False" Text="{Binding SomeProperty, Mode=OneWay}" />
    </StackPanel>
</UserControl>

GenericView.xaml.cs

public partial class GenericView : UserControl
{
    // The DependencyProperty for VMFactory.
    public static readonly DependencyProperty VMFactoryProperty = DependencyProperty.Register("VMFactory", typeof(VMFactoryViewModel<GenericViewModel>), typeof(GenericView));

    public VMFactoryViewModel<GenericViewModel> VMFactory
    {
        get { return (VMFactoryViewModel<GenericViewModel>)GetValue(VMFactoryProperty); }
        set { SetValue(VMFactoryProperty, value); }
    }

    public GenericView()
    {
        InitializeComponent();
    }
}

这里我创建了两个视图来说明手头的问题.第一个视图中的 VMFactory 绑定将失败，因为我设置了 DataContext.第二种观点会成功，这种行为的原因是什么?

Here I am creating two views to illustrate the issue at hand. The VMFactory binding in the first view will fail because I have DataContext set. The second view will succeed, what is the cause of this behavior?

MainPage.xaml

<vw:GenericView DataContext="{Binding Generic}" VMFactory="{Binding GenericFactory}" />
<vw:GenericView VMFactory="{Binding GenericFactory}" />

推荐答案

我有一个可行的解决方案，似乎控件的属性是相对于控件的 DataContext 绑定的?

I've got a working solution, it seems as though properties of a control are bound relative to the DataContext of the control?

我当然知道控件中的项目将相对于 DataContext 绑定，但我显然以前从未以这种方式使用过控件，并且不明白控件的属性也会继承设置的 DataContext 的范围.基本上我视图中的所有内容都是正确的，但与我的 DependencyProperty 的绑定失败了.

I was certainly aware items within the control would be bound relative to the DataContext, but I apparently have never used a control in this way before and did not understand that properties of the control would also inherit the scope of the set DataContext. Essentially everything within my View was correct, but the binding to my DependencyProperty was failing.

GenericView.xaml

<!-- Everything in here was correct. -->
<UserControl x:Class="GenericProject.View.GenericView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <StackPanel>
        <Button Command="{Binding VMFactory.CreateViewModelCommand, RelativeSource={RelativeSource AncestorType={x:Type UserControl}}}" />
        <TextBox IsEnabled="False" Text="{Binding SomeProperty, Mode=OneWay}" />
    </StackPanel>
</UserControl>

MainPage.xaml

<!-- This is where I messed up earlier, VMFactory requires a relative binding. -->
<vw:GenericView DataContext="{Binding Generic}"
                VMFactory="{Binding DataContext.GenericFactory, RelativeSource={RelativeSource AncestorType={x:Type Page}}}" />

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