我怎样才能绑定到一个通用的Windows应用程序模板内的空值？ [英] How can I bind to a null value inside a template in a Universal Windows App?

问题描述

在你回答之前，看的这个帖子。

Before you answer, look at this post.

的获得一个回答首先可以解决以下问题。的

这是刚开始使用Windows 10有问题（通用应用程序）。在Windows 8.1，和所有其他XAML技术，这种技术完美地工作。下面是一片空白通用的应用程序项目的设置：

This is a problem that just started with Windows 10 (Universal Apps). In Windows 8.1, and every other XAML technology, this technique worked flawlessly. Here's the setup in a blank universal app project:

1。静态类附加属性

创建容纳类型的附加属性的类刷。把项目中的这个任意位置。

Create a class that houses an attached property of type Brush. Put this anywhere in the project.

public static class MySettings
{
    public static Brush GetAccentBrush(DependencyObject d)
    {
        return (Brush)d.GetValue(AccentBrushProperty);
    }

    public static void SetAccentBrush(DependencyObject d, Brush value)
    {
        d.SetValue(AccentBrushProperty, value);
    }

    public static readonly DependencyProperty AccentBrushProperty = DependencyProperty.RegisterAttached(
        "AccentBrush",
        typeof(Brush),
        typeof(MySettings),
        null
        );
}

2。一个控件添加到您的MainPage.xaml中使用附加属性

在主界面中，添加 ContentControl中与具有电网与背景颜色设置为口音刷自定义模板。该口音刷设置在样式

In the main page, add a ContentControl with a custom template that has a Grid with its background color set to the accent brush. The accent brush is set in a style.

<Page x:Class="UniversalTest.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      xmlns:local="using:UniversalTest"
      mc:Ignorable="d">
    <Page.Resources>
        <Style x:Key="MyControl"
               TargetType="ContentControl">
            <Setter Property="local:MySettings.AccentBrush"
                    Value="Green" /> <!-- Setting value here -->
        </Style>
    </Page.Resources>

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

        <ContentControl Style="{StaticResource MyControl}">
            <ContentControl.Template>
                <ControlTemplate TargetType="ContentControl">
                    <Grid Background="{TemplateBinding local:MySettings.AccentBrush}"> <!-- Using value here -->
                        <TextBlock Text="Howdy World!" />
                    </Grid>
                </ControlTemplate>
            </ContentControl.Template>
        </ContentControl>

    </Grid>
</Page>

如果您现在运行应用程序，它会显示一个绿色的背景。一切正常。但是，如果将值设置为 {X：空} ，它抛出一个异常

If you run the app now, it will show up with a green background. Everything works. However, if you set the value as {x:Null}, it throws an exception.

<Page.Resources>
    <Style x:Key="MyControl"
            TargetType="ContentControl">
        <Setter Property="local:MySettings.AccentBrush"
                Value="{x:Null}" /> <!-- Null value here -->
    </Style>
</Page.Resources>

有没有人愿意采取射击在此？

Would anyone like to take a shot at this?

推荐答案

有关记录，这个问题似乎已经得到修复。我的项目引用通用Windows版本10.0.10240.0。刷设置为{X：空}。由原始的海报按预期工作。

For the record, this issue appears to have been fixed. My project references Universal Windows version 10.0.10240.0. Setting the brush to {x:Null} as described by the original poster works as expected.

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