XAML绑定的灾难性失败 [英] Catastrophic failure in xaml binding

问题描述

我正在开发Windows 10 Universal App。我的代码如下：

I am developing Windows 10 Universal App. I have code below:

xaml：

<Page
    x:Class="MyProject.BlankPage1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:MyProject"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
>
    <ItemsControl ItemsSource="{Binding}">
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <Canvas Background="Purple"/>
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
        <ItemsControl.ItemContainerStyle>
            <Style TargetType="ContentPresenter">
                <Setter Property="Canvas.Left" Value="{Binding X}"/>
                <Setter Property="Canvas.Top" Value="{Binding Y}"/>
            </Style>
        </ItemsControl.ItemContainerStyle>
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Rectangle Fill="Red" Width="50" Height="50"/>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</Page>

和后面的代码：

namespace MyProject
{
    public sealed partial class BlankPage1 : Page
    {
        public BlankPage1()
        {
            DataContext =
                new[]
                {
                    new { X = 50.0, Y = 100.0 },
                    new { X = 220.0, Y = 170.0 }
                };
            InitializeComponent();
        }
    }
}

不幸的是，矩形不会显示在窗口中。我遇到编译错误：

Unfortunatelly, the rectangles does not show in the window. I am getting compilation error:

Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED))

分配给画布可协调xaml中的静态数字按预期工作。

Assigning to Canvas coordinates static numbers in xaml works as expected.

为什么出错

推荐答案

我只是在构建通用Windows平台应用程序时偶然发现了此问题。

I just stumbled upon this issue myself, while building a Universal Windows Platform app.

做了一些谷歌搜索，发现这篇文章。

Did some googling, found this article.

它非常有帮助。我将他的 SetterValueBindingHelper 类复制到我自己的项目中。之后，我做了1次调整，因为

It was very helpful. I copied his SetterValueBindingHelper class into my own project. After that, I made 1 adjustment, because

type = System.Type.GetType(item.Type).GetTypeInfo();

在执行 Type = Canvas 在XAML绑定中。它首先尝试在当前程序集中找到类 Canvas 。这将返回 null ，然后调用 .GetTypeInfo（）引发NullReferenceException。

gave an exception when you do Type="Canvas" in the XAML binding. It first tries to find the class Canvas in the current assembly. This returns null, and then it calls .GetTypeInfo() throwing a NullReferenceException.

在其上实现了C＃6.0的新 Null-Conditional运算符，从而解决了此问题。紧接着检查 type 是否为空的代码，然后遍历所有已加载的程序集以找到 Canvas 。

Implemented C# 6.0's new Null-Conditional Operator on it, and that solved this issue. The code immediately after checks if type is null, and then goes through all loaded assemblies to find the Canvas.

type = System.Type.GetType(item.Type)?.GetTypeInfo();

他的第二个用法示例与将其与 Canvas 元素。

His second usage example is oddly specifically related to using it with a Canvas element.

我的Project VisualDesigner中的另一个示例：

Another example from my Project VisualDesigner:

这是基于他的示例的我的最终XAML：

Here's my final XAML, based on his example:

<ItemsControl Grid.Column="1" ItemsSource="{Binding CanvasItems}">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <Canvas />
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
    <ItemsControl.ItemContainerStyle>
        <Style TargetType="ContentPresenter">
            <Setter Property="helpers:SetterValueBindingHelper.PropertyBinding">
                <Setter.Value>
                    <helpers:SetterValueBindingHelper>
                        <helpers:SetterValueBindingHelper Type="Canvas" Property="Left" Binding="{Binding WindowX, Mode=TwoWay}" />
                        <helpers:SetterValueBindingHelper Type="Canvas" Property="Top" Binding="{Binding WindowY, Mode=TwoWay}" />
                    </helpers:SetterValueBindingHelper>
                </Setter.Value>
            </Setter>
        </Style>
    </ItemsControl.ItemContainerStyle>
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <applicationwindow:ApplicationWindow Width="{Binding WindowWidth}" Height="{Binding WindowHeight}" DataContext="{Binding}" />
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

helpers：引用 SetterValueBindingHelper 在其中。 ApplicationWindow 是自定义的UserControl。 CanvasItems 是 ObservableCollection< ApplicationWindowViewModel> ，这是我的 ApplicationWindowViewModel ：

helpers: refers to the namespace the SetterValueBindingHelper is in. ApplicationWindow in my case is a custom UserControl. CanvasItems is an ObservableCollection<ApplicationWindowViewModel>, and this is my ApplicationWindowViewModel:

[ImplementPropertyChanged]
public class ApplicationWindowViewModel : ViewModelBase
{
    public string Title { get; set; }

    public double WindowX { get; set; } = 10;

    public double WindowY { get; set; } = 10;

    public int WindowWidth { get; set; } = 300;

    public int WindowHeight { get; set; } = 200;
}

在此示例中，我使用 Fody.PropertyChanged 来处理X / Y / Width / Height属性上的属性更改事件，如果您不使用此程序包，请不要忘记实现自己的PropertyChanged事件处理程序等。

In this example I use Fody.PropertyChanged to handle the property changed events on the X/Y/Width/Height properties, if you're not using this package, don't forget to implement your own PropertyChanged event handlers, etc.

这篇关于XAML绑定的灾难性失败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！