WPF UserControl InitializeComponent异常 [英] WPF UserControl InitializeComponent Exception

问题描述

我有一个强烈类型化的View类，我所有的UserControl都派生自该类.看起来或多或少是这样的:

I have a strongly typed View class that all my UserControls derive from. It looks more or less like this:

public class View<TContext> : UserControl 
{

    /// <summary>
        /// Gets or sets a value indicating whether to auto create the data context type.
        /// </summary>
    public static DependencyProperty AutoCreateDataContextProperty = DependencyProperty.Register("AutoCreateDataContext", typeof(bool), typeof(View<TContext>), new PropertyMetadata(false));
    /// <summary>
    /// Gets or sets a value indicating whether to auto create the data context type.
    /// </summary>
    /// <value>
    ///     <c>true</c> if [auto resolve data context]; otherwise, <c>false</c>.
    /// </value>
    public bool AutoCreateDataContext
    {
        get { return (bool)GetValue(AutoCreateDataContextProperty); }
        set { SetValue(AutoCreateDataContextProperty, value); }
    }

    /// <summary>
    /// Gets or sets the view model.
    /// </summary>
    /// <value>
    /// The view model.
    /// </value>
    public new TContext DataContext
    {
        get
        {
            if (AutoCreateDataContext && !DesignerProperties.GetIsInDesignMode(new ContentControl()))
            {
                base.DataContext = ServiceProvider.Current.GetService<TContext>();
            }
            return (TContext)base.DataContext;
        }
        set { base.DataContext = value; }
    }
}

有关AutoCreateDataContext的内容是新的，这是我提出问题的根源.将其添加到 View< TContext> 基类本身并不会引起任何问题...但是一旦我在派生的Views中将其值设置为true

The bit about AutoCreateDataContext is new...and is the source of my question. Adding this to the View<TContext> base class hasn't caused any problems itself...but once I set the value to true in one of my derived Views:

<s:View x:TypeArguments="local:PersonSearchViewModel"
    x:Class="PersonSearchView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" ...
             Height="600" Width="800" Background="White" AutoCreateDataContext="True">

此视图的

InitializeComponent引发以下异常:

InitializeComponent for this view throws the following exception:

System.NullReferenceException occurred
  Message=Object reference not set to an instance of an object.
  Source=PresentationFramework
  StackTrace:
       at System.Windows.Markup.WpfXamlLoader.TransformNodes(XamlReader xamlReader, XamlObjectWriter xamlWriter, Boolean onlyLoadOneNode, Boolean skipJournaledProperties, Boolean shouldPassLineNumberInfo, IXamlLineInfo xamlLineInfo, IXamlLineInfoConsumer xamlLineInfoConsumer, XamlContextStack`1 stack, IStyleConnector styleConnector)
       at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
       at System.Windows.Markup.WpfXamlLoader.LoadBaml(XamlReader xamlReader, Boolean skipJournaledProperties, Object rootObject, XamlAccessLevel accessLevel, Uri baseUri)
       at System.Windows.Markup.XamlReader.LoadBaml(Stream stream, ParserContext parserContext, Object parent, Boolean closeStream)
       at System.Windows.Application.LoadComponent(Object component, Uri resourceLocator)
       at ....

一旦我从标记中删除了AutoCreateDataContext = True，它就会再次正常运行.没有内部异常或进一步的异常详细信息.我该如何调试/解决这个问题?

As soon as I remove the AutoCreateDataContext=True from the markup, it works fine again. There is no inner exception or further exception detail. How can I debug/resolve this?

推荐答案

我进行了一些猜测，然后进行了分解，发现这是WPF如何处理在通用DependencyObjects上声明的DependencyProperties的错误(例如，我的 View< T>).

I did some guessing and then disassembling and found it to be a bug in how WPF handles DependencyProperties declared on generic DependencyObjects (like my View<T>).

制作了一个抽象的非通用基类(称为View， View< T>现在从中继承)，并在那里声明了我的DependencyProperties.问题解决了.

Made an abstract non-generic base class (called View, which View<T> now inherits from) and declared my DependencyProperties there instead. Problem solved.

我想我已经习惯了Microsoft的质量有多么差...所以我实际上已经开始认识到这种bug的趋势.

I guess I've gotten used to just how poor Microsoft quality is...so I've actually started recognizing trends in bugs like this.

这篇关于WPF UserControl InitializeComponent异常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！