Question

我有一个强类型的View类，我的所有UserControl都来自它。看起来或多或少是这样的：

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; }
    }
}

关于AutoCreateDataContext的一点是新的...并且是我的问题的来源。将它添加到View<TContext>基类本身并没有引起任何问题......但是一旦我在一个派生视图中将值设置为true：

<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会引发以下异常：

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 ....

一旦从标记中删除AutoCreateDataContext = True，它就会再次正常工作。没有内部异常或进一步的异常细节。我该如何调试/解决此问题？

Answer 1

我做了一些猜测，然后进行了反汇编，发现它是WPF如何处理在泛型DependencyObjects上声明的DependencyProperties的错误（比如我的View<T>）。

制作一个抽象的非泛型基类（称为View，which View<T> now inherits from）并在那里声明我的DependencyProperties。问题解决了。

我想我已经习惯了微软质量的糟糕程度......所以我实际上已经开始认识到像这样的bug的趋势。

WPF UserControl InitializeComponent异常

1 个答案: