将事件处理程序添加到 WPF DataGrid 会引发 NullReferenceException

发布于 2024-12-03 11:20:40 字数 1963 浏览 0 评论 0原文

我不确定我写的 DataGrid 有什么问题。内容显示正确，但是当我尝试添加 OnSelectionChanged 事件处理程序时，发生了奇怪的情况。请帮助我！

首先，没有以下问题：

<DataGrid ItemsSource="{Binding XPath=services/service}" AutoGenerateColumns="False" Padding="2">
      <DataGrid.Columns>
          <DataGridTextColumn Header=" Service Name " Binding="{Binding XPath=name}" Width="300"/>
          <DataGridTextColumn Header=" Status " Binding="{Binding XPath=status}" />
      </DataGrid.Columns>
</DataGrid>

这里的服务/服务来自我的外部 XML 文件。我在文档中使用了 XmlDataProvider 资源。在该 XML 中，某些“services”标签具有许多“service”子元素；一些“服务”标签根本没有任何子标签（想知道这是否是问题的原因）。

因此，最终的 UI 是一些包含所有行和列的数据网格。一些数据网格仅显示标题。

现在我添加：

<DataGrid ItemsSource="{Binding XPath=services/service}" AutoGenerateColumns="False" Padding="2"
SelectionChanged="DataGrid_SelectionChanged">

并在代码中添加一个空方法：

private void DataGrid_SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
    {


    }

现在我执行，并抛出异常

System.NullReferenceException 未处理消息=未将对象引用设置为对象的实例。来源=ForeFront 支持监视器 2 堆栈跟踪：在 h:\Personal\Visual Studio 2010\Projects\ForeFront 支持监视器 2\ForeFront 支持监视器 2\MainWindow.xaml 中的 FSM.MainWindow.System.Windows.Markup.IStyleConnector.Connect(Int32 connectionId, Object target)：第 42 行在 System.Windows.FrameworkTemplate.LoadTemplateXaml（XamlReader templateReader，XamlObjectWriter currentWriter）在 System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlObjectWriter objectWriter) 在 System.Windows.FrameworkTemplate.LoadOptimizedTemplateContent（DependencyObject 容器、IComponentConnector componentConnector、IStyleConnector styleConnector、List1affectedChildren、UncommonField1 templatedNonFeChildrenField）在 System.Windows.FrameworkTemplate.LoadContent（DependencyObject 容器，List`1affectedChildren）...

原文

I'm not sure what's wrong with the DataGrid I've written. The contents show up correctly but when I try to add in a OnSelectionChanged event handler, sth odd happens.Please help me!

Firstly, no problems below:

<DataGrid ItemsSource="{Binding XPath=services/service}" AutoGenerateColumns="False" Padding="2">
      <DataGrid.Columns>
          <DataGridTextColumn Header=" Service Name " Binding="{Binding XPath=name}" Width="300"/>
          <DataGridTextColumn Header=" Status " Binding="{Binding XPath=status}" />
      </DataGrid.Columns>
</DataGrid>

Here services/service are from my external XML file. I used XmlDataProvider resource in the document. In that XML, some 'services' tag has many 'service' children elements; some 'services' tag does not have any children at all (wondering if this is the cause of problem).

So the resultant UI is some of the datagrids contain all the rows and columns. some of the datagrids only show the headers.

Now I add in this:

<DataGrid ItemsSource="{Binding XPath=services/service}" AutoGenerateColumns="False" Padding="2"
SelectionChanged="DataGrid_SelectionChanged">

And put in a empty method on the code:

private void DataGrid_SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
    {


    }

Now I execute, and an exception is thrown

System.NullReferenceException was unhandled
Message=Object reference not set to an instance of an object.
Source=ForeFront Support Monitor 2
StackTrace:
at FSM.MainWindow.System.Windows.Markup.IStyleConnector.Connect(Int32 connectionId, Object target) in h:\Personal\Visual Studio 2010\Projects\ForeFront Support Monitor 2\ForeFront Support Monitor 2\MainWindow.xaml:line 42
at System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlReader templateReader, XamlObjectWriter currentWriter)
at System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlObjectWriter objectWriter)
at System.Windows.FrameworkTemplate.LoadOptimizedTemplateContent(DependencyObject container, IComponentConnector componentConnector, IStyleConnector styleConnector, List1 affectedChildren, UncommonField1 templatedNonFeChildrenField)
at System.Windows.FrameworkTemplate.LoadContent(DependencyObject container, List`1 affectedChildren)...