wpf - 如何在设计时解析 ContentControl ContentTemplateSelector？

Question

为什么我无法在设计时解析 ContentControl ContentTemplateSelector？
(在运行时有效)
Designer(VS2010)显示异常:

System.Reflection.TargetInvocationException Exception has been thrown by the target of an invocation.

和

System.NullReferenceException Object reference not set to an instance of an object.

XAML:

<Window.Resources>
    <DataTemplate x:Key="Temp1">
       <TextBox TextWrapping="Wrap" Text="1" Height="20" Width="Auto"/>
    </DataTemplate>

    <local:TemplateSelector x:Key="mySelector"/>
    <Grid>
       <ContentControl ContentTemplateSelector="{StaticResource mySelector}">
          <ContentControl.Content>
               1
          </ContentControl.Content>
       </ContentControl>      
    </Grid>
 </Window.Resources>

C#:

    public class TemplateSelector : DataTemplateSelector
    {
        public override DataTemplate SelectTemplate(object item, DependencyObject container)
        {
             //int num = int.Parse(item.ToString());
             Window win = Application.Current.MainWindow;
             return win.FindResource("Temp1") as DataTemplate;//load template based on num...
         }

    }

Answer 1

H.B. Application.Current.MainWindow 在设计时为 null 是正确的。这是按名称检索资源的更好方法:

public override DataTemplate SelectTemplate( object item, DependencyObject container ) {
    var element = container as FrameworkElement;
    if ( element != null ) {
        var template = element.TryFindResource( "Temp1" ) as DataTemplate;
        if ( template != null ) {
            return template;
        }
    }
    return base.SelectTemplate( item, container );
}

不过，您的代码的其他部分仍然不完整，所以我希望您已经完成了。例如，您的 DataTemplate 应该具有绑定(bind)，而不是硬编码值。