data bind question, help pls 🌞

[yanwuguangjun]

 <TabControl ItemsSource="{Binding Project.PreDefineModes}">
     <TabControl.ItemTemplate>
         <DataTemplate>
             <TextBlock Text="{Binding Name}" FontWeight="Bold" />
         </DataTemplate>
     </TabControl.ItemTemplate>

     <TabControl.ContentTemplate>
         <DataTemplate>
             <StackPanel>
              <StackPanel Orientation="Horizontal"> 
                  <CheckBox Content="Option One" IsChecked="True" />
                  <CheckBox Content="Option One" IsChecked="True" />
               </StackPanel>

               <DataGrid Margin="20" 
                         ItemsSource="{Binding Pages}" >
                   <DataGrid.Columns>
                       <DataGridTextColumn Header="Path" Width="2*" Binding="{Binding path}" />
                   </DataGrid.Columns>
               </DataGrid>
           </StackPanel>
         </DataTemplate>
     </TabControl.ContentTemplate>
 </TabControl>

the project struct is

    public class CustomMode
    {
        public string Name { get; set; } = "";
        public string Description { get; set; } = "";
        public List<Page> Pages { get; set; } = [];
    }

    public class Project
    {
        public string Name { get; set; }
        public string Description { get; set; }
        public List<CustomMode> PreDefineModes { get; set; } = [];
    }

    public class Page 
    {
        public string path { get; set; }
    }

the error in the line 16 ItemsSource="{Binding Pages}"
preview error

0:48:47.995 [Error] 21432 UpdateXamlResult error
10:48:47:997	System.Xaml.XamlException: One or more errors occurred. (Unable to resolve property or method of name 'Pages' on type 'XamlX.TypeSystem.XamlPseudoType'. Line 34, position 37.) (Unable to resolve property or method of name 'Pages' on type 'XamlX.TypeSystem.XamlPseudoType'. Line 34, position 37.)
10:48:47:998	10:48:47.997 [Error] 21432 UpdateXamlResult error details: "System.AggregateException: One or more errors occurred. (Unable to resolve property or method of name 'Pages' on type 'XamlX.TypeSystem.XamlPseudoType'. Line 34, position 37.) (Unable to resolve property or method of name 'Pages' on type 'XamlX.TypeSystem.XamlPseudoType'. Line 34, position 37.)
10:48:47:998	 ---> XamlX.XamlTransformException: Unable to resolve property or method of name 'Pages' on type 'XamlX.TypeSystem.XamlPseudoType'. Line 34, position 37.
10:48:47:998	   at Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.XamlIlBindingPathHelper.TransformBindingPath(AstTransformationContext context, IXamlLineInfo lineInfo, Func`1 startTypeResolver, IXamlType selfType, IEnumerable`1 bindingExpression)
10:48:47:998	   at Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.XamlIlBindingPathHelper.UpdateCompiledBindingExtension(AstTransformationContext context, XamlAstConstructableObjectNode binding, Func`1 startTypeResolver, IXamlType selfType)
10:48:47:998	   at Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers.AvaloniaXamlIlDataContextTypeTransformer.InferDataContextOfPresentedItem(AstTransformationContext context, XamlAstConstructableObjectNode on, XamlAstConstructableObjectNode parentObject, String propertyName)
10:48:47:998	   at Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers.AvaloniaXamlIlDataContextTypeTransformer.Transform(AstTransformationContext context, IXamlAstNode node)
10:48:47:998	   at XamlX.Transform.AstTransformationContext.ContextXamlAstVisitor.Visit(IXamlAstNode node)
10:48:47:998	   --- End of inner exception stack trace ---
10:48:47:998	   at XamlX.ContextDiagnosticExtensions.ThrowExceptionIfAnyError(IEnumerable`1 diagnostics)
10:48:47:998	   at Avalonia.Markup.Xaml.XamlIl.AvaloniaXamlIlRuntimeCompiler.LoadGroupSreCore(IReadOnlyCollection`1 documents, RuntimeXamlLoaderConfiguration configuration)
10:48:47:998	   at Avalonia.Markup.Xaml.XamlIl.AvaloniaXamlIlRuntimeCompiler.LoadSreCore(RuntimeXamlLoaderDocument document, RuntimeXamlLoaderConfiguration configuration)
10:48:47:998	   at Avalonia.Markup.Xaml.XamlIl.AvaloniaXamlIlRuntimeCompiler.LoadSre(RuntimeXamlLoaderDocument document, RuntimeXamlLoaderConfiguration configuration)
10:48:47:998	   at Avalonia.Markup.Xaml.XamlIl.AvaloniaXamlIlRuntimeCompiler.Load(RuntimeXamlLoaderDocument document, RuntimeXamlLoaderConfiguration configuration)
10:48:47:998	   at Avalonia.Designer.HostApp.DesignXamlLoader.Load(RuntimeXamlLoaderDocument document, RuntimeXamlLoaderConfiguration configuration)
10:48:47:998	   at Avalonia.DesignerSupport.DesignWindowLoader.LoadDesignerWindow(String xaml, String assemblyPath, String xamlFileProjectPath, Double renderScaling)
10:48:47:998	   at Avalonia.DesignerSupport.Remote.RemoteDesignerEntryPoint.<>c.<OnTransportMessage>b__17_0(Object arg)
10:48:47:998	 ---> (Inner Exception #1) XamlX.XamlTransformException: Unable to resolve property or method of name 'Pages' on type 'XamlX.TypeSystem.XamlPseudoType'. Line 34, position 37.
10:48:47:998	   at Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.XamlIlBindingPathHelper.TransformBindingPath(AstTransformationContext context, IXamlLineInfo lineInfo, Func`1 startTypeResolver, IXamlType selfType, IEnumerable`1 bindingExpression)
10:48:47:998	   at Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.XamlIlBindingPathHelper.UpdateCompiledBindingExtension(AstTransformationContext context, XamlAstConstructableObjectNode binding, Func`1 startTypeResolver, IXamlType selfType)
10:48:47:998	   at Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers.AvaloniaXamlIlBindingPathTransformer.Transform(AstTransformationContext context, IXamlAstNode node)
10:48:47:998	   at XamlX.Transform.AstTransformationContext.ContextXamlAstVisitor.Visit(IXamlAstNode node)<---

[thevortexcloud]

To clarify:

• This is an issue with the previewer or a run time error?
• Are you using compiled bindings or reflection bindings?
• What are you trying to do?

[tobyfirth]

If you change the DataTemplate instances so that the DataType is specified then it should work. I could make your sample code work when I specified the DataType to use for the template.

<DataTemplate DataType="vm:CustomMode">
    <!-- The Template -->
</DataTemplate>

When using compiled bindings that DataType must be specified. I was getting the same error as you from the previewer before making the change. There should also be a compiler error when trying to compile.

The documentation mentions this but only in the section about Compiled Bindings not in the section on Data Templates. There should probably be a note there mentioning about when using compiled bindings.