ComboBox Binding in DataGrid, selecteditem did not display in combobox

[gtcyril]

What I want to ask is that why the combobox binding in datagrid can not binding selectitem when the main window shows. The dropdownlist has values, but the selecteditem did not display in combobox.

Here is my code:
MainWindowViewModel:

public partial class MainWindowViewModel : ViewModelBase
{
    public MainWindowViewModel()
    {
        Foos =
        [
            new() { Id = 1, Name = "1" },
            new() { Id = 2, Name = "2" },
            new() { Id = 3, Name = "3" },
        ];
        Elements =
        [
            new() { Id = 1, Foo = Foos[0] },
            new() { Id = 2, Foo = Foos[1] },
            new() { Id = 3, Foo = Foos[2] },
        ];
    }

    [ObservableProperty]
    ObservableCollection<Foo> _foos = [];

    [ObservableProperty]
    ObservableCollection<Element> _elements = [];
}

public partial class Foo : ObservableObject
{
    public int Id { get; set; }

    [ObservableProperty]
    private string? _name;
}

public partial class Element : ObservableObject
{
    public int Id { get; set; }

    [ObservableProperty]
    private Foo? _foo;
}

axmal:

<DataGrid ItemsSource="{Binding Elements}">
        <DataGrid.Columns>
            <DataGridTemplateColumn>
                <DataTemplate>
                    <ComboBox
                        ItemsSource="{Binding $parent[Window].((vm:MainWindowViewModel)DataContext).Foos}"
                        SelectedValue="{Binding Foo}"
                        DisplayMemberBinding="{Binding Name}" />
                </DataTemplate>
            </DataGridTemplateColumn>
        </DataGrid.Columns>
</DataGrid>

[rabbitism]

Is it working outside DataGrid?

[gtcyril]

Is it working outside DataGrid?

您好, 董老师, 就跟您说中文了, 我改了一下代码, 外部增加了一个Combobox, 增加了一个SelectedFoo属性, 绑定是正常的, 劳烦帮忙看下在DataGrid这种情况下, 应该怎么处理

    <StackPanel Spacing="20" Margin="20">
        <ComboBox
            ItemsSource="{Binding Foos}"
            DisplayMemberBinding="{Binding Name}"
            SelectedValue="{Binding SelectedFoo}" />
        <DataGrid ItemsSource="{Binding Elements}">
            <DataGrid.Columns>
                <DataGridTemplateColumn>
                    <DataTemplate>
                        <ComboBox
                            ItemsSource="{Binding $parent[Window].((vm:MainWindowViewModel)DataContext).Foos}"
                            DisplayMemberBinding="{Binding Name}"
                            SelectedValue="{Binding Foo}" />
                    </DataTemplate>

                </DataGridTemplateColumn>
            </DataGrid.Columns>
        </DataGrid>
    </StackPanel>

 public partial class MainWindowViewModel : ViewModelBase
 {
     public MainWindowViewModel()
     {
         Foos =
         [
             new() { Id = 1, Name = "1" },
             new() { Id = 2, Name = "2" },
             new() { Id = 3, Name = "3" },
         ];
         Elements =
         [
             new() { Id = 1, Foo = Foos[0] },
             new() { Id = 2, Foo = Foos[1] },
             new() { Id = 3, Foo = Foos[2] },
         ];
         SelectedFoo = Foos[0];
     }
     
     [ObservableProperty]
     ObservableCollection<Foo> _foos = [];

     [ObservableProperty]
     ObservableCollection<Element> _elements = [];

     [ObservableProperty]
     Foo? _selectedFoo;
 }

 public partial class Foo : ObservableObject
 {
     public int Id { get; set; }

     [ObservableProperty]
     private string? _name;
 }

 public partial class Element : ObservableObject
 {
     public int Id { get; set; }

     [ObservableProperty]
     private Foo? _foo;
 }

[pygmypenguin]

This has been happening to me as well. Any movement?

<StackPanel Name="Root">
    <ItemsControl ItemsSource="{Binding MyItems}">
        <ItemsControl.ItemTemplate>
            <DataTemplate x:DataType="local:MyItemType">
                <ComboBox ItemsSource="{Binding $parent[StackPanel].((local:MyVmType)DataContext).ComboBoxOptions}"
                                     SelectedItem="{Binding Selection}"
                                     SelectionChanged="{ComboBoxTemplate_SelectionChanged">
                    <ComboBox.ItemTemplate>
                         <DataTemplate>
                             <TextBlock Text="{Binding MyItemProperty}" />
                         </DataTemplate>
                    </ComboBox.ItemTemplate>
                </ComboBox>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</StackPanel>

Expected: The selected item in the combobox is populated with MyItemType.Selection and formatted to show the MyItemProperty string. When clicking into the combobox, the items are shown with the contents of MyVmType.MyItems collection.

Actual: There is no selection when the combobox is rendered. The available items within are displayed correctly. I can confirm when actually making a selection in the cobobox, the binding property on the item are set correctly.

[pygmypenguin]

I was able to work around this by using #ElementName instead of $parent[ElementType] when binding in the data template. We've raised an issue with the Avalonia team directly as well.