DataGrid does not refresh if source updated outside view

Describe the bug In Avalonia 0.11.0-Preview4 when updating (add or delete) the Items of a DataGrid when the view is not displayed (in another TabItem for example) the DataGrid doesn’t get refreshed.

The issue doesn’t happen in 0.18.0

To Reproduce Steps to reproduce the behavior:

public class TestModel : ViewModelBase
{
    public string Name { get; }

    public TestModel( string name )
    {
        Name = name;
    }
}

public class MainWindowViewModel : ViewModelBase
{
    private ObservableCollection<TestModel> _items = new();
    public ObservableCollection<TestModel> Items
    {
        get => _items;
        set => this.RaiseAndSetIfChanged( ref _items, value );
    }

    public void Clear()
    {
        Items.Clear();
    }

    public void AddItems()
    {
        for ( int ii = 0; ii < 10; ii++ )
        {
            Items.Add( new TestModel( $"Item: {ii}" ) );
        }
    }
}

    <Window.DataTemplates>
        <DataTemplate DataType="vm:TestModel">
            <TextBlock Text="{Binding Name}" />
        </DataTemplate>
    </Window.DataTemplates>

    <DockPanel>
        <StackPanel DockPanel.Dock="Top" Orientation="Horizontal">
            <Button Command="{Binding Clear}" Content="Clear" />
            <Button Command="{Binding AddItems}" Content="Add Items" />
        </StackPanel>

        <TabControl>
            <TabItem Header="A">
                <Grid ColumnDefinitions="*,*">
                    <DataGrid Grid.Column="0" Items="{Binding Items}">
                        <DataGrid.Columns>
                            <DataGridTextColumn x:DataType="vm:TestModel" Header="Name" Binding="{Binding Name}" />
                        </DataGrid.Columns>
                    </DataGrid>

                    <ListBox Grid.Column="1" Items="{Binding Items}" />
                </Grid>
            </TabItem>

            <TabItem Header="B">
            </TabItem>
        </TabControl>
    </DockPanel>

1. Click the Add Item Button
2. Switch to Tab “B”
3. Click the Clear Button
4. Switch to Tab “A”
5. The Items in the DataGrid have not been cleared (the ListBox is here for reference).

Same issue when clicking Add Items in the “B” Tab, the added Items are not displayed in the DataGrid.

Expected behavior

The removed items should not be shown.

Desktop:

• Windows 10 Pro 22H2
• Tested with Version 0.11.0-Preview1 and Version 0.11.0-Preview4.

[alexandrehtrb]

I just faced this issue, here is my temporary solution: switch to the tab that shows the DataGrid, update its ItemsSource, then switch back to the tab that was visible before. This makes the DataGrid view to be updated.

[almightyju]

This is caused by this code in the DataGrid: https://github.com/AvaloniaUI/Avalonia/blob/7580b704dff69b648b1fe73ebd7071b0c20bd4f0/src/Avalonia.Controls.DataGrid/DataGrid.cs#L2110-L2118

Simply not unwiring events seems to work but I don’t know what the resolution should be while keeping the intended behaviour.

Looking at the commit https://github.com/AvaloniaUI/Avalonia/commit/bbf3099a8f9f482f851f6cfe497f22c8ca95bbcf indicates the problem was a ViewModel/Collection keeping the DataGrid from being garbage collected, but that strikes me as an intended thing, if the ViewModel isn’t being released then why would you expect the view for it to be released.

On second thought perhaps simply calling InitializeElements(false /*recycleRows*/); during OnAttachedToVisualTree is called would be the best approach