Column virtualization for DataGrid initially hides column headers

[cbra-caa]

My problem is that when I draw a DataGrid without any initial rows (a search waiting for user input) the column headers are not drawn when I run with column virtualization.

After an initial set of rows has been added the headers display as expected, even if the rows are cleared again.

• All columns in my DataGrid have a set width, so they are renderable.
• I have tried flipping EnableColumnVirtualization based on when DataGrid.Items is populated, but the DataGridCellsPanel responsible for the headers are redrawn when it is flipped which leads to an annoying jump.
• I have tried different approaches of forcing measure/arrange on the DataGridColumnHeadersPresenter but it seems to ignore them an await a certain flag I cant make out.

That the headers are stable after some rows have been initialized suggests to me that it should be possible. Does anyone know if this can be forced somehow?

[miloush]

Do you have a repro project for others to try?

[miloush]

drag and drop a zip file here in the text box :)

[cbra-caa]

The test project here should be run, as is, new items can be added and removed through the contextmenu.

In recreating the problem I realized that it is confined to the case where you apply a GroupStyle to the DataGrid. Currently I am tinkering with a solution where GroupStyles are added in a new DependencyProperty which acts as a placeholder until the DataGrid is populated with rows.

DataGridColumnVirtualization.zip

[cbra-caa]

This seems to be working for me:

    private List<GroupStyle> DeferredGroupStyles { get; set; }

    public override void OnApplyTemplate()
    {
      base.OnApplyTemplate();

      if (GroupStyle.Any() && Items.Count == 0)
      {
        DeferredGroupStyles = GroupStyle.ToList();
        GroupStyle.Clear();
      }
    }

    protected override void OnItemsChanged(NotifyCollectionChangedEventArgs e)
    {
      base.OnItemsChanged(e);

      if (DeferredGroupStyles != null && Items.Count != 0)
      {
        foreach (var item in DeferredGroupStyles)
        {
          GroupStyle.Add(item);
        }

        DeferredGroupStyles = null;
      }
    }

[miloush]

Hm, I can see the issue and it does feel like a bug I have to say.

[cbra-caa]

I can convert it to an issue if you would like 👍