DataGrid 'EditItem' is not allowed for this view when dragging multiple items

Instead of using a struct use a class instead.

UPDATED ANSWER: Try adding your MyData instances to a List then assigning that list to the DataGrid.ItemsSource

I got this issue when assigning ItemsSource to IEnumerable<T>.

I fixed it by converting the IEnumberable<T> to a List<T> and then assigning that to ItemsSource.

I'm not sure why using IEnumerable caused that issue, but this change fixed it for me.