Add placeholder DataGrid item after ComboBox selection

Question

I have a WPF DataGrid with a possibility of add new rows (CanUserAddRows="True"). One of my columns is a ComboBox. With the following code I can bind data to this ComboBox:

<DataGridTemplateColumn Header="Validator" MinWidth="150">
   <DataGridTemplateColumn.CellTemplate>
      <DataTemplate>
         <ComboBox ItemsSource="{Binding DataContext.ValidatorVariables, RelativeSource={RelativeSource FindAncestor, AncestorType=Window}, UpdateSourceTrigger=PropertyChanged}"
                      SelectedItem="{Binding SelectedValidatorVariable, UpdateSourceTrigger=PropertyChanged}"
                      IsEnabled="{Binding HasValidator, UpdateSourceTrigger=PropertyChanged}">

If I select a ComboBox item first in a placeholder row, then new item won't be created from this placeholder row. Placeholder row will be added to the item source only if I enter edit mode in a Text column. CheckBox column does not work either, only Text column.

This causes a sideffect:

1. select ComboBox item
2. enter edit mode in a Text column

Result: previously selected ComboBox item is cleared

Is there any solution for this scenario?

Answer 1

Any input control, such as for example a ComboBox, is supposed to be put in the CellEditingTemplate. The CellTemplate should contain a TextBlock that displays the currently selected value:

<DataGridTemplateColumn Header="Validator" MinWidth="150">
    <DataGridTemplateColumn.CellTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding SelectedValidatorVariable}" />
        </DataTemplate>
    </DataGridTemplateColumn.CellTemplate>
    <DataGridTemplateColumn.CellEditingTemplate>
        <DataTemplate>
            <ComboBox ... />
        </DataTemplate>
</DataGridTemplateColumn>