How to disable a specific DataGid Cell of a new row

Question

I have a simple DataGrid with two columns like

<DataGrid ItemsSource="{Binding Commands}" CanUserAddRows="True" AutoGenerateColumns="False">
    <DataGrid.Columns>
        <DataGridTextColumn Header="Value" Binding="{Binding Value}"/>
        <DataGridTemplateColumn Header="Command">
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <ComboBox ItemsSource="{Binding ComboItems}" SelectedValue="{Binding SelectedItem}">
                        <ComboBox.ItemTemplate>
                            <DataTemplate>
                                <TextBlock Text="{Binding Converter={StaticResource ItemConverter}}"/>
                            </DataTemplate>
                        </ComboBox.ItemTemplate>
                    </ComboBox>
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>
    </DataGrid.Columns>
</DataGrid>

My goal is to disable the cell with the ComboBox of the new row. The following picture shows my DataGrid (bound to a ObservableCollection of two items) with the column to disable marked.

I tried already to use a converter to disable the ComboBox

IsEnabled="{Binding Value, Converter={StaticResource DisableConverter}}"

but the converter don't get's called until I entered a value inside the first column.

Hope anybody can help me!

Answer 1

You could apply the following Style to the ComboBox:

<ComboBox ItemsSource="{Binding ComboItems}" SelectedValue="{Binding SelectedItem}">
    <ComboBox.Style>
        <Style TargetType="ComboBox">
            <Style.Triggers>
                <DataTrigger Binding="{Binding Path=DataContext,RelativeSource={RelativeSource AncestorType=DataGridRow}}" 
                                                         Value="{x:Static CollectionView.NewItemPlaceholder}">
                    <Setter Property="IsEnabled" Value="False" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </ComboBox.Style>
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding Converter={StaticResource ItemConverter}}"/>
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>