WPF - Different ItemsSource for first row of DataGridComboBoxColumn-CodePudding

I have a DataGrid with several columns including a DataGridComboBoxColumn.

I'd like the ComboBox to offer a limited selection for the first row only.

<DataGridComboBoxColumn x:Name="myDataGrid"
                                    SelectedItemBinding="{Binding Direction,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" 
                                    ItemsSource="{Binding Source={StaticResource DirectionTypesCVS}}"
                                    Header="Direction" 
                                    Width="*"/>

My DirectionTypeCVS is a CollectionViewSource that returns a list of DirectionType enums, "NORTH, EAST, SOUTH, WEST". For the first row, I would like to restrict this to "NORTH" and "SOUTH".

I've tried changed the ItemsSource in the code-behind but this doesn't behave correctly. I've also tried adding a CollectionViewSource filter it doesn't appear to be being applied correctly.

What is the correct approach for this?

CodePudding user response：

I would offer you to use DataGridTemplateColumn instead of DataGridComboBoxColumn, so you get binding for the row and can find out an AlternationIndex. What you will need to do is to write a converter.

<DataGrid ItemsSource="..." AutoGenerateColumns="False" AlternationCount="2147483647">
    <DataGrid.Columns>
        <DataGridTemplateColumn >
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <ComboBox SelectedItem="{Binding Direction, UpdateSourceTrigger=PropertyChanged}">
                        <ComboBox.ItemsSource>
                            <MultiBinding Converter="{StaticResource multivalcnv}">
                                <Binding Source="{StaticResource yourStr}"/>
                                <Binding Path="AlternationIndex" RelativeSource="{RelativeSource AncestorType=DataGridRow}"/>
                            </MultiBinding>
                        </ComboBox.ItemsSource>
                    </ComboBox>
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>
    </DataGrid.Columns>
</DataGrid>

public class MultValConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        if(values != null && values.Length == 2 && values[1] is int)
            if((int)(values[1]) == 0)
            {
                return new List<string> { "Do filter the values[0]" };
            }
            else
                return values[0];
    }
    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException("It's a one way converter.");
    }
}

CodePudding user response：

You can get away from using a converter if you set the AlternationCount property of the DataGrid to int.MaxValue and use a Style with a DataTrigger that binds to the ItemsControl.AlternationIndex attached property of the parent DataGridRow:

<DataGrid ... AlternationCount="2147483647">
    <DataGrid.Columns>
        <DataGridComboBoxColumn x:Name="myDataGrid"
                                SelectedItemBinding="{Binding Direction,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" 
                                Header="Direction" 
                                Width="*">
            <DataGridComboBoxColumn.EditingElementStyle>
                <Style TargetType="ComboBox">
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding (ItemsControl.AlternationIndex),
                                        RelativeSource={RelativeSource AncestorType=DataGridRow}}" 
                                     Value="0">
                            <Setter Property="ItemsSource" Value="{Binding Source={StaticResource DirectionTypesCVSSpecial}}"/>
                        </DataTrigger>
                    </Style.Triggers>
                    <Setter Property="ItemsSource" Value="{Binding Source={StaticResource DirectionTypesCVS}}"/>
                </Style>
            </DataGridComboBoxColumn.EditingElementStyle>
        </DataGridComboBoxColumn>
        ...