Question

This is the user control which I’m working on. The items in the first comboBox are gonna be the same in dataGridColumn GroupID.

The code to show in the first comboBox is

    <ComboBox ItemsSource="{Binding}" Name="GroupComboBox" SelectedValuePath="GroupID" DisplayMemberPath="GroupName" Grid.Column="1" Margin="5" />

    private void LoadGroups()
    {
        NorthwindDataContext dc = new NorthwindDataContext();

        var groups = (from p in dc.Group
                      select p);

        this.DataContext = groups;
    }

    private void LoadStudents()
    {
        NorthwindDataContext dc = new NorthwindDataContext();

        var students = (from p in dc.Student
                         select p);

        dataGrid1.ItemsSource = students;
    }

But in the another comboBox, don’t appear any item in it.

            <DataGridTemplateColumn Header="GroupID">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <ComboBox ItemsSource="{Binding}" SelectedValuePath="GroupID" DisplayMemberPath="GroupName" />
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>

How can I bind it?

I was thinking in put all the Groups in a list, but I’m not sure it’ll be a good way because I’d need to convert my query in a list.

UPDATE 1:

I had to remove this line:

            <DataGridComboBoxColumn Header="GroupID" ItemsSource="{Binding DataContext, RelativeSource={RelativeSource AncestorType=UserControl}}" SelectedValuePath="GroupID" DisplayMemberPath="GroupName" />

for

            <DataGridTemplateColumn Header="GroupID">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <ComboBox ItemsSource="{Binding DataContext, RelativeSource={RelativeSource AncestorType=UserControl}}" SelectedValuePath="GroupID" DisplayMemberPath="GroupName" SelectedValue="{Binding GroupID}" />
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>

Answer 1

The binding of your internal ComboBox will not work because the DataContext of that ComboBox is your Groups collection but one of the Students, this means setting the ItemsSource to {Binding} will make the Student the ItemsSource.

You can navigate up the Tree with a RelativeSource binding to a place where the inherited DataContext is still the Groups collection, e.g. if the inheritance is not blocked by setting the DataContext inbetween this will work:

{Binding DataContext, RelativeSource={RelativeSource AncestorType=DataGrid}}