DataGrid DataGridComboBoxColumn lose its value after collapsing

Question

I have a GridView whith DataGridComboBoxColumn, it works fine the first time, but when set the column visibility to collapsed, and then return the visibility to visible again, the column lose its value. but the property which is bounded to it still has the correct value.

when refresh the DataContext all the values gets binded correctly.

I add a test Converter, and noticed that when collapsing the column, the call back method is fired, and the value is null.

<DataGridComboBoxColumn SelectedValueBinding="{Binding DbId}"
                        DisplayMemberPath="Name"
                        SelectedValuePath="Id"
                        Visibility="Visible">
    <DataGridComboBoxColumn.ElementStyle>
        <Style TargetType="ComboBox">
            <Setter Property="ItemsSource" Value="{Binding TestList}"/>
        </Style>
    </DataGridComboBoxColumn.ElementStyle>
    <DataGridComboBoxColumn.EditingElementStyle>
        <Style TargetType="ComboBox">
            <Setter Property="ItemsSource" Value="{Binding TestList}"/>
        </Style>
    </DataGridComboBoxColumn.EditingElementStyle>
</DataGridComboBoxColumn>

Answer 1

I can reproduce your issue. You could work around it by handling the Loaded event for the ComboBox in the CellTemplate and re-set the SelectedValue property:

<DataGridComboBoxColumn.ElementStyle>
    <Style TargetType="ComboBox">
        <Setter Property="ItemsSource" Value="{Binding TestList}"/>
        <EventSetter Event="Loaded" Handler="OnLoaded" />
    </Style>
</DataGridComboBoxColumn.ElementStyle>

---

private void OnLoaded(object sender, RoutedEventArgs e)
{
    ComboBox cmb = sender as ComboBox;
    dynamic dataObject = cmb.DataContext;
    cmb.SelectedValue = dataObject.DbId;
}

Another solution would be to replace the DataGridComboBoxColumn with a DataGridTemplateColumn. You then want to bind the SelectedItem property of the ComboBox to a Db property of your data object to be able to display the Name property of the Db object in the CellTemplate.