Wpf multiple combobox binding to one property

Question

I am having a data grid, one of its cells is a combo box like:

<DataGrid x:Name="Applications"  RowStyle="{StaticResource CollapsedRow}" AutoGenerateColumns="false" CanUserAddRows="false" ItemsSource="{Binding Applications}">

<DataGrid.Columns>
   <DataGridTemplateColumn>
     <DataGridTemplateColumn.CellTemplate>
      <DataTemplate>
         <Button Content='&#709;' FontSize="9" Name="ExpanderButton" Click="OnGroupChange" />
      </DataTemplate>
 </DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>

 <DataGridTextColumn Width="181" Header="Name" Binding="{Binding Name, Mode=OneWay}" />

</DataGrid.Columns>

<DataGrid.RowDetailsTemplate>
 <DataTemplate>
  <ComboBox ItemsSource="{Binding Path=DataContext.Cabins, 
       RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DataGrid}}}" 
       SelectedValuePath="Id" IsSynchronizedWithCurrentItem="True"
       SelectedValue="{Binding Path=DataContext.SelectedCabin,
       RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DataGrid}}, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
       mah:TextBoxHelper.Watermark="{Binding Path=DataContext.CabinsWatermark, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DataGrid}}}"
                                                                      Height="2" Width="300" Margin="10 5 10 10" HorizontalAlignment="Left">
 <ComboBox.ItemTemplate>
    <DataTemplate>
      <TextBlock Text="{Binding Converter={StaticResource GuidConverter}}"/>
    </DataTemplate>
</ComboBox.ItemTemplate> 
</ComboBox>
 </DataTemplate>
</DataGrid.RowDetailsTemplate>

</DataGrid>

And as you see in each row there ia a combo box in detail row (expanded row using button), each combo box is binded to one property:

 private Guid? selectedCabin;
    public override  Guid? SelectedCabin
    {
        get => selectedCabin;
        set
        {
            selectedCabin = value;
            if (value.HasValue)
            {
                Console.WriteLine(value);
            }

            OnPropertyChanged();
        }

Now problem is when i select item in combo box i am getting not single value but couple of them (I suppose there are all values from one combo box I made a selection on), to make sure i double checked with test code behind:

     private void ComboBox_OnSelectCabinChanged(object sender, RoutedEventArgs e)
    {
        var combo = (ComboBox)sender;

        if (combo != null && combo.IsDropDownOpen)
        {
            ((ApplicationsViewModel)DataContext).SelectedCabin = (Guid?)sender;
            combo.IsDropDownOpen = false;
        }
    }

And I am getting here and combo box item list and casting exception. What could be the root cause of this and is there a way to bind multiple combo box values to one property, so is i select one it will override another.

Answer 1

It seems like you are binding the SelectedValue of all row details ComboBoxes to the same source property. And you can't cast the sender argument to a Guid? . Try to cast the SelecteedValue property of the ComboBox :

SelectedCabin = (Guid?)combo.SelectedValue;

If you don't want to handle the SelectionChanged event in the view, you could use an interaction trigger that executes a command that sets the source property. Please refer to this blog post for more information about this.