StringFormat does not apply in MultiSelectionComboBox selection

[ExLuzZziVo]

Hi,

There is an issue with MultiSelectionComboBox: if I want to apply ItemStringFormat, it is only gets applied on items in dropdown, but not on items in combobox's total text field. Please, take a look at example screenshot

Steps to reproduce:

1. Create ViewModel

public class ViewModel: INotifyPropertyChanged
{

        private ObservableCollection<DateTime> _dateTimes = new ObservableCollection<DateTime>() {DateTime.Now, new DateTime(2019, 4, 23)};
        public ObservableCollection<DateTime> DateTimes
        {
            get => _dateTimes;
            set
            {
                _dateTimes = value;
                OnPropertyChanged(nameof(DateTimes));
            }
        }
        
        [field: NonSerialized] public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
}

2. Add MultiSelectionComboBox control to XAML and bind it to ViewModel

<timsWpfControls:MultiSelectionComboBox SelectionMode="Multiple" ItemsSource="{Binding DateTimes}" ItemStringFormat="{}{0:D}"/>

3. Select all items and see the result

[timunie]

Hi @ExLuzZziVo

Thank you for posting this 🙏 . I am transferring this control to MahApps (see MahApps/MahApps.Metro#4006 ) and will address this issue there.

I think for now you should be able to overcome this by using a custom SelectedItemTemplate

Here is the original:

TimsWpfControls/TimsWpfControls/TimsWpfControls/Themes/MultiSelectionComboBox.xaml

Lines 16 to 54 in 0ff6be0

	<!--#region DataTemplates-->
	<DataTemplate x:Key="Tims.DataTemplates.MultiSelectionComboBox.Removeable">
	<Grid>
	<Border Margin="2"
	Background="{DynamicResource MahApps.Brushes.Gray8}"
	CornerRadius="{Binding RelativeSource={RelativeSource Mode=Self}, Path=ActualHeight, Converter={StaticResource MahApps.Converters.SizeToCornerRadius}}"
	IsHitTestVisible="False" />
	<StackPanel Margin="7,2,2,2" Orientation="Horizontal">
	<ContentControl Margin="0"
	VerticalAlignment="Center"
	Content="{Binding}"
	IsHitTestVisible="False" />
	<Button Width="10"
	Height="10"
	Margin="5,2,2,2"
	VerticalAlignment="Center"
	mah:ControlsHelper.CornerRadius="5"
	Command="ctrls:MultiSelectionComboBox.RemoveItemCommand"
	CommandParameter="{Binding}"
	IsHitTestVisible="True">
	<Button.Style>
	<Style BasedOn="{StaticResource MahApps.Styles.Button.Chromeless}" TargetType="Button">
	<Style.Triggers>
	<Trigger Property="IsMouseOver" Value="True">
	<Setter Property="Foreground" Value="{DynamicResource MahApps.Brushes.Accent2}" />
	</Trigger>
	<Trigger Property="IsPressed" Value="True">
	<Setter Property="Foreground" Value="{DynamicResource MahApps.Brushes.Highlight}" />
	</Trigger>
	</Style.Triggers>
	</Style>
	</Button.Style>
	<Path Data="M10,1.6c-4.639,0-8.4,3.761-8.4,8.4c0,4.639,3.761,8.4,8.4,8.4s8.4-3.761,8.4-8.4C18.4,5.361,14.639,1.6,10,1.6z M14.789,13.061l-1.729,1.729L10,11.729l-3.061,3.06l-1.729-1.729L8.272,10L5.211,6.939L6.94,5.211L10,8.271l3.061-3.061 l1.729,1.729L11.728,10L14.789,13.061z"
	Fill="{Binding RelativeSource={RelativeSource AncestorType=Button}, Path=Foreground}"
	Stretch="Uniform" />
	</Button>
	</StackPanel>
	</Grid>
	</DataTemplate>

Happy coding and a happy new year
Tim

[ExLuzZziVo]

I have found a solution. In GetSelectedItemsText method of MultiSelectionComboBox.cs I have used this code and it works:

            IEnumerable<object> values;

            if (ReadLocalValue(DisplayMemberPathProperty) != DependencyProperty.UnsetValue && !string.IsNullOrEmpty(DisplayMemberPath))
            {
                values = ((IEnumerable<object>)SelectedItems)?.Select(o => BindingHelper.Eval(o, DisplayMemberPath ?? string.Empty));
            }
            else
            {
                values = (IEnumerable<object>)SelectedItems;
            }

            if (values != null && ReadLocalValue(ItemStringFormatProperty) != DependencyProperty.UnsetValue &&
                !string.IsNullOrEmpty(ItemStringFormat))
            {
                values = values.Select(o => string.Format(ItemStringFormat, o));
            }

Happy holidays!

[timunie]

@ExLuzZziVo thank you for providing your solution. I think I found an even better way, but it will not be implemented here. It will be available in MahApps soon (no due date right now).

Happy new year and happy coding
Tim

[ExLuzZziVo]

@timunie Thank you. I will close the issue