WPF ComboBox - Showing something different when selecting a value - wpf

Question

What I need to accomplish is a ComboBox that shows People. When you expand the drop-down it shows FirstName and LastName, but when you select a person, the value shown at the combobox should be just the person's first name.
I have the following ItemTemplate:
<ComboBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding FirstName}" />
<TextBlock Text=" " />
<TextBlock Text="{Binding LastName}" />
</StackPanel>
</DataTemplate>
</ComboBox.ItemTemplate>
What else should I do to display only the first name when one item is selected?
Thanks!
EDIT
Changed the question slightly: What if I have the person's picture and instead of showing just the first name when a person is selected, I want to show only the picture. In other words, how can I have two separate templates - one for the drop-down and one for the selected item?

Answer 1

Here's the solution:
<ComboBox>
<ComboBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<ContentControl x:Name="content" Content="{Binding}" ContentTemplate="{StaticResource ComplexTemplate}"/>
</StackPanel>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=ComboBoxItem}}" Value="{x:Null}">
<Setter TargetName="content" Property="ContentTemplate" Value="{StaticResource SimpleTemplate}"/>
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
Basically, you create one more layer of DataTemplate here. ComboBox'es ItemTemplate always stays the same. But the content inside that template adjusts to the condition you are interested in.
The trick to discriminate dropped-down combobox items against selected-area combobox item is that selected-area is not really enclosed in ComboBoxItem object, it's part of ComboBox control itself. So FindAncestor for ComboBoxItem returns null, which we use in the trigger above.

Answer 2

I got it. I just needed to add the following to my ComboBox:
IsEditable="True" IsReadOnly="True" TextSearch.TextPath="FirstName"

Answer 3

Put a Trigger on the DataTemplate. The trigger should check the IsSelected property (the DataTemplate will need a TargetType set for this to work). If it is selected, you can set the Visibility of your TextBlocks to Collapsed, and set the Visibility of the Image to Visible. Then do the opposite for the case that it is not selected.

Answer 4

Another option is to use ItemTemplateSelector instead of ItemTemplate. I've been using it the following way.
ComboBoxItemTemplateSelector derives from DataTemplateSelector and has two attached properties, SelectedTemplate and DropDownTemplate. Then we set the DataTemplates from Xaml like this
<ComboBox ItemsSource="{Binding Persons}"
ItemTemplateSelector="{StaticResource ComboBoxItemTemplateSelector}">
<ts:ComboBoxItemTemplateSelector.SelectedTemplate>
<DataTemplate>
<TextBlock Text="{Binding FirstName}" />
</DataTemplate>
</ts:ComboBoxItemTemplateSelector.SelectedTemplate>
<ts:ComboBoxItemTemplateSelector.DropDownTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding FirstName}" />
<TextBlock Text=" " />
<TextBlock Text="{Binding LastName}" />
</StackPanel>
</DataTemplate>
</ts:ComboBoxItemTemplateSelector.DropDownTemplate>
</ComboBox>
In SelectTemplate we check if the current container is wrapped in a ComboBoxItem and if it is, we return the DropDownTemplate. Otherwise we return SelectedTemplate.
public class ComboBoxItemTemplateChooser : DataTemplateSelector
{
#region SelectedTemplate..
#region DropDownTemplate..
public override DataTemplate SelectTemplate(object item,
DependencyObject container)
{
ComboBox parentComboBox = null;
ComboBoxItem comboBoxItem = container.GetVisualParent<ComboBoxItem>();
if (comboBoxItem == null)
{
parentComboBox = container.GetVisualParent<ComboBox>();
return ComboBoxItemTemplateChooser.GetSelectedTemplate(parentComboBox);
}
parentComboBox = ComboBox.ItemsControlFromItemContainer(comboBoxItem) as ComboBox;
return ComboBoxItemTemplateChooser.GetDropDownTemplate(parentComboBox);
}
}
A small demo project that uses this can be downloaded here: ComboBoxItemTemplateDemo.zip
I also made a short blog-post about this here: Different ComboBox ItemTemplate for dropdown. It also shows the other obvious way of doing the same thing but with properties instead of attached properties in ComboBoxItemTemplateSelector.
Oh, and GetVisualParent. Everyone seems to have their own implementations of this but anyway, here's the one I'm using
public static class DependencyObjectExtensions
{
public static T GetVisualParent<T>(this DependencyObject child) where T : Visual
{
while ((child != null) && !(child is T))
{
child = VisualTreeHelper.GetParent(child);
}
return child as T;
}
}

Answer 5

I used next approach
<UserControl.Resources>
<DataTemplate x:Key="SelectedItemTemplate" DataType="{x:Type statusBar:OffsetItem}">
<TextBlock Text="{Binding Path=ShortName}" />
</DataTemplate>
</UserControl.Resources>
<StackPanel Orientation="Horizontal">
<ComboBox DisplayMemberPath="FullName"
ItemsSource="{Binding Path=Offsets}"
behaviors:SelectedItemTemplateBehavior.SelectedItemDataTemplate="{StaticResource SelectedItemTemplate}"
SelectedItem="{Binding Path=Selected}" />
<TextBlock Text="User Time" />
<TextBlock Text="" />
</StackPanel>
And the behavior
public static class SelectedItemTemplateBehavior
{
public static readonly DependencyProperty SelectedItemDataTemplateProperty =
DependencyProperty.RegisterAttached("SelectedItemDataTemplate", typeof(DataTemplate), typeof(SelectedItemTemplateBehavior), new PropertyMetadata(default(DataTemplate), PropertyChangedCallback));
public static void SetSelectedItemDataTemplate(this UIElement element, DataTemplate value)
{
element.SetValue(SelectedItemDataTemplateProperty, value);
}
public static DataTemplate GetSelectedItemDataTemplate(this ComboBox element)
{
return (DataTemplate)element.GetValue(SelectedItemDataTemplateProperty);
}
private static void PropertyChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var uiElement = d as ComboBox;
if (e.Property == SelectedItemDataTemplateProperty && uiElement != null)
{
uiElement.Loaded -= UiElementLoaded;
UpdateSelectionTemplate(uiElement);
uiElement.Loaded += UiElementLoaded;
}
}
static void UiElementLoaded(object sender, RoutedEventArgs e)
{
UpdateSelectionTemplate((ComboBox)sender);
}
private static void UpdateSelectionTemplate(ComboBox uiElement)
{
var contentPresenter = GetChildOfType<ContentPresenter>(uiElement);
if (contentPresenter == null)
return;
var template = uiElement.GetSelectedItemDataTemplate();
contentPresenter.ContentTemplate = template;
}
public static T GetChildOfType<T>(DependencyObject depObj)
where T : DependencyObject
{
if (depObj == null) return null;
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++)
{
var child = VisualTreeHelper.GetChild(depObj, i);
var result = (child as T) ?? GetChildOfType<T>(child);
if (result != null) return result;
}
return null;
}
}
worked like a charm. Don't like pretty much Loaded event here but you can fix it if you want