#1,012 – Using a Different Data Template for the Face of a ComboBox

February 19, 2014 1 Comment

When you define a data template to use as the item template for a ComboBox, this item template is used to render each item in the dropdown list when it appears.  The same item template is used to display the currently selected item on the face of the ComboBox.

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You can define a different template for the face of the ComboBox using a DataTemplateSelector.  You start by defining a data template selector that allows setting one of two templates and can determine whether the parent of the current item is the ComboBox itself (face of button) or a ComboBoxItem (dropdown).

    public class ComboBoxItemTemplateSelector : DataTemplateSelector
    {
        // Can set both templates from XAML
        public DataTemplate SelectedItemTemplate { get; set; }
        public DataTemplate ItemTemplate { get; set; }

        public override DataTemplate SelectTemplate(object item, DependencyObject container)
        {
            bool selected = false;

            // container is the ContentPresenter
            FrameworkElement fe = container as FrameworkElement;
            if (fe != null)
            {
                DependencyObject parent = fe.TemplatedParent;
                if (parent != null)
                {
                    ComboBox cbo = parent as ComboBox;
                    if (cbo != null)
                        selected = true;
                }
            }

            if (selected)
                return SelectedItemTemplate;
            else
                return ItemTemplate;
        }
    }

You can now define two different templates in your XAML.

        <ComboBox ItemsSource="{Binding ActorList}" Margin="20"
                  SelectedItem="{Binding SelectedActor}">
            <ComboBox.ItemTemplateSelector>
                <local:ComboBoxItemTemplateSelector>
                    <local:ComboBoxItemTemplateSelector.ItemTemplate>
                        <DataTemplate>
                            <StackPanel Orientation="Horizontal">
                                <Image Source="{Binding Image}" Height="100"/>
                                <StackPanel Margin="10,0">
                                    <TextBlock Text="{Binding FullName}" FontWeight="Bold" />
                                    <TextBlock Text="{Binding Dates}"/>
                                    <TextBlock Text="{Binding KnownFor}" FontStyle="Italic"/>
                                </StackPanel>
                            </StackPanel>
                        </DataTemplate>
                    </local:ComboBoxItemTemplateSelector.ItemTemplate>
                    <local:ComboBoxItemTemplateSelector.SelectedItemTemplate>
                        <DataTemplate>
                            <StackPanel Orientation="Horizontal">
                                <Image Source="{Binding Image}" Height="40" Margin="5,0"/>
                                <TextBlock Text="{Binding FullName}"/>
                            </StackPanel>
                        </DataTemplate>
                    </local:ComboBoxItemTemplateSelector.SelectedItemTemplate>
                </local:ComboBoxItemTemplateSelector>
            </ComboBox.ItemTemplateSelector>
        </ComboBox>

We now have a different layout on the face of the ComboBox, showing the currently selected item.

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#1,011 – ComboBox Data Binding Basics, Part III

February 18, 2014 5 Comments

To display the items in a ComboBox using something more than a simple string, you set the ItemTemplate of the ComboBox to define the layout of each item.  When you set the ItemTemplate, you don’t set the DisplayMemberPath property.  DisplayMemberPath defines the template for each item in the ComboBox to be a TextBlock that displays a single string.

Below, we set an item template for a ComboBox that binds to a collection of Actor objects so that we display an image and some information about the actor, for each item.

        <ComboBox ItemsSource="{Binding ActorList}" Margin="20"
                  SelectedItem="{Binding SelectedActor}">
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <Image Source="{Binding Image}" Height="100"/>
                        <StackPanel Margin="10,0">
                            <TextBlock Text="{Binding FullName}" FontWeight="Bold" />
                            <TextBlock Text="{Binding Dates}"/>
                            <TextBlock Text="{Binding KnownFor}" FontStyle="Italic"/>
                        </StackPanel>
                    </StackPanel>
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>
        <Label Content="{Binding SelectedActor.NameAndDates}"/>

As we select an item, notice that the ComboBox changes size, so that the surface can show the entire item.

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