Introduction
This is the WPF version of my previous articles: CRadioListBox: A ListBox with Radio Buttons (MFC Version) and RadioListBox: A ListBox with Radio Buttons (WinForms Version). As explained in those articles, RadioListBox has the same functionalities as a regular ListBox, but with a different look and feel. Anyway, the RadioListBox control offers some advantages:
- It is clearer that options are mutually exclusive with radio buttons.
- It is a good alternative to a group of radio buttons because you have to maintain just one control, less memory use.
- It inherits some useful features like scrolling, sorting, data binding, and multi-column.
- It will be easier to change options dynamically, as shown in the demo application.
- It will be easier to manage selection events, also shown in the demo application.
Using the Code
To implement RadioListBox into your project, you just need to do a few steps:
- Include RadioListBox.xaml and RadioListBox.xaml.cs into your project.
- Drop a
RadioListBox object into your XAML form, or do it by hand. An alias for the System.Windows.Controls.Custom namespace will be useful.
- Change the standard properties of the control, just like for a
ListBox.
- Use the
IsTransparent property to mimic a group of RadioButtons.
That's all! Now you can use the radio button collection as a regular ListBox. You can add items with the Items.Add() method, the ItemsSource property, or directly into XAML. Finally, query for user selection with the SelectedIndex property. No more one-by-one evaluations.
RadioListBox Internals
The RadioListBox class is derived from WPF's ListBox class with a custom ControlTemplate to remove all undesired ListBox functionalities like selected item's background. To be consistent with the radio button model, multiple selection has been disabled. The resumed XAML implementation is the following:
<ListBox x:Class="System.Windows.Controls.Custom.RadioListBox"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:s="clr-namespace:System;assembly=mscorlib" >
<ListBox.Resources>
<Style x:Key="{x:Type ListBoxItem}" TargetType="ListBoxItem">
<Setter Property="SnapsToDevicePixels" Value="true"/>
<Setter Property="OverridesDefaultStyle" Value="true"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ListBoxItem">
<RadioButton x:Name="radio" Click="ItemRadioClick">
<RadioButton.Content>
<ContentPresenter ... />
</RadioButton.Content>
</RadioButton>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ListBox.Resources>
<ListBox.Template>
<ControlTemplate>
<Border BorderThickness="0"
Padding="1,1,1,1"
Background="Transparent"
Name="theBorder"
SnapsToDevicePixels="True">
<ScrollViewer Padding="{TemplateBinding Control.Padding}"
Focusable="False">
<ItemsPresenter
SnapsToDevicePixels="{TemplateBinding UIElement.SnapsToDevicePixels}" />
</ScrollViewer>
</Border>
<ControlTemplate.Triggers ... />
</ControlTemplate>
</ListBox.Template>
</ListBox>
As the radio buttons inside the ControlTemplate don't change the selection, this has to be done manually inside the ItemRadioClick event. Here, the ItemContainerGenerator property has an important role by converting between the ListBox's items contents and the ListBoxItem presentation object. Here is a summarized C# source code:
namespace System.Windows.Controls.Custom
{
public partial class RadioListBox : ListBox
{
public RadioListBox() { ... }
public new SelectionMode SelectionMode { ... }
public bool IsTransparent { ... }
private void ItemRadioClick(object sender, RoutedEventArgs e)
{
ListBoxItem sel = (e.Source as RadioButton).TemplatedParent as ListBoxItem;
int newIndex = this.ItemContainerGenerator.IndexFromContainer(sel); ;
this.SelectedIndex = newIndex;
}
protected override void OnSelectionChanged(SelectionChangedEventArgs e)
{
base.OnSelectionChanged(e);
CheckRadioButtons(e.RemovedItems, false);
CheckRadioButtons(e.AddedItems, true);
}
private void CheckRadioButtons(System.Collections.IList radioButtons, bool isChecked)
{
foreach (object item in radioButtons)
{
ListBoxItem lbi =
this.ItemContainerGenerator.ContainerFromItem(item) as ListBoxItem;
if (lbi != null)
{
RadioButton radio = lbi.Template.FindName("radio", lbi) as RadioButton;
if (radio != null)
radio.IsChecked = isChecked;
}
}
}
}
}
History
- September 6th, 2009: First version.
