Set GroupStyle inside style on xaml - wpf

Question

I'm Trying to set default style for ContexMenu and I want to set default GroupStyle to ContexMenu inside the style. Something like this:
<Setter Property="ItemsControl.GroupStyle">
<Setter.Value>
<GroupStyle>
<...>
</GroupStyle>
</Setter.Value>
</Setter>
But the compiler say error: it can't find GroupStyle on ItemsControl.
However ,in code I can do simply:
ContextMenu contextMenu;
contextMenu.GroupStyle.Add(someSavedStyle);
How can I achieve this in xaml?
Thanks in advance!

Answer 1

You can use an attached property to simplify adding group styles:
<Style TargetType="MenuItem">
<Setter Property="b:GroupStyleEx.Append">
<Setter.Value>
<GroupStyle .. />
</Setter.Value>
</Setter>
<!-- you can add as many as you like... -->
<Setter Property="b:GroupStyleEx.Append">
<Setter.Value>
<!-- second group style -->
<GroupStyle .. />
</Setter.Value>
</Setter>
</Style>
Here's the code for the attached property:
using System;
using System.Windows;
using System.Windows.Controls;
namespace Util
{
public static class GroupStyleEx
{
public static readonly DependencyProperty AppendProperty
= DependencyProperty.RegisterAttached("Append", typeof (GroupStyle), typeof (GroupStyleEx),
new PropertyMetadata(AppendChanged));
public static GroupStyle GetAppend(DependencyObject obj)
{
return (GroupStyle) obj.GetValue(AppendProperty);
}
public static void SetAppend(DependencyObject obj, GroupStyle style)
{
obj.SetValue(AppendProperty, style);
}
private static void AppendChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var itemsControl = d as ItemsControl;
if (itemsControl == null)
throw new InvalidOperationException("Can only add GroupStyle to ItemsControl");
var #new = e.NewValue as GroupStyle;
if (#new != null)
itemsControl.GroupStyle.Add(#new);
}
}
}

Answer 2

The way I resolved this was create a new control that inherits from ListBox control that adds a bindable DefaultGroupStyle:
public class MyListBox : ListBox
{
public GroupStyle DefaultGroupStyle
{
get { return (GroupStyle)GetValue(DefaultGroupStyleProperty); }
set { SetValue(DefaultGroupStyleProperty, value); }
}
// Using a DependencyProperty as the backing store for DefaultGroupStyle. This enables animation, styling, binding, etc...
public static readonly DependencyProperty DefaultGroupStyleProperty =
DependencyProperty.Register("DefaultGroupStyle", typeof(GroupStyle), typeof(MyListBox), new UIPropertyMetadata(null, DefaultGroupStyleChanged));
private static void DefaultGroupStyleChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
{
((MyListBox)o).SetDefaultGroupStyle(e.NewValue as GroupStyle);
}
private void SetDefaultGroupStyle(GroupStyle defaultStyle)
{
if (defaultStyle == null)
{
return;
}
if (this.GroupStyle.Count == 0)
{
this.GroupStyle.Add(defaultStyle);
}
}
}

Answer 3

Actually, with some extra work it can be done:
Instead of setting the template of ContexMenu to ItemsPresenter, you can set it to control that will fit you data. In this case , you can set it to Menu. Just like this:
<Style TargetType="ContextMenu">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ContextMenu">
<Border>
<Menu ItemsSource="{TemplateBinding ItemsSource}">
<Menu.GroupStyle>
<GroupStyle>
<GroupStyle.ContainerStyle>
<Style TargetType="{x:Type GroupItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type GroupItem}">
<StackPanel>
<Border Background="Black">
<ItemsPresenter/>
</Border>
</StackPanel>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</GroupStyle.ContainerStyle>
</GroupStyle>
</Menu.GroupStyle>
<Menu.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel></StackPanel>
</ItemsPanelTemplate>
</Menu.ItemsPanel>
</Menu>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
Now, though the GroupStyle is readonly, we can set it through PropertyElement :-)
In order to get exactly the feel of MenuItem of ContexMenu you can adjust the style of MenuItem