Opening a ContextMenu from a button click - wpf

Question

I'm trying to create a button that displays content in a popup when it is clicked. So I came up with something simple like this :
public class DropdownButton : Button
{
public object DropdownContent
{
get { return (object)GetValue(DropdownContentProperty); }
set { SetValue(DropdownContentProperty, value); }
}
public static readonly DependencyProperty DropdownContentProperty =
DependencyProperty.Register("DropdownContent", typeof(object), typeof(DropdownButton), new PropertyMetadata(null));
protected override void OnClick()
{
base.OnClick();
if(DropdownContent != null)
{
if(DropdownContent is ContextMenu)
{
ContextMenu = (ContextMenu)DropdownContent;
ContextMenu.IsOpen = true;
}
else
{
// launch a popup
}
}
}
}
and am using it like this :
public partial class MainWindow : Window
{
public string A { get { return "A"; } }
public string B { get { return "B"; } }
public MainWindow()
{
DataContext = this;
InitializeComponent();
}
}
<Window x:Class="WpfApplication45.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:l="clr-namespace:WpfApplication45"
Title="MainWindow"
WindowStartupLocation="CenterScreen">
<Window.Resources>
<ContextMenu x:Key="sharedMenu">
<MenuItem Header="{Binding}" />
</ContextMenu>
</Window.Resources>
<StackPanel>
<UniformGrid Columns="2"
DataContext="{Binding A}">
<TextBlock Text="{Binding}"
Background="#CCC"
ContextMenu="{StaticResource sharedMenu}"/>
<l:DropdownButton DropdownContent="{StaticResource sharedMenu}" />
</UniformGrid>
<UniformGrid Columns="2"
DataContext="{Binding B}">
<TextBlock Text="{Binding}"
Background="#CCC"
ContextMenu="{StaticResource sharedMenu}"/>
<l:DropdownButton DropdownContent="{StaticResource sharedMenu}" />
</UniformGrid>
</StackPanel>
But it isn't behaving as expected. If you try clicking a button, the ContextMenu pops up but without having it's DataContext set.
If I manually set the DataContext like this :
ContextMenu = (ContextMenu)DropdownContent;
ContextMenu.DataContext = DataContext;
ContextMenu.IsOpen = true;
it breaks the binding on the TextBlocks ContextMenu

Answer 1

To be perfectly honest, I don't know why this works, but if I apply the following change :
protected override void OnClick()
{
base.OnClick();
if (DropdownContent != null)
{
if (DropdownContent is ContextMenu)
{
ContextMenu = (ContextMenu)DropdownContent;
ContextMenu.PlacementTarget = this;
ContextMenu.IsOpen = true;
}
else
{
// launch a popup
}
}
}
As well as disable Menu animations :
<Application.Resources>
<PopupAnimation x:Key="{x:Static SystemParameters.MenuPopupAnimationKey}">None</PopupAnimation>
</Application.Resources>
Things work ...