Close combobox after n seconds - wpf

Question

I have a combobox that stays open if the user does not make a selection. I'd like to use a trigger to close the combobox after 2 seconds. Here is a portion of my combobox style that includes my failed eventtrigger attempt at accomplishing this:
<Style x:Key="ComboBoxStyle" TargetType="{x:Type ComboBox}">
<Setter Property="FontFamily" Value="Bryant"/>
<Setter Property="FontSize" Value="18px"/>
<Setter Property="FontWeight" Value="Bold"/>
<Setter Property="FocusVisualStyle" Value="{StaticResource ComboBoxFocusVisual}"/>
<Setter Property="Foreground" Value="#FF000000"/>
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"/>
<Setter Property="Padding" Value="4,3"/>
<Setter Property="Margin" Value="5"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBox}">
<Grid x:Name="MainGrid" SnapsToDevicePixels="true">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="0*"/>
<ColumnDefinition/>
<ColumnDefinition MinWidth="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}" Width="0"/>
</Grid.ColumnDefinitions>
<Popup Margin="1" x:Name="PART_Popup" AllowsTransparency="true" StaysOpen="False" IsOpen="{Binding IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}" Placement="Bottom" PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}" Grid.ColumnSpan="2" Grid.Column="1">
<Border x:Name="DropDownBorder" Background="{DynamicResource GrayBG}" MaxHeight="{TemplateBinding MaxDropDownHeight}" MinWidth="{Binding ActualWidth, ElementName=MainGrid}" BorderBrush="{StaticResource GrayBGBorder}" BorderThickness="2,0,2,2" CornerRadius="0,0,4,4" Width="{Binding ActualWidth, ElementName=DropWidth}">
<ScrollViewer CanContentScroll="true" Template="{DynamicResource NeeboScrollViewer}">
<ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" KeyboardNavigation.DirectionalNavigation="Contained"/>
</ScrollViewer>
</Border>
</Popup>
<ToggleButton x:Name="DropWidth" Style="{StaticResource ComboBoxReadonlyToggleButton}" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" Grid.ColumnSpan="2" IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Grid.Column="1"/>
<ContentPresenter HorizontalAlignment="Left" Margin="35,0,0,0" VerticalAlignment="Center" IsHitTestVisible="false" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" Content="{TemplateBinding SelectionBoxItem}" ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}" Grid.Column="1"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasItems" Value="false">
<Setter Property="Height" TargetName="DropDownBorder" Value="95"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
<Setter Property="Background" Value="#FFF4F4F4"/>
</Trigger>
<Trigger Property="IsGrouping" Value="true">
<Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
</Trigger>
<EventTrigger RoutedEvent="(Popup.Opened)" SourceName="PART_Popup" >
<BeginStoryboard>
<Storyboard>
<BooleanAnimationUsingKeyFrames Storyboard.TargetName="PART_Popup" Storyboard.TargetProperty="(Popup.IsOpen)">
<DiscreteBooleanKeyFrame KeyTime="00:00:03" Value="False"/>
</BooleanAnimationUsingKeyFrames>
</Storyboard>
</BeginStoryboard>
</EventTrigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
Any suggestions on how to accomplish this?

Answer 1

I can't think of a way doing this without implement attached behavior that will subscribe the opened event and wait 2 seconds to close it if not closed already.
If you don't know what is attached behavior just google it.
After you'll implement one you can set it in your style as default behavior.