Need some suggestions about how to reference outside control - wpf

Question

I insert a Tabcontrol into a BorderControl. The Tabcontrol used seperate styles. Right now the Close Button inside Tabcontrol can refer to itself. So when click it the TabControl is closed I guess so. Is it possible to refer the button to the Border control outside so that when close the Border control is collpased?
<DockPanel LastChildFill="True">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="160" MinWidth="100"/>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Border Margin="5,5,0,5" BorderBrush="Aqua" BorderThickness="1">
<TabControl Margin="0,15,0,0" Style="{StaticResource StandardTabControl}" >
<TabItem Header="Start">
</TabItem>
</TabControl>
</Border>
<GridSplitter Grid.Column="1" Background="Transparent" Width="6" HorizontalAlignment="Center"></GridSplitter>
<Border Grid.Column="2" BorderBrush="Aqua" BorderThickness="1" Margin="0,5,5,5"></Border>
</Grid>
</DockPanel>
After click the close button
And part of the styles of TabControl.
<Button Grid.Column="1" Height="15" Width="15" HorizontalAlignment="Center" VerticalAlignment="Center">
<i:Interaction.Triggers>
<i:EventTrigger EventName="Click">
<Ac:CloseTabItemAction TabItem="{Binding RelativeSource={RelativeSource AncestorType=TabItem}}"
TabControl="{Binding RelativeSource={RelativeSource AncestorType=TabControl}}">
</Ac:CloseTabItemAction>
</i:EventTrigger>
</i:Interaction.Triggers>
<!--A lot more about styles-->
</Button>

Answer 1

here is a solution using control template triggers in pure xaml
<DockPanel LastChildFill="True">
<Control>
<Control.Template>
<ControlTemplate>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="160"
MinWidth="100"
x:Name="column" />
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Border Margin="5,5,0,5"
BorderBrush="Aqua"
BorderThickness="1">
<TabControl Margin="0,15,0,0"
Style="{StaticResource StandardTabControl}"
x:Name="tabControl">
<TabItem Header="Start">
</TabItem>
</TabControl>
</Border>
<GridSplitter Grid.Column="1"
Background="Transparent"
Width="6"
HorizontalAlignment="Center"></GridSplitter>
<Border Grid.Column="2"
BorderBrush="Aqua"
BorderThickness="1"
Margin="0,5,5,5"></Border>
</Grid>
<ControlTemplate.Triggers>
<DataTrigger Binding="{Binding HasItems,ElementName=tabControl}"
Value="false">
<Setter TargetName="column"
Property="MinWidth"
Value="0" />
<Setter TargetName="column"
Property="Width"
Value="0" />
</DataTrigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Control.Template>
</Control>
</DockPanel>
based on the assumption that when CloseTabItemAction will be called it will remove the TabItem from the TabControl, the trigger will detect the same based on HasItems property and will collapse the column if there are no items
EDIT
based on the comments here are the finding. while resizing GridSplitter sets a Local value to the ColumnDefinition's Width property which have higher precedence than the Trigger values so the Trigger effectively fails to modify the value.
the solution proposed is to use Animation to set the desired value as Animations has higher precedence then the Local value, and the desired value is applied to the property.
<ControlTemplate.Triggers>
<DataTrigger Binding="{Binding HasItems,ElementName=T1}"
Value="false">
<Setter TargetName="Co0"
Property="MinWidth"
Value="0" />
<Setter TargetName="G1"
Property="Width"
Value="0" />
<DataTrigger.EnterActions>
<BeginStoryboard>
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetName="Co0"
Storyboard.TargetProperty="Width">
<DiscreteObjectKeyFrame KeyTime="0:0:0">
<DiscreteObjectKeyFrame.Value>
<GridLength>0</GridLength>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</BeginStoryboard>
</DataTrigger.EnterActions>
</DataTrigger>
</ControlTemplate.Triggers>
in the above code I also make the splitter width to 0 so that there is no empty space on the left