Controls overlapping tabitem wpf c#

I have a TabControl,inside one Tabitem, i have a grid and my userControl inside the grid:

     <TabControl>
        <TabItem>
        <Grid HorizontalAlignment="Left" Height="64" Margin="288,150,0,0" VerticalAlignment="Top" Width="354">
        <Canvas>
        <local:MyCustomComboBox x:Name="ucc1" HorizontalAlignment="Left" Grid.RowSpan="2" Grid.ColumnSpan="3" Height="30" VerticalAlignment="Top" Width="194" ClipToBounds="True"/>
     <Canvas>
    </Grid>
  <TabItem>
 <TabControl>

By default,when the userControl's size is greater than the grid's/TabItem's size,the extra portion can't be seen.How can i make my UserControl overlap it ? I tried to add RowSpan and ColumnSpan but it didn't work :(

Solution

TabItem has it's own bounds which u cannot overlap.So,there's no way u can achieve your goal ... But i always try my best to help people, so here's a quick tip :

If the usercontrol is bigger than the gird

Your userControl XAML includes MyCustomComboBox, which makes me think it is a combobox..I've seen your previous post where you wanted to customize your combobox but couldn't quite achieve your goals...So, are you trying to create you own custom combobox and by usercontrol bigger than the grid , did u mean that the drop down menu u created doesn't go outside the grid rather is clipped to the grid ??

If this is the case , u can use a ContextMenu and move your custom drop-down list there.Then the contextMenu will overlap both the TabItem and Grid as it is a window itself.

Also , NOTE that u cannot use Named content in usercontrol(u can but that requires a workaround).So i suggest you to add all required code behinds , even set required binding from the user-control's code behind.

Hope this helps :)