C# WPF tabs tabcontrol customisation

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C#

WPF

Heys, I currently have a set up that allows me to add and remove new tabs, the only problem is I have problem adding anything to this new tab. I want to have a text box in there but am having troubling adding one, the tabs are just appearing as blank. Any help would be great, thank you!

Here is how I have it setup:

The button that makes a new tab:

<Button
                               FontSize="12"
                               Content="Private Chat"
                               Grid.Column="1" Height="23" HorizontalAlignment="Left" Margin="147,118,0,0" VerticalAlignment="Top" Width="75"
                               Name="btnPrivateChat" Click="btnPrivateChat_Click" />

Which calls this function:

private void btnPrivateChat_Click(object sender, RoutedEventArgs e)
       {

           ListBoxItem userName = lstOnlineUsers.SelectedItem as ListBoxItem;

           if (userName != null)
           {
               TabHandler newTabItem = new TabHandler();
               newTabItem.Title = userName.Content.ToString();
               ;
               ChatTabControl.Items.Add(newTabItem);
               newTabItem.Focus();
               newTabItem.ApplyTemplate();
           }
           else
           {

               MessageBox.Show("Error! Please select a username.");
           }
       }

Which then creates an instance of the usercontrol TabHandler:

public TabHandler()
{
    // Create an instance of the usercontrol
    TabHeader tabHeader = new TabHeader();

Usercontrol TabHandler (XAML) :

<usercontrol x:class="TrapezoidTabs.TabHeader" xmlns:x="#unknown">
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="23" d:DesignWidth="81" Margin="0">
    <grid>
        <Button Content="X"  Height="19" HorizontalAlignment="Right" Margin="0,3,4,0" Name="btnCloseTab" VerticalAlignment="Top" Width="20" FontFamily="Courier" FontWeight="Bold" Style="{StaticResource {x:Static ToolBar.ButtonStyleKey}}" FontStretch="Normal" Visibility="Visible" FontSize="14" Padding="0" ToolTip="Close"/>
        <Label FontSize="14" Foreground="Black" Content="User"  Height="23" HorizontalAlignment="Left" Margin="4,1,0,0" Name="lblTabTitle" VerticalAlignment="Top" />
    </grid>
</usercontrol>

Should I be making a new Window instead of a usercontrol? I realy want to add content to each page. Thanks in advance!