Can't add my custom user control in main windows WPF
<p>I can't add My user control to MainWindow.xaml</p>

<p>This is my solution explorer : (pointer show my user Control)</p>

<p><a href="https://i.stack.imgur.com/wuVxQ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wuVxQ.jpg" alt="Solution Explorer"></a></p>

<p>This is my user control header xaml file</p>

<pre><code>&lt;UserControl x:Class="SIManager.ucAddDevices"
         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" 
         xmlns:local="clr-namespace:SIManager"
         mc:Ignorable="d" 
         d:DesignHeight="500" d:DesignWidth="500" FlowDirection="RightToLeft" FontFamily="B Nazanin"&gt;
</code></pre>

<p>And this is MainWindows Header Xaml</p>

<pre><code>&lt;Window x:Class="SIManager.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:SIManager"
    mc:Ignorable="d"
    Title="MainWindow" Height="600" Width="800"&gt;
</code></pre>

<p>And now I can`t add my user control to tab item ... Why ?</p>

<p>In picture below My user control name wont appear ... !!!!</p>

<p><a href="https://i.stack.imgur.com/DMdb6.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DMdb6.jpg" alt="enter image description here"></a></p>

<p>how I can add my user control to Tab  Item ????</p>