I created custom class ingeriting from TextBox and I use it in one of my window. Class is in root of project so it's namespace is: Firm 
To use this class from root of project I added line into xaml:
<Window x:Class="Firm.Prijem.PaletaWindow"
        ...
        xmlns:mynms="clr-namespace:Firm"> <--- ADDED LINE
       <mynms:SelectAllTextBox Name="textBoxMnozstvi" />
</Window>
But now when I try to run my code. I got error, because "name 'textBoxMnozstvi' does not exist in current context" on line:
 String text = textBoxMnozstvi.Text;
Why is that? Is now the textBoxMnozstvi in another namespace?
 
     
    