>>Hi,
>>To just answer the question: Since you can't have XAML you would have to do it in code. e.g:

public _ViewBase()
>>        {
>>            StackPanel sp = new StackPanel();
>>            Button b = new Button();
>>            b.Content = "Click me";
>>            sp.Children.Add(b);
>>            this.Content = sp;
>>        }

>>But I agree with John - from a WPF POV this is very unlikely to be the right approach. Are you using MVVM for this app?
>
>I don't think that would work. As soon as you add content to the UserControl it's going to replace your stack panel.
>
>You could do it with view injection.
>
>* Wait till the control is fully loaded.
>* Detach the contents.
>* Add your wrapper.
>* Attach the contents to your wrapper.
>
>But I don't recommend that either.

Another way ( I don't recommend this either :-} ) might be something like:

namespace Junk
{
    public class _ViewBase : UserControl
    {
        public Grid G { get; set; }

        public _ViewBase()
        {
            G = new Grid();
            G.RowDefinitions.Add(new RowDefinition());
            G.RowDefinitions.Add(new RowDefinition());
            Button b = new Button();
            b.Content = "Base Class Button";
            b.SetValue(Grid.RowProperty, 0);
            G.Children.Add(b);
            this.Content = G;
        }

        public ContentControl AddedContent
        {
            get { return (ContentControl)GetValue(AddedContentProperty); }
            set { SetValue(AddedContentProperty, value); }
        }
        static readonly PropertyMetadata m = new FrameworkPropertyMetadata(null, SetContent);

        public static readonly DependencyProperty AddedContentProperty =
            DependencyProperty.Register("AddedContent", typeof(ContentControl), typeof(_ViewBase), m);

        private static void SetContent(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            _ViewBase v = (_ViewBase)d;
            ContentControl c = (ContentControl)e.NewValue;
            c.SetValue(Grid.RowProperty, 1);
            ((_ViewBase)d).G.Children.Add(c);
         }
     }
}

Then

<Window x:Class="Junk.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:Junk">
    < Window.Resources >
        < ContentControl x:Key="Content" >
            < StackPanel >
                < Button >This is the added button< /Button >
            < /StackPanel >
        < /ContentControl >
    < /Window.Resources >
    < local:_ViewBase AddedContent="{StaticResource Content}" / >
< /Window >

Note to Michel (if you see this): The above XAML does not display correctly unless white space is added ??