Here's how to dynamically add objects to a StackPanel in code-behind:
On our XAML page add a StackPanel tag and add a x:Name attrribute:
<stackpanel horizontalalignment="Left" x:name="Stack1">
</stackpanel>
In the code-behind create the new element and add it to the Children collection:
public MainPage()
{
TextBox TextObj;
InitializeComponent();
TextObj = new TextBox();
TextObj.Width = 100;
Stack1.Children.Add(TextObj);
}