VS can't find Thumb

Question

I have a form and 2 PictureBoxes inside. One is the background and is static(I don't move and resize it in runtime). I want the 2nd PictureBox to change its size when I drag the corner of it. So I found that Thumb can help me in this problem. You can look here. But when I typed Thumb thumb; in code the VS said to me the next error. I don't understand where is the problem and what i do wrong. Please, explain me how to use Thumb in my application or how to resize the pictureBox in runtime in other ways.

Answer 1

Because it's only available in WPF projects.

Edit : As for resizing the control at runtime, check this other SO question

Answer 2

There is a using missing in your code. Add using System.Windows.Controls.Primitives; to the using section of that code file.