Strange issue when I using GtkScrolledWindow in glade

Question

I want to wrap a listbox widget into a scrolled widget, then I find the GtkScrolledWindow, however, I could not drag and drop a GtkListBox into GtkScrolledWindow. I also tried right click the GtkListBox, select Add Parent then Scrolled Window like the following snapshot.

But, I could make it work by manual modify the glade ui file.

So I want to know Why and How to do it in glade.

Answer 1

José Fonte's answer is right, I need to wrap the content into a viewport first, then make the viewport as a child of scrolledWindow.