Auto resizing GtkScrolledWindow

I have added three GtkHBox inside a GtkScrolledWindow. And set开发者_开发百科 the size of each box as the size of the window. but, when exposed the size of the Scrolled window is resizing by itself.

But, when i do the same with three Layouts ScrolledWindow size is maintained properly. What could be the reason for this.

GtkHBox doesn't have a scrolling interface. GtkLayout does. You can add a scrolling interface to something that doesn't have one, by putting it into a GtkViewport and then putting the GtkViewport into the GtkScrolledWindow.