How to get rid of the 1 pixel white line at the left edge of the window?

I am doing c开发者_如何学Goocoa desktop application and I noticed that there is 1 pixel white line at the left edge which looks pretty ugly for my background.

Is there any way to get rid of it? Thanks!

Make sure you expand the frame of your window's content view to be exactly big enough so there's no white line.