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!

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