header search path in XCode 4

I want to 开发者_高级运维add a path to the header search path. However in the build settings when I double click on the header search path.. it doesn't pop up a new window where I can type.. What am I doing wrong?

Click on the project in the file navigator on the left. Then click on the project or target in the editor that appears. Click on "Build Settings", then change from "Basic" to "All". Its under search paths.