Xcode File Browsing doesn't open files!

Previously when I browsed source code files using Xcode's file browser (located on left side), clicking on a source file would open it in the right window.

I must've accidentally changed some setting that stops this behavior -- now single clicking on any file doesn't do anything at all. I'd really like it to go back to the old behavior of opening the file.

开发者_开发知识库

Any ideas? This behavior is driving me crazy. To open a source file I have to double-click and open in a separate window.

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Quit and restart Xcode.