Any idea why IB doesn't l开发者_运维知识库et me make this connection?

In the Identity Inspector for that views File's Owner, make sure that the Class is set to MainScreenViewController. If you could add a screenshot of your MainScreenViewController.xib window that may be more helpful.
You are trying to link two different IB documents, i.e two different .xib files, which is not possible. I think you really only want to have one .xib file here.
加载中,请稍侯......
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