uncaught exception 'NSUnknownKeyException', reason: '[ setValue:forUndefinedKey:]:this class is not key value coding-compliant for the XXX.

the problem is in the xib or storyboard file. You have an item (probably a UIButton) linked to xxx, but you renamed that item to playbtn in code, without reassigning the outlet in the xib. Check the play button in your xib/storyboard and remove its non existent outlet.

storyboard设置问题，检查里面的item是否重复设置或者没有在view controller里面设置该item的outlet