*** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<NSObject 0x6807200> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key f2.'
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主要是因为操作xib连接错误
tableviewcell中的属性连接到自身的控件，而非连接到File's Owner