我正在尝试根据有关运行循环的线程编程指南编写一个演示。当我实现NSPortDelegate的-(void)handlePortMessage:(NSPortMessage*)portMessage;方法时提示错误:Receivertype'NSPortMessage'forinstancemessageisaforwarddeclaration所以我尝试通过“Foundation/NSPortMessage.h”导入，之后它说:Foundation/NSPortMessage.hfilenotfound.所以我想知道我们是否可以在iOS中使用NSPortMesssage？