objective-c – 为什么即使在调用它之后我也无法获得我的类别实例方法？

我试图更好地理解Objective-C运行时.考虑NSAttributedString.h,它具有最小的接口,后跟更广泛的类别NSExtendedAttributedString.

现在考虑以下代码：

NSAttributedString *attributedString = [[NSAttributedString alloc] initWithAttributedString:[[NSAttributedString alloc] initWithString:@"ABC"]];
NSLog(@"Result: %@",attributedString); 
NSLog(@"Exists? %@",[NSString StringWithUTF8String:sel_getName(method_getName(class_geTinstanceMethod(NSAttributedString.class,@SELEctor(initWithAttributedString:))))]);    
NSLog(@"Exists? %@",@SELEctor(String))))]);

// Produces this output
2013-04-19 10:17:35.364 TestApp[53300:c07] Result: ABC{
}
2013-04-19 10:17:35.364 TestApp[53300:c07] Exists? <null SELEctor>
2013-04-19 10:17:35.365 TestApp[53300:c07] Exists? String

我们发现实例方法是规范接口的一部分,但不是类别中的实例方法.这怎么可能发生,但它可以被成功调用？有没有办法反省并找到类别方法？

NSLog(@"Class: %@",[attributedString class]);

// Produces this output
2013-04-19 19:50:21.955 TestApp[1611:303] Class: NSConcreteAttributedString