运行时 - class_addMethod 中的“@@:”是什么意思？

Question

使用class_addMethod代码：

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class_addMethod(newClass, @selector(inputAccessoryView), accessoryImp, "@@:");\n

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该方法中参数“@@:”的含义是什么？

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文档：

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/** \n * Adds a new method to a class with a given name and implementation.\n * \n * @param cls The class to which to add a method.\n * @param name A selector that specifies the name of the method being added.\n * @param imp A function which is the implementation of the new method. The function must take at least two arguments\xe2\x80\x94self and _cmd.\n * @param types An array of characters that describe the types of the arguments to the method. \n * \n * @return YES if the method was added successfully, otherwise NO \n *  (for example, the class already contains a method implementation with that name).\n *\n * @note class_addMethod will add an override of a superclass\'s implementation, \n *  but will not replace an existing implementation in this class. \n *  To change an existing implementation, use method_setImplementation.\n */\nOBJC_EXPORT BOOL class_addMethod(Class cls, SEL name, IMP imp, \n                             const char *types) \nOBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);\n

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Answer 1

该types参数描述了\n方法的参数和返回类型，如\n中所述class_addMethod：

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描述方法参数类型的字符数组。有关可能的值，请参阅Objective-C 运行时编程指南 > 类型编码。由于该函数必须至少采用两个参数 \xe2\x80\x94self和_cmd，因此第二个和第三个字符必须是 \xe2\x80\x9c@:\xe2\x80\x9d （第一个字符是返回类型）。

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"@@:"描述了一个方法，返回一个对象\n(类型编码@，在你的情况下：) UIView *，并且除了固定（隐藏）参数self（@对象的类型编码）和（选择器的_cmd类型编码）之外不接受任何参数。:

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