macOS objc_msgSend

1. 变化

• macOS升级到10.15后，宏OBJC_OLD_DISPATCH_PROTOTYPES的值变为0，导致objc_msgSend 定义发生变化。

#if !OBJC_OLD_DISPATCH_PROTOTYPES
OBJC_EXPORT void objc_msgSend(void /* id self, SEL op, ... */ )
    OBJC_AVAILABLE(10.0, 2.0, 9.0, 1.0);
OBJC_EXPORT void objc_msgSendSuper(void /* struct objc_super *super, SEL op, ... */ )
    OBJC_AVAILABLE(10.0, 2.0, 9.0, 1.0);
#else
/** 
 * Sends a message with a simple return value to an instance of a class.
 * 
 * @param self A pointer to the instance of the class that is to receive the message.
 * @param op The selector of the method that handles the message.
 * @param ... 
 *   A variable argument list containing the arguments to the method.
 * 
 * @return The return value of the method.
 * 
 * @note When it encounters a method call, the compiler generates a call to one of the
 *  functions \c objc_msgSend, \c objc_msgSend_stret, \c objc_msgSendSuper, or \c objc_msgSendSuper_stret.
 *  Messages sent to an object’s superclass (using the \c super keyword) are sent using \c objc_msgSendSuper; 
 *  other messages are sent using \c objc_msgSend. Methods that have data structures as return values
 *  are sent using \c objc_msgSendSuper_stret and \c objc_msgSend_stret.
 */
OBJC_EXPORT id objc_msgSend(id self, SEL op, ...)
    OBJC_AVAILABLE(10.0, 2.0, 9.0, 1.0);
/** 
 * Sends a message with a simple return value to the superclass of an instance of a class.
 * 
 * @param super A pointer to an \c objc_super data structure. Pass values identifying the
 *  context the message was sent to, including the instance of the class that is to receive the
 *  message and the superclass at which to start searching for the method implementation.
 * @param op A pointer of type SEL. Pass the selector of the method that will handle the message.
 * @param ...
 *   A variable argument list containing the arguments to the method.
 * 
 * @return The return value of the method identified by \e op.
 * 
 * @see objc_msgSend
 */
OBJC_EXPORT id objc_msgSendSuper(struct objc_super *super, SEL op, ...)
    OBJC_AVAILABLE(10.0, 2.0, 9.0, 1.0);
#endif 

2. 方案

• 原代码：

Class cls = objc_getClass("NSApplication");
objc_object* appInst = objc_msgSend((objc_object*)cls, 
                       sel_registerName("sharedApplication"));

• 修改后：

Class cls = objc_getClass("NSApplication");
objc_object* appInst = ((objc_object * (*)(objc_object *, SEL)) objc_msgSend)((objc_object*)cls, 
                       sel_registerName("sharedApplication"));

本文地址：https://blog.csdn.net/luoshabugui/article/details/108579532