一探iOS 消息查找：叩响代码背后的秘密

2023-10-18 13:51:57

iOS消息查找的幕后故事

作为iOS开发人员，我们每天都在使用消息查找来调用对象的方法。然而，您是否曾经想过消息查找是如何工作的呢？在本文中，我们将深入iOS消息查找的内部机制，揭开它的神秘面纱。

分析底层源码

为了理解消息查找的原理，我们可以分析底层源码。首先，我们需要使用clang将OC代码转化为C++源码。例如，我们可以使用以下命令将Person.h和Person.m文件转化为Person.cpp文件：

clang -rewrite-objc Person.h Person.m -o Person.cpp

转化的结果如下：

namespace std {
struct type_info {
  virtual ~type_info();
};
}
struct _objc_class {
  Class isa;
  Class superclass;
  const char *name;
  long version;
  long info;
  long instance_size;
  struct _objc_ivar_list *ivars;
  struct _objc_method_list **methodLists;
  struct _objc_cache *cache;
  struct _objc_protocol_list *protocols;
};
struct _objc_ivar {
  char *name;
  char *type;
  int offset;
};
struct _objc_method {
  SEL name;
  char *types;
  IMP imp;
};
struct _objc_cache {
  void *buckets;
  struct _objc_hashtable *cache_buckets;
  struct _objc_hashtable *methodLists;
  unsigned int methodCount;
  unsigned int protocolCount;
  struct _objc_protocol_list *protocols;
  unsigned int classSize;
  unsigned int rwSize;
  unsigned int flags;
};
struct _objc_method_list {
  struct _objc_method_list *next;
  unsigned int count;
  struct _objc_method *methods;
  unsigned int method_count;
};
struct _objc_protocol_list {
  struct _objc_protocol_list *next;
  const char *name;
  struct _objc_protocol *protocol;
};
struct _objc_property {
  const char *name;
  const char *attributes;
};
struct _objc_class_ro {
  unsigned int flags;
  unsigned int instanceStart;
  unsigned int instanceSize;
  unsigned int reserved;
};
struct _objc_super {
  struct _objc_class *receiver;
  struct _objc_class *super_class;
};
struct _prop_t {
  const char *name;
  const char *attributes;
};
struct _objc_method {
  SEL name;
  char *types;
  IMP imp;
};
struct _objc_property {
  const char *name;
  const char *attributes;
};
struct _objc_class {
  Class isa;
  Class superclass;
  const char *name;
  long version;
  long info;
  long instance_size;
  struct _objc_ivar_list *ivars;
  struct _objc_method_list **methodLists;
  struct _objc_cache *cache;
  struct _objc_protocol_list *protocols;
};
...