iOS下RunTime分析二（协议C++源码）

这里主要是解释iOS下RunTime分析一（OC文件编译为C++）中的第5点疑问。

先看协议部分的OC源码

头文件：

@protocol ChildDelegate <NSObject>
@optional
- (void)optionalMethod;
@property (nonatomic, strong) NSObject *optionalObj;

@required
- (void)requiredMethod:(NSString *)obj;
@property (nonatomic, strong) NSObject *requiredObj;
@end

@interface ChildObject : MyObject
<NSCopying, ChildDelegate>

@end

源文件：

@interface ChildObject ()
{
    int childA;
    NSObject *childObj;
}
@property (nonatomic, strong) NSString *childName;
@end

@implementation ChildObject
@synthesize requiredObj = _requiredObj;

+ (void)showChildClassMethod
{
    NSLog(@"child object");
}

- (void)childInstanceMethod
{
    NSLog(@"child instance object");
}

- (id)copyWithZone:(NSZone *)zone
{
    return nil;
}

- (void)optionalMethod
{
    
}

- (void)requiredMethod:(NSString *)obj
{
    
}

@end

现在来看下编译成C++之后的源代码，与RunTime分析一相似的部分，不在重新写了。

会生成一个protocol的结构体：

struct _protocol_t {
	void * isa;  // NULL
	const char *protocol_name;
	const struct _protocol_list_t * protocol_list; // super protocols
	const struct method_list_t *instance_methods;
	const struct method_list_t *class_methods;
	const struct method_list_t *optionalInstanceMethods;
	const struct method_list_t *optionalClassMethods;
	const struct _prop_list_t * properties;
	const unsigned int size;  // sizeof(struct _protocol_t)
	const unsigned int flags;  // = 0
	const char ** extendedMethodTypes;
};

以及与protocol相关的一些全局静态变量：

(used, section ("__DATA,__objc_const"))
static const char *_OBJC_PROTOCOL_METHOD_TYPES_NSCopying [] = 
{
	"@24@0:8^{_NSZone=}16"
};

(used, section ("__DATA,__objc_const"))
static struct /*_method_list_t*/ {
	unsigned int entsize;  // sizeof(struct _objc_method)
	unsigned int method_count;
	struct _objc_method method_list[1];
} _OBJC_PROTOCOL_INSTANCE_METHODS_NSCopying  = {
	sizeof(_objc_method),
	1,
	{ {(struct objc_selector *)"copyWithZone:", "@24@0:8^{_NSZone=}16", 0} }
};

struct _protocol_t _OBJC_PROTOCOL_NSCopying = {
	0,
	"NSCopying",
	0,
	(const struct method_list_t *)&_OBJC_PROTOCOL_INSTANCE_METHODS_NSCopying,
	0,
	0,
	0,
	0,
	sizeof(_protocol_t),
	0,
	(const char **)&_OBJC_PROTOCOL_METHOD_TYPES_NSCopying
};

struct _protocol_t *_OBJC_LABEL_PROTOCOL_$_NSCopying = &_OBJC_PROTOCOL_NSCopying;

以上是NSCopying的协议的生成代码。

下面来继续看ChildDelegate协议的生成代码：

(used, section ("__DATA,__objc_const"))
static const char *_OBJC_PROTOCOL_METHOD_TYPES_ChildDelegate = 
{
	"v24@0:8@\"NSString\"16",
	"@\"NSObject\"16@0:8",
	"v24@0:8@\"NSObject\"16",
	"v16@0:8",
	"@\"NSObject\"16@0:8",
	"v24@0:8@\"NSObject\"16"
};

//因为ChildDelegate是继承自NSObojce协议的，所以会多出来这个结构体
(used, section ("__DATA,__objc_const"))
static struct /*_protocol_list_t*/ {
	long protocol_count;  // Note, this is 32/64 bit
	struct _protocol_t *super_protocols[1];
} _OBJC_PROTOCOL_REFS_ChildDelegate = {
	1,
	&_OBJC_PROTOCOL_NSObject
};

//@required 方法
(used, section ("__DATA,__objc_const"))
static struct /*_method_list_t*/ {
	unsigned int entsize;  // sizeof(struct _objc_method)
	unsigned int method_count;
	struct _objc_method method_list[3];
} _OBJC_PROTOCOL_INSTANCE_METHODS_ChildDelegate = {
	sizeof(_objc_method),
	3,
	{ {(struct objc_selector *)"requiredMethod:", "v24@0:8@16", 0},
	{(struct objc_selector *)"requiredObj", "@16@0:8", 0},
	{(struct objc_selector *)"setRequiredObj:", "v24@0:8@16", 0} }
};

//optional 方法
(used, section ("__DATA,__objc_const"))
static struct /*_method_list_t*/ {
	unsigned int entsize;  // sizeof(struct _objc_method)
	unsigned int method_count;
	struct _objc_method method_list[3];
} _OBJC_PROTOCOL_OPT_INSTANCE_METHODS_ChildDelegate = {
	sizeof(_objc_method),
	3,
	{ {(struct objc_selector *)"optionalMethod", "v16@0:8", 0},
	{(struct objc_selector *)"optionalObj", "@16@0:8", 0},
	{(struct objc_selector *)"setOptionalObj:", "v24@0:8@16", 0} }
};

//property
(used, section ("__DATA,__objc_const"))
static struct /*_prop_list_t*/ {
	unsigned int entsize;  // sizeof(struct _prop_t)
	unsigned int count_of_properties;
	struct _prop_t prop_list[2];
} _OBJC_PROTOCOL_PROPERTIES_ChildDelegate = {
	sizeof(_prop_t),
	2,
	{ {"optionalObj","T@\"NSObject\",&,N"},
	{"requiredObj","T@\"NSObject\",&,N"} }
};

struct _protocol_t _OBJC_PROTOCOL_ChildDelegate = {
	0,
	"ChildDelegate",
	&_OBJC_PROTOCOL_REFS_ChildDelegate,
	&_OBJC_PROTOCOL_INSTANCE_METHODS_ChildDelegate,
	0,
	)&_OBJC_PROTOCOL_OPT_INSTANCE_METHODS_ChildDelegate,
	0,
	&_OBJC_PROTOCOL_PROPERTIES_ChildDelegate,
	sizeof(_protocol_t),
	0,
	&_OBJC_PROTOCOL_METHOD_TYPES_ChildDelegate
};
struct _protocol_t *_OBJC_LABEL_PROTOCOL_$_ChildDelegate = &_OBJC_PROTOCOL_ChildDelegate;

……

以此类推如何还实现了其他的协议，那么又会生成一个_protocol_t结构体的对象。

生成的一系列_protocol_t这个结构体对象，最终会被组织成一个_protocol_list_t类型的结构体对象，如下：

(used, section ("__DATA,__objc_const"))
static struct /*_protocol_list_t*/ {
	long protocol_count;  // Note, this is 32/64 bit
	struct _protocol_t *super_protocols[2];
} _OBJC_CLASS_PROTOCOLS_$_ChildObject = {
	2,
	{&_OBJC_PROTOCOL_NSCopying,
	 &_OBJC_PROTOCOL_ChildDelegate}
};

生成的_OBJC_CLASS_PROTOCOLS_$_ChildObject会被加到RO_ChildObject中去。

(used, section ("__DATA,__objc_const"))
static struct _class_ro_t RO_ChildObject = {
	0, __OFFSETOFIVAR__(struct ChildObject, childA), 
	sizeof(struct ChildObject_IMPL), 
	(unsigned int)0, 
	0, 
	"ChildObject",
	&_OBJC_$_INSTANCE_METHODS_ChildObject,
	&_OBJC_CLASS_PROTOCOLS_$_ChildObject,
	&_OBJC_$_INSTANCE_VARIABLES_ChildObject,
	0, 
	0, 
};

总结：

一个OC对象类实现了n个协议就会生成对应的n个_protocol_t的结构体对象，而这些对象最终会被放到一个_protocol_list_t结构体中赋值给该类对象的一个变量中。