以forkingdog的PorotocolKit举例
举例
ProtocolKit Protocol extension for Objective-C Usage Your protocol: @protocol Forkable <NSObject> @optional
- (void)fork; @required
- (NSString *)github; @end
Protocol extension, add default implementation, use @defs magic keyword @defs(Forkable) - (void)fork {
NSLog(@"Forkable protocol extension: I'm forking (%@).", self.github);
} - (NSString *)github {
return @"This is a required method, concrete class must override me.";
} @end
Your concrete class @interface Forkingdog : NSObject <Forkable>
@end @implementation Forkingdog - (NSString *)github {
return @"https://github.com/forkingdog";
} @end
Run test [[Forkingdog new] fork];
Result [Console] Forkable protocol extension: I'm forking (https://github.com/forkingdog).
实现
我们可以看到关键字是@def 查看其定义是
// For a magic reserved keyword color, use @defs(your_protocol_name)
#define defs _pk_extension // Interface
#define _pk_extension($protocol) _pk_extension_imp($protocol, _pk_get_container_class($protocol)) // Implementation
#define _pk_extension_imp($protocol, $container_class) \
protocol $protocol; \
@interface $container_class : NSObject <$protocol> @end \
@implementation $container_class \
+ (void)load { \
_pk_extension_load(@protocol($protocol), $container_class.class); \
} \ // Get container class name by counter
#define _pk_get_container_class($protocol) _pk_get_container_class_imp($protocol, __COUNTER__)
#define _pk_get_container_class_imp($protocol, $counter) _pk_get_container_class_imp_concat(__PKContainer_, $protocol, $counter)
#define _pk_get_container_class_imp_concat($a, $b, $c) $a ## $b ## _ ## $c
转化为oc语言定义就是
@protocol Forkable; \
@interface __PKContainer_Forkable_0 : NSObject <Forkable> @end \
@implementation __PKContainer_Forkable_0 \
@synthesize title = _title; + (void)load { \
//add protocol class method?
_pk_extension_load(@protocol(Forkable), __PKContainer_Forkable_0.class);
} -(NSString *)title
{
if (!_title) {
_title = @"default title!";
}
return _title;
} - (void)fork {
NSLog(@"Forkable protocol extension: I'm forking (%@).", self.github);
} - (NSString *)github {
return @"This is a required method, concrete class must override me.";
}
@end
从这可以看出关键的代码 _pk_extension_load()
可以猜想其定义是
1 在load里注册自己包含那些扩展协议
2 在c方法里遍历所有的类 把有扩展的 方法的实现指过去
现在查看其函数实现 关键代码如下
__attribute__((constructor)) static void _pk_extension_inject_entry(void) {
pthread_mutex_lock(&protocolsLoadingLock);
unsigned classCount = ;
Class *allClasses = objc_copyClassList(&classCount);
@autoreleasepool {
for (unsigned protocolIndex = ; protocolIndex < extendedProtcolCount; ++protocolIndex) {
PKExtendedProtocol extendedProtcol = allExtendedProtocols[protocolIndex];
for (unsigned classIndex = ; classIndex < classCount; ++classIndex) {
Class class = allClasses[classIndex];
if (!class_conformsToProtocol(class, extendedProtcol.protocol)) {
continue;
}
_pk_extension_inject_class(class, extendedProtcol);
}
}
}
pthread_mutex_unlock(&protocolsLoadingLock);
free(allClasses);
free(allExtendedProtocols);
extendedProtcolCount = , extendedProtcolCapacity = ;
}
//将协议的方法添加到到类中(如果不存在就不添加了)//包括类方法和实例方法
static void _pk_extension_inject_class(Class targetClass, PKExtendedProtocol extendedProtocol) { for (unsigned methodIndex = 0; methodIndex < extendedProtocol.instanceMethodCount; ++methodIndex) {
Method method = extendedProtocol.instanceMethods[methodIndex];
SEL selector = method_getName(method); if (class_getInstanceMethod(targetClass, selector)) {
continue;
} IMP imp = method_getImplementation(method);
const char *types = method_getTypeEncoding(method);
class_addMethod(targetClass, selector, imp, types);
} Class targetMetaClass = object_getClass(targetClass);
for (unsigned methodIndex = 0; methodIndex < extendedProtocol.classMethodCount; ++methodIndex) {
Method method = extendedProtocol.classMethods[methodIndex];
SEL selector = method_getName(method); if (selector == @selector(load) || selector == @selector(initialize)) {
continue;
}
if (class_getInstanceMethod(targetMetaClass, selector)) {
continue;
}
IMP imp = method_getImplementation(method);
const char *types = method_getTypeEncoding(method);
class_addMethod(targetMetaClass, selector, imp, types);
}
}
由此可知猜想是正确的，方法告诉我们对于某一个含有该协议的类，如果其含有了协议里面的函数，则跳过，如果没有该函数就添加。
这里是下载地址