RunTime--Method Swizzling
method swizzling 修改方法函数的调用
项目中用到的场景:打开页面显示的次数;
用到的函数:
@selector(方法名)
class_getInstanceMethod(<#类名#>, <#方法名(sel)#>)//返回类名下sel方法
class_addMethod(<#__unsafe_unretained Class cls#>, <#SEL name#>, <#IMP imp#>, <#const char *types#>)//给cls添加一个新的方法,若干cls存在这个方法则返回失败
IMP class_getMethodImplementation(Class cls, SEL name)//返回cls的name方法的调用地址
IMP class_replaceMethod(Class cls, SEL name, IMP imp, const char *types)//替换cls的name方法的指针
void method_exchangeImplementations(Method m1, Method m2)//交换两个方法的实现指针
代码:
+ (void)load { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ Class class = [self class]; // When swizzling a class method, use the following: // Class class = object_getClass((id)self); SEL originalSelector = @selector(viewWillAppear:); SEL swizzledSelector = @selector(avc_viewWillAppear:); Method originalMethod = class_getInstanceMethod(class, originalSelector); Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector); BOOL didAddMethod = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod)); if (didAddMethod) { class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod)); } else { method_exchangeImplementations(originalMethod, swizzledMethod); } }); } - (void)avc_viewWillAppear:(BOOL)anmimation{ [self avc_viewWillAppear:anmimation]; NSLog(@"%@",self); }
函数写在load方法里,load方法会在类初始调用,由于method swizzling会影响到类的全局状态,因此要尽量避免在并发处理中出现竞争的情况。+load能保证在类的初始化过程中被加载,并保证这种改变应用级别的行为的一致性。相比之下,+initialize在其执行时不提供这种保证—事实上,如果在应用中没为给这个类发送消息,则它可能永远不会被调用。