目的:指透明的把一个东西换成另一个。在运行时替换。
利用方法混写可以改变那些没有源代码的对象。
该方法大致可以划分为三种:
1)有可能类已经实现的了
2)某个父类实现的方法
3)根本没有实现
前两种 可以通过调用class_getInstanceMethod(<#__unsafe_unretained Class cls#>, <#SEL name#>),成功后会返回一个IMP ,失败则是NULL。
最后一种 可以通过调用class_addMethod(<#__unsafe_unretained Class cls#>, <#SEL name#>, <#IMP imp#>, <#const char *types#>) 如果失败,则此类直接实现了正在混写的方法,那么转而用method_setImplementation(<#Method m#>, <#IMP imp#>)来把就实现替换为新的实现即可。
#import <objc/runtime.h>
@implementation UIViewController (Tracking)
+ (void)load {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
Class class = [self class];
SEL originalSelector = @selector(viewWillAppear:);
SEL swizzledSelector = @selector(xxx_viewWillAppear:);
Method originalMethod = class_getInstanceMethod(class, originalSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
// When swizzling a class method, use the following:
// Class class = object_getClass((id)self);
// ...
// Method originalMethod = class_getClassMethod(class, originalSelector);
// Method swizzledMethod = class_getClassMethod(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);
}
});
}
#pragma mark - Method Swizzling
- (void)xxx_viewWillAppear:(BOOL)animated {
[self xxx_viewWillAppear:animated];
NSLog(@"viewWillAppear: %@", self);
}
@end