如果我们想要在viewWillApper:的方法里做APM可以使用方法调和
给UIViewController添加一个Categroy
#import "UIViewController+Tracking.h"
#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(hsk_viewWillAppear:);
Method originalMethod = class_getInstanceMethod(class, originalSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
// //选择器使用原先的，但是函数实现的指针使用现在的。
// 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
//改变一个实例的方法
- (void)hsk_viewWillAppear:(BOOL)animated{
[self hsk_viewWillAppear:animated];
NSLog(@" %@ %@",NSStringFromClass([self class]) ,NSStringFromSelector(_cmd));
}
load 方法只要文件存在于Xcode 的文件管理器中就一定会调用，
而initialize 程序有调用到这个类的方法才会用到
如果在这个类里面重写load,这initialize 就会调用到。
在ViewController里面调用
- (void)viewWillAppear:(BOOL)animated{
//如果有categroy 他回去找Categroy的实现
//真神奇
[super viewWillAppear:animated];
}
另外想交换NSDictionary 的objectForKey:方法
但是为什么不成功呢？ 是因为这个方法带有返回值吗？
#import "NSDictionary+safeObjectForKey.h"
#import <objc/runtime.h>
@implementation NSDictionary (safeObjectForKey)
+ (void)load{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
SEL originalSelector = @selector(objectForKey:);
SEL swizzledSelector = @selector(safeObjectForKey:);
Class class = [self class];
//拿到实例方法实现的函数指针
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);
}
});
}
//FIXME:为什么带有返回值得方法使用swizzling 不行呢？
- (id)safeObjectForKey:(NSString *)key{
id obj = [self safeObjectForKey:key];
if (!obj) {
NSLog(@"key为%@字典对应的值是nil",key);
return nil;
}
return obj;
}
@end
