iOS----runtime 运行时机制04--(方法交换)

1、同一个类中两个方法交换

交换方法

- (void)setBadgeValue:(NSString *)badgeValue 和 - (void)wb_setBadgeValue:(NSString *)badgeValue的实现

@implementation UITabBarItem (BadgeValueImage)

+ (void)load{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class clazz = [self class];
        
        // 获取到原来的方法与需要交互的SEL
        SEL originalSelector = @selector(setBadgeValue:);
        SEL swizzledSelector = @selector(wb_setBadgeValue:);
        
        // 通过SEL 获取到类身上的Method
        Method originalMethod = class_getInstanceMethod(clazz, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(clazz, swizzledSelector);
        
        // 向类身上添加方法
        BOOL result = class_addMethod(clazz, swizzledSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
        
        if (result) {
            // 如果添加成功就替换方法实现
            class_replaceMethod(clazz, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
        }else{
            // 没有添加成功，直接交换方法实现
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

- (void)wb_setBadgeValue:(NSString *)badgeValue{
    //调用父类
    [self wb_setBadgeValue:badgeValue];
    
    // 实现逻辑
    // 如果badgeValue为nil 的话。直接返回
    if(!badgeValue){
        return;
    }
    
    // 我们直接能够拿到的就是WBTabBar
    UITabBarController *target = [self valueForKeyPath:@"_target"];
    
    for (UIView *tabBarChild in target.tabBar.subviews) {
        //找UITabBarButton
        if ([tabBarChild isKindOfClass:NSClassFromString(@"UITabBarButton")]) {
            for (UIView *tabBarButtonChild in tabBarChild.subviews) {
                if ([tabBarButtonChild isKindOfClass:NSClassFromString(@"_UIBadgeView")]) {
                    for (UIView *badgeViewChild in tabBarButtonChild.subviews) {
                        if ([badgeViewChild isKindOfClass:NSClassFromString(@"_UIBadgeBackground")]) {
                            //NSLog(@"终于找到你,还好没放弃");
                            unsigned int count;//获取完成之后,count的值就代码当前类身上成员变量的个数
                            
                            //获取类身上的成员变量
                            Ivar *vars = class_copyIvarList(NSClassFromString(@"_UIBadgeBackground"), &count);
                            //遍历查看
                            for (int i=0; i<count; i++) {
                                Ivar var = vars[i];
                                
                                //获取var的名字
                                NSString *name = [NSString stringWithCString:ivar_getName(var) encoding:NSUTF8StringEncoding];
                                //获取类型
                                NSString *type = [NSString stringWithCString:ivar_getTypeEncoding(var) encoding:NSUTF8StringEncoding];
                                
                                NSLog(@"%@=====%@",name,type);
                                //
                                if ([name isEqualToString:@"_image"]) {
                                    //通过kvc赋值
                                    [badgeViewChild setValue:[UIImage imageNamed:self.badgeImageName] forKeyPath:name];
                                }
                            }
                            //释放内存
                            free(vars);
                        }
                    }
                }
            }
        }
    }
}

2、交换两个类中某个方法的实现

交换 Person类中 - (void)personEat; 和Dog类中 - (void)dogEat; 中的实现

Person.h

#import <Foundation/Foundation.h>

@interface Person : NSObject


- (void)personEat;


@end

person.m

#import "Person.h"
#import "Dog.h"
#import <objc/runtime.h>

@implementation Person

+ (void)load{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        //1,拿着class
        Class personClass = [self class];
        Class dogClass = [Dog class];
        
        //2.获取两个方法的sel
        SEL originalSEL = @selector(personEat);
        SEL swizzledSEL = @selector(dogEat);
        
        //3.通过sel获取到class身上的method
        Method originalMethod = class_getInstanceMethod(personClass, originalSEL);
        Method swizzledMethod = class_getInstanceMethod(dogClass, swizzledSEL);
        
        //4执行方法添加-->添加方法是添加的其他类里面的方
        BOOL result = class_addMethod(personClass, swizzledSEL, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
        
        //5如果添加成功,就把添加的方法的实现与原来的方法进行替换
        if (result) {
            class_replaceMethod(personClass, originalSEL, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
            
        }else{
            //6.如果添加不成功,就直接交换方法实现
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

- (void)personEat{
    NSLog(@"人在吃东西");
}

@end

Dog.h

#import <Foundation/Foundation.h>

@interface Dog : NSObject

- (void)dogEat;

@end

Dog.m

#import "Dog.h"

@implementation Dog

- (void)dogEat{
    NSLog(@"狗在吃东西");
}

@end

此时调用 

    Person *p = [[Person alloc]init];

    [p personEat]；

结果会是：狗在吃东西