OC runtime 底层API解析

1. 关于class的API

1. object_getClass(instance) //获取isa指向的class
2. object_setClass(instance, [JWStudent class]);//设置isa指向的class
3. object_isClass(id) //判断是否是类对象
4. object_isMetaClass(Class cls) //判断是否是元类对象
5.      //动态创建一个类 跟使用
        Class newClass = objc_allocateClassPair([NSObject class], "JWCat", 0);
        //添加成员变量
        class_addIvar(newClass, "_age", sizeof(int), log2(_Alignof(int)), @encode(int));
        class_addIvar(newClass, "_weight", sizeof(NSString *), log2(_Alignof(NSString *)), @encode(NSString *));
        //添加方法
        class_addMethod(newClass, @selector(run), (IMP)test1, "v16@:0");
        //注册类
        objc_registerClassPair(newClass);
        //使用
        id cls = [[newClass alloc]init];
        //赋值
        [cls setValue:@12 forKey:@"_age"];
        [cls setValue:@"80kg" forKey:@"_weight"];
        [cls run];
        NSLog(@"%@----%@",[cls valueForKey:@"_age"],[cls valueForKey:@"_weight"]);

6.拷贝成员变量列表
        JWPerson * p = [JWPerson new];
        unsigned int count;
        Ivar * ivars = class_copyIvarList([JWPerson class], &count);
        for (int i = 0 ; i< count; i++) {
            Ivar ivar = ivars[i];
            NSLog(@"%s----%s",ivar_getName(ivar),ivar_getTypeEncoding(ivar));
        }
        free(ivars);

2. 交换方法API

• 替换方法的实现

class_replaceMethod(Class cls,IMP imp,const char *types);

• 交换方法的实现

//交换方法
        Method m1 = class_getInstanceMethod([JWPerson class], @selector(print));
        Method m2 = class_getInstanceMethod([JWPerson class], @selector(test));
        
        method_exchangeImplementations(m1, m2);
        
        JWPerson * p = [JWPerson new];
        [p print];
        [p test];