原文来自:Runtime方法的使用—Class篇
感谢:xietao3

方法交换:

+ (void)load{
    //方法交换应该被保证，在程序中只会执行一次
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        
        //获得viewController的生命周期方法的selector
        SEL systemSel = @selector(viewWillAppear:);
        //自己实现的将要被交换的方法的selector
        SEL swizzSel = @selector(swiz_viewWillAppear:);
        //两个方法的Method
        Method systemMethod = class_getInstanceMethod([self class], systemSel);
        Method swizzMethod = class_getInstanceMethod([self class], swizzSel);
        
        //首先动态添加方法，实现是被交换的方法，返回值表示添加成功还是失败
        BOOL isAdd = class_addMethod(self, systemSel, method_getImplementation(swizzMethod), method_getTypeEncoding(swizzMethod));
        if (isAdd) {
            //如果成功，说明类中不存在这个方法的实现
            //将被交换方法的实现替换到这个并不存在的实现
            class_replaceMethod(self, swizzSel, method_getImplementation(systemMethod), method_getTypeEncoding(systemMethod));
        }else{
            //否则，交换两个方法的实现
            method_exchangeImplementations(systemMethod, swizzMethod);
        }
        
    });
}

- (void)swiz_viewWillAppear:(BOOL)animated{
    //这时候调用自己，看起来像是死循环
    //但是其实自己的实现已经被替换了
    [self swiz_viewWillAppear:animated];// 如果不调用,则原方法的实现将被屏蔽
    NSLog(@"hello");
}

常用方法

- (void)viewDidLoad {
    [super viewDidLoad];
    // 调用方法方案1
//    objc_msgSend(self,@selector(initial:),@"完成初始化");
    // 调用方法方案2
    Method method = [self class_getInstanceMethod:SelfClass selector:@selector(initial:)];
    [self method_invoke:self method:method];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Initialize
- (void)initial:(NSString *)str{
    if (str) NSLog(@"%@",str);
    _person = [[Person alloc] init];
    _person.name = @"xietao";
    _person.age = @"18";
    _person.gender = @"male";
    _person.city = @"shanghai";

    [self logRunTimeAction:nil];
}

#pragma mark - IBAction
- (IBAction)logRunTimeAction:(id)sender {
    objc_property_attribute_t attrs[] = { { "T", "@\"NSString\"" }, { "&", "N" }, { "V", "" } };

    size_t objSize = class_getInstanceSize([_person class]);
    size_t allocSize = 2 * objSize;
    uintptr_t ptr = (uintptr_t)calloc(allocSize, 1);


    // Class
    [self class_getClassName:SelfClass];
    [self class_getSuperClass:SelfClass];
    [self class_getInstanceSize:SelfClass];
    [self class_getInstanceVariable:SelfClass name:"_person"];
    [self class_getClassVariable:SelfClass name:"Person"];
    [self class_getInstanceMethod:SelfClass selector:@selector(class_getInstanceMethod:selector:)];
    [self.class class_getClassMethod:SelfClass selector:@selector(class_getClassMethod:selector:)];
    [self class_getProperty:SelfClass name:"person"];
    [self class_getMethodImplementation:SelfClass selector:@selector(class_getMethodImplementation:selector:)];
    [self class_getMethodImplementation_stret:SelfClass selector:@selector(class_getMethodImplementation_stret:selector:)];
    [self class_copyIvarList:[_person class]];
    [self class_copyPropertyList:[_person class]];
    [self class_copyMethodList:[_person class]];
    [self class_copyProtocolList:[_person class]];
    [self class_addIvar:[_person class] name:"country" size:sizeof(NSString *) alignment:0 types:"@"]; // 无效方法
    [self class_addProperty:[_person class] name:"country" attributes:nil attributeCount:3];
    [self class_addMethod:SelfClass selector:NSSelectorFromString(@"runtimeTestMethod:") imp:nil types:"v@:@"];
    [self class_addProtocol:[_person class] protocol:@protocol(RuntimeBaseProtocol)];
    [self class_replaceProperty:[_person class] name:"country" attributes:nil attributeCount:3];
    [self class_replaceMethod:[_person class] selector:@selector(runtimeTestAction1) imp:class_getMethodImplementation([_person class], @selector(runtimeTestAction2)) types:"v@:"];
    [self class_respondsToSelector:[_person class] selector:@selector(runtimeTestAction1)];
    [self class_isMetaClass:object_getClass(self.superclass)];
    [self class_conformsToProtocol:[_person class] protocol:NSProtocolFromString(@"RuntimeBaseProtocol")];
    [self class_createInstance:[_person class] extraBytes:class_getInstanceSize([_person class])];

}


#pragma mark - Class 创建
- (void)class_createInstance:(Class)class extraBytes:(size_t)extraBytes {
    Person *tempPerson = class_createInstance(class, extraBytes);
    tempPerson.name = @"instance creat Success";
    NSLog(@"%s%@",__func__,tempPerson.name);
}

#pragma mark - Class 类名，父类，元类；实例变量，成员变量；属性；实例方法，类方法，方法实现；
/**
 *  获取类的类名
 *
 *  @param class 类
 */
- (void)class_getClassName:(Class)class {
    NSLog(@"%s:%s",__func__,class_getName(class));
}

/**
 *  获取类的父类
 *
 *  @param class 类
 */
- (void)class_getSuperClass:(Class)class {
    NSLog(@"%s%@",__func__,NSStringFromClass(class_getSuperclass(class)));
}

/**
 *  获取实例大小
 *
 *  @param class 类
 */
- (void)class_getInstanceSize:(Class)class {
    NSLog(@"%s%zu",__func__,class_getInstanceSize(class));
}

/**
 *  获取类中指定名称实例成员变量的信息
 *
 *  @param class 类
 *  @param name  成员变量名
 */
- (void)class_getInstanceVariable:(Class)class name:(const char *)name {
    Ivar ivar = class_getInstanceVariable(class,name);
    NSLog(@"%s%s%s",__func__,[self ivar_getTypeEncoding:ivar],[self ivar_getName:ivar]);
}

/**
 *  获取类成员变量的信息（该函数没有作用，官方解释:http://lists.apple.com/archives/objc-language/2008/Feb/msg00021.html
 *
 *  @param class 类
 *  @param name  成员变量名
 */
- (void)class_getClassVariable:(Class)class name:(const char *)name {
    Ivar ivar = class_getClassVariable(class,name);
    NSLog(@"%s%s%s",__func__,[self ivar_getTypeEncoding:ivar],[self ivar_getName:ivar]);
}

/**
 *  获取属性的信息(与获取成员变量信息类似，不同的是不用打_)
 *
 *  @param class 类
 *  @param name  属性名
 */
- (void)class_getProperty:(Class)class name:(const char *)name {
    objc_property_t property = class_getProperty(class,name);
    NSLog(@"%s%s%s",__func__,[self property_getName:property] ,[self property_getAttributes:property]);
    [self property_copyAttributeList:property];
}

/**
 *  获取类制定方法的信息
 *
 *  @param class    类
 *  @param selector 方法
 */
- (Method)class_getInstanceMethod:(Class)class selector:(SEL)selector {
    Method method = class_getInstanceMethod(class, selector);
    NSLog(@"%s%s%u",__func__,sel_getName(method_getName(method)) ,[self method_getNumberOfArguments:method]);
    return method;
}

/**
 *  获取类方法的信息
 *
 *  @param class    类
 *  @param selector 方法
 */
+ (Method)class_getClassMethod:(Class)class selector:(SEL)selector {
    Method method = class_getClassMethod(class, selector);
    NSLog(@"%s%s%u",__func__,sel_getName(method_getName(method)) ,method_getNumberOfArguments(method));
    return method;
}

/**
 *  获取方法具体实现
 *
 *  @param class    类
 *  @param selector 方法
 *
 *  @return IMP
 */
- (IMP)class_getMethodImplementation:(Class)class selector:(SEL)selector {
    IMP imp = class_getMethodImplementation(class, selector);
    return imp;
}

/**
 *  获取类中的方法的实现,该方法的返回值类型为struct
 *
 *  @param class    类
 *  @param selector 方法
 *
 *  @return IMP
 */
- (IMP)class_getMethodImplementation_stret:(Class)class selector:(SEL)selector {
    IMP imp = class_getMethodImplementation_stret(class, selector);
    return imp;
}

#pragma mark - Class 成员变量列表；属性列表；方法列表；协议列表；
/**
 *  获取成员变量列表
 *
 *  @param class 类
 */
- (void)class_copyIvarList:(Class)class {
    unsigned int count;
    Ivar *ivarList = class_copyIvarList(class, &count);
    NSLog(@"%s",__func__);
    for (int i = 0; i < count; i++) {
        Ivar ivar = ivarList[i];
        // 获取成员属性名
        NSString *name = [NSString stringWithUTF8String:[self ivar_getName:ivar]];
        NSString *type = [NSString stringWithUTF8String:[self ivar_getTypeEncoding:ivar]];
//        NSString *value = object_getIvar(obj, ivar);
        NSLog(@"%@%@",type,name);
    }
}

- (void)class_copyPropertyList:(Class)class {
    unsigned int count;
    objc_property_t *propertyList = class_copyPropertyList(class,&count);
    NSLog(@"%s",__func__);
    for (int i = 0; i < count; i++) {
        objc_property_t property = propertyList[i];
        // 获取成员属性名
        NSString *name = [NSString stringWithUTF8String:[self property_getName:property]];
        NSString *type = [NSString stringWithUTF8String:[self property_getAttributes:property]];
        NSLog(@"%@%@",type,name);
    }
}

/**
 *  获取方法列表
 *
 *  @param class 类
 */
- (void)class_copyMethodList:(Class)class {
    unsigned int count;
    Method *methodList = class_copyMethodList(class,&count);
    for (int i = 0; i < count; i++) {
        Method method = methodList[i];
        NSLog(@"%s%s",__func__,sel_getName(method_getName(method)));
    }
}

/**
 *  获取协议列表
 *
 *  @param class 类
 */
- (void)class_copyProtocolList:(Class)class {
    unsigned int count;
    Protocol **protocolList = class_copyProtocolList(class,&count);
    for (int i = 0; i < count; i++) {
        Protocol *protocol = protocolList[i];
        NSLog(@"%s%s",__func__,[self protocol_getName:protocol]);
    }
}

#pragma mark - Class add: 成员变量；属性；方法；协议
/**
 *  添加成员变量(添加成员变量只能在运行时创建的类，且不能为元类)
 *
 *  @param class     类
 *  @param name      成员变量名字
 *  @param size      大小
 *  @param alignment 对其方式
 *  @param types     参数类型
 */
- (void)class_addIvar:(Class)class name:(const char *)name size:(size_t)size alignment:(uint8_t)alignment types:(const char *)types {

//    if (class_addIvar([_person class], "country", sizeof(NSString *), 0, "@")) {
    if (class_addIvar(class, name, size, alignment, types)) {

        NSLog(@"%sadd ivar success",__func__);
    }else{
        NSLog(@"%sadd ivar fail",__func__);
    }
}

/**
 *  添加属性
 *
 *  @param class          类
 *  @param name           属性名
 *  @param attributes     参数
 *  @param attributeCount 参数数量
 */
- (void)class_addProperty:(Class)class name:(const char *)name attributes:(const objc_property_attribute_t *)attributes attributeCount:(unsigned int)attributeCount {
    objc_property_attribute_t type = { "T", "@\"NSString\"" };
    objc_property_attribute_t ownership = { "&", "N" }; // C = copy
    objc_property_attribute_t backingivar  = { "V", "" };
    objc_property_attribute_t attrs[] = { type, ownership, backingivar };

    if (class_addProperty(class, name, attrs, attributeCount)) {
        NSLog(@"%sadd Property success",__func__);
    }else{
        NSLog(@"%sadd Property fail",__func__);
    }
//    [self class_copyPropertyList:class];
}

/**
 *  添加方法
 *
 *  @param class    类
 *  @param selector 方法
 *  @param imp      方法实现
 *  @param types    类型
 */
- (void)class_addMethod:(Class)class selector:(SEL)selector imp:(IMP)imp types:(const char *)types {
    if (class_addMethod(class,selector,class_getMethodImplementation(class, selector),types)) {
        NSLog(@"%sadd method success",__func__);
    }else{
        NSLog(@"%sadd method fail",__func__);
    }
//    [self class_copyMethodList:class];

}

/**
 *  添加协议
 *
 *  @param class    类
 *  @param protocol 协议
 */
- (void)class_addProtocol:(Class)class protocol:(Protocol *)protocol {
    if (class_addProtocol(class, protocol)) {
        NSLog(@"%sadd protocol success",__func__);
    }else{
        NSLog(@"%sadd protocol fail",__func__);
    }
//    [self class_copyProtocolList:class];
}


#pragma marl - Class replace：属性；方法
/**
 *  替换属性的信息(如果没有原属性会新建一个属性)
 *
 *  @param class          类
 *  @param name           属性名
 *  @param attributes     类型
 *  @param attributeCount 类型数量
 */
- (void)class_replaceProperty:(Class)class name:(const char *)name attributes:(const objc_property_attribute_t *)attributes attributeCount:(unsigned int)attributeCount {
    objc_property_attribute_t type = { "T", "@\"NSString\"" };
    objc_property_attribute_t ownership = { "C", "" }; // C = copy
    objc_property_attribute_t backingivar  = { "V", "" };
    objc_property_attribute_t attrs[] = { type, ownership, backingivar };

    class_replaceProperty(class, name, attrs, 3);
//    [self class_copyPropertyList:class];

}

/**
 *  替代方法的实现
 *
 *  @param class    类
 *  @param selector 被替代的方法
 *  @param imp      替代方法
 *  @param types    类型
 */
- (void)class_replaceMethod:(Class)class selector:(SEL)selector imp:(IMP)imp types:(const char *)types {
    class_replaceMethod(class, selector, imp, types);
    NSLog(@"%s",__func__);
    [_person runtimeTestAction1];
}

#pragma mark - Class 判断
/**
 *  查看类是否相应指定方法
 *
 *  @param class    类
 *  @param selector 方法
 */
- (void)class_respondsToSelector:(Class)class selector:(SEL)selector {
    if (class_respondsToSelector(class,selector)) {
        NSLog(@"%s %@ exist",__func__,NSStringFromClass(class));
    }else{
        NSLog(@"%s %@ non-exist",__func__,NSStringFromClass(class));
    }
}

/**
 *  查看类是否为元类
 *
 *  @param class 类
 */
- (void)class_isMetaClass:(Class)class {
    if (class_isMetaClass(class)) {
        NSLog(@"%s %@ isMetaClass",__func__,NSStringFromClass(class));
    }else{
        NSLog(@"%s %@ non-isMetaClass",__func__,NSStringFromClass(class));
    }
}

/**
 *  查看类是否遵循指定协议
 *
 *  @param class    类
 *  @param protocol 协议
 */
- (BOOL)class_conformsToProtocol:(Class)class protocol:(Protocol *)protocol {
    if (class_conformsToProtocol(class, protocol)) {
        NSLog(@"%s %@ conformsToProtocol %@",__func__,NSStringFromClass(class),NSStringFromProtocol(protocol));
        return YES;
    }else{
        NSLog(@"%s %@ non-conformsToProtocol %@",__func__,NSStringFromClass(class),NSStringFromProtocol(protocol));
        return NO;
    }
}