KVC 使用方法详解及底层实现你要知道的KVC、KVO、Delegate、Notification都在这里

//获取属性名为key的属性的值
- (nullable id)valueForKey:(NSString *)key;

//设置属性名为key的属性的值为value
- (void)setValue:(nullable id)value forKey:(NSString *)key;

/*
提供一种类似于Java ONGL语法来访问嵌套属性
获取嵌套属性名为keyPath的属性的值
*/
- (nullable id)valueForKeyPath:(NSString *)keyPath;

//设置嵌套属性名为keyPath的属性的值为value
- (void)setValue:(nullable id)value forKeyPath:(NSString *)keyPath;

/*
获取属性名为key的属性值时，如果属性不存在则执行该方法，可自定义实现，
默认实现方式为抛出NSUnknownKeyException异常
*/
- (nullable id)valueForUndefinedKey:(NSString *)key;

/*
设置属性名为key的属性值为value时，如果属性不存在则执行该方法，可自定义实现，
默认实现方式为抛出NSUnknownKeyException异常
*/
- (void)setValue:(nullable id)value forUndefinedKey:(NSString *)key;

//Phone类
@interface Phone : NSObject
@property (nonatomic, strong) NSString *phoneNumber;
@end

@implementation Phone
@synthesize phoneNumber = _phoneNumber;
@end

//Person类
@interface Person : NSObject

@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) NSUInteger age;
//组合一个Phone的对象
@property (nonatomic, strong) Phone *phone;
- (void)showMyself;

@end

@implementation Person

@synthesize name = _name;
@synthesize age = _age;
@synthesize phone = _phone;

- (void)showMyself {
    NSLog(@"My name is %@ I am %ld years old. my phone number is %@", self.name, self.age, self.phone.phoneNumber);
}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
        Person *p = [[Person alloc] init];
        
        [p setValue:@"Jiaming Chen" forKey:@"name"];
        [p setValue:@22 forKey:@"age"];
        [p setValue:[[Phone alloc] init] forKey:@"phone"];
        [p setValue:@"18666668888" forKeyPath:@"phone.phoneNumber"];
        //输出: My name is Jiaming Chen I am 22 years old. my phone number is 18666668888
        [p showMyself];
        //输出: Name: Jiaming Chen
        NSLog(@"Name: %@", [p valueForKey:@"name"]);
        //输出: Age: 22
        NSLog(@"Age: %@", [p valueForKey:@"age"]);
        //输出: Phone Number: 18666668888
        NSLog(@"Phone Number: %@", [p valueForKeyPath:@"phone.phoneNumber"]);
    }
    return 0;
}

@interface Person : NSObject
{
    @private
    NSString *name;
    NSString *_name;
}

- (void)outputAddress;

@end

@implementation Person
{
    NSInteger age;
}

- (void)outputAddress
{
    NSLog(@"Address name: %p _name: %p", name, _name);
}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
        Person *p = [[Person alloc] init];
        
        [p setValue:@"Jiaming Chen" forKey:@"name"];
        [p setValue:@"CCCC" forKey:@"_name"];
        [p setValue:@22 forKey:@"age"];
        
        //输出: Name: CCCC 0x1000010a8
        NSLog(@"Name: %@ %p", [p valueForKey:@"name"], [p valueForKey:@"name"]);
        //输出: _Name: CCCC 0x1000010a8
        NSLog(@"_Name: %@ %p", [p valueForKey:@"_name"], [p valueForKey:@"_name"]);
        //输出: Age: 22
        NSLog(@"Age: %@", [p valueForKey:@"age"]);
        //输出: Address name: 0x0 _name: 0x1000010a8
        [p outputAddress];

    }
    return 0;
}

#import <Foundation/Foundation.h>
//Person类
@interface Person : NSObject

@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) NSUInteger age;
//服务端为id，由于id是OC的关键字，取名为idNumber
@property (nonatomic, copy) NSString *idNumber;
- (void)showMyself;

@end

@implementation Person

@synthesize name = _name;
@synthesize age = _age;
@synthesize idNumber = _idNumber;

- (void)showMyself {
    NSLog(@"Name: %@ Age: %ld idNumber: %@", self.name, self.age, self.idNumber);
}

- (nullable id)valueForUndefinedKey:(NSString *)key
{
    return nil;
}

- (void)setValue:(nullable id)value forUndefinedKey:(NSString *)key
{
    //如果这个key为id
    if ([key isEqualToString:@"id"])
    {
        //调用setValue:forKey方法为idNumber赋值
        [self setValue:value forKey:@"idNumber"];
    }
}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        //假设为服务端获取的json数据转换的dictionary
        NSDictionary *dict = @{@"name": @"Jiaming Chen", @"age": @20, @"id": @"1603121434"};
        
        Person *p = [[Person alloc] init];
        //遍历上述字典的key
        [dict enumerateKeysAndObjectsUsingBlock:^(id  _Nonnull key, id  _Nonnull obj, BOOL * _Nonnull stop) {
            //直接使用kvc赋值，不需要再写一行一行代码赋值
            [p setValue:obj forKey:key];
        }];
        //输出: Name: Jiaming Chen Age: 20 idNumber: 1603121434
        [p showMyself];
    }
    return 0;
}

- (instancetype)init
{
    if (self=  [super init])
    {
        self.view.backgroundColor = [UIColor whiteColor];
        
        UIView *containerView = [[UIView alloc] initWithFrame:CGRectMake(0, 200, ScreenWidth, 200)];
        containerView.backgroundColor = [UIColor greenColor];
        [self.view addSubview:containerView];
        
        UIPageControl *pageControler = [[UIPageControl alloc] initWithFrame:CGRectMake(0, 180, ScreenWidth, 20)];
        pageControler.numberOfPages = 4;
        [pageControler setPageIndicatorTintColor:[UIColor blueColor]];
        [pageControler setCurrentPageIndicatorTintColor:[UIColor blackColor]];
        [containerView addSubview:pageControler];       
    }
    return self;
}

执行下述代码需要import <objc/runtime.h>头文件

unsigned int count = 0;
//该方法是C函数，获取所有属性
Ivar * ivars = class_copyIvarList([pageControler class], &count);
for (unsigned int i = 0; i < count; i ++) 
{
    Ivar ivar = ivars[i];
    //获取属性名
    const char * name = ivar_getName(ivar);
    //使用KVC直接获取相关属性的值
    NSObject *value = [pageControler valueForKey:[NSString stringWithUTF8String:name]];
    NSLog(@"%s %@", name, value);
}
//需要释放获取到的属性
free(ivars);

输出如下:

_lastUserInterfaceIdiom -1
_indicators (
    "<UIView: 0x100b0d820; frame = (-3.5 -3.5; 7 7); layer = <CALayer: 0x1c4227c00>>",
    "<UIView: 0x100b0da00; frame = (-3.5 -3.5; 7 7); layer = <CALayer: 0x1c4227cc0>>",
    "<UIView: 0x100b0dbe0; frame = (-3.5 -3.5; 7 7); layer = <CALayer: 0x1c4227d20>>",
    "<UIView: 0x100b0ddc0; frame = (-3.5 -3.5; 7 7); layer = <CALayer: 0x1c4227da0>>"
)
_currentPage 0
_displayedPage 0
_pageControlFlags (null)
_currentPageImage (null)
_pageImage (null)
_currentPageImages (null)
_pageImages (null)
_backgroundVisualEffectView (null)
_currentPageIndicatorTintColor UIExtendedGrayColorSpace 0 1
_pageIndicatorTintColor UIExtendedSRGBColorSpace 0 0 1 1
_legibilitySettings (null)
_numberOfPages 4        

[pageControler setValue:[UIImage imageNamed:@"line"] forKeyPath:@"pageImage"];
[pageControler setValue:[UIImage imageNamed:@"current"] forKeyPath:@"currentPageImage"];

#import <Foundation/Foundation.h>

@interface Person : NSObject
//为了方便查看重写的代码将name改成cjmName
@property (nonatomic, copy) NSString *cjmName;
@property (nonatomic, assign) NSUInteger age;
- (void)showMyself;

@end

@implementation Person

@synthesize cjmName = _cjmName;
@synthesize age = _age;

- (void)showMyself {
    NSLog(@"Name: %@ Age: %ld", self.cjmName, self.age);
}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
        Person *p = [[Person alloc] init];
        
        [p setValue:@"Jiaming Chen" forKey:@"cjmName"];
        [p setValue:@22 forKey:@"age"];
        
        p.cjmName = @"CCCC";
        
        [p showMyself];
    }
    return 0;
}

int main(int argc, const char * argv[]) {
    /* @autoreleasepool */ { __AtAutoreleasePool __autoreleasepool;

        Person *p = ((Person *(*)(id, SEL))(void *)objc_msgSend)((id)((Person *(*)(id, SEL))(void *)objc_msgSend)((id)objc_getClass("Person"), sel_registerName("alloc")), sel_registerName("init"));

        ((void (*)(id, SEL, id _Nullable, NSString *))(void *)objc_msgSend)((id)p, sel_registerName("setValue:forKey:"), (id _Nullable)(NSString *)&__NSConstantStringImpl__var_folders_1f_dz4kq57d4b19s4tfmds1mysh0000gn_T_main_080287_mi_1, (NSString *)&__NSConstantStringImpl__var_folders_1f_dz4kq57d4b19s4tfmds1mysh0000gn_T_main_080287_mi_2);
        ((void (*)(id, SEL, id _Nullable, NSString *))(void *)objc_msgSend)((id)p, sel_registerName("setValue:forKey:"), (id _Nullable)((NSNumber *(*)(Class, SEL, int))(void *)objc_msgSend)(objc_getClass("NSNumber"), sel_registerName("numberWithInt:"), 22), (NSString *)&__NSConstantStringImpl__var_folders_1f_dz4kq57d4b19s4tfmds1mysh0000gn_T_main_080287_mi_3);

        ((void (*)(id, SEL, NSString *))(void *)objc_msgSend)((id)p, sel_registerName("setCjmName:"), (NSString *)&__NSConstantStringImpl__var_folders_1f_dz4kq57d4b19s4tfmds1mysh0000gn_T_main_080287_mi_4);

        ((void (*)(id, SEL))(void *)objc_msgSend)((id)p, sel_registerName("showMyself"));
    }
    return 0;
}