KVC赋值的顺序

验证

#import <Foundation/Foundation.h>

@interface MZPerson : NSObject
{
    @public
    int age;
    int isAge;
    int _isAge;
    int _age;
}

@end

@implementation MZPerson

//- (void)setAge:(int)age {
//    NSLog(@"setAge: - %d", age);
//}
//
//- (void)_setAge:(int)age {
//    NSLog(@"_setAge: - %d", age);
//}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        MZPerson *person = [[MZPerson alloc] init];
        [person setValue:@12 forKey:@"age"];
        NSLog(@"世界一盘棋, ZM大博弈.");
    }
    return 0;
}

在注释掉两个set方法，验证成员属性赋值的时候，可以通过断点来验证，如下图所示。

需要特别注意的是：KVC的赋值会出发KVO，可能的原因是，KVO生成了一个子类，并且在赋值前后分别调用了 willChangeValueForKey: 和 didChangeValueForKey:。

- (void)setName:(NSString *)name {
    [self willChangeValueForKey:name];
    [super setName:name];
    [self didChangeValueForKey:name];
}
//或
[self willChangeValueForKey:_name];
_name = newValue;
[self didChangeValueForKey:_name];

KVC的取值顺序

验证

#import <Foundation/Foundation.h>

@interface MZPerson : NSObject
{
    @public
//    int _age;
    int _isAge;
    int age;
    int isAge;
}
@end

@implementation MZPerson

- (instancetype)init {
    if (self = [super init]) {
//        _age = 1;
        _isAge = 2;
        age = 3;
        isAge = 4;
    }
    return self;
}

//- (int)getAge {
//    return 11;
//}

//- (int)age {
//    return 12;
//}

//- (int)isAge {
//    return 13;
//}

//- (int)_age {
//    return 14;
//}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        MZPerson *person = [[MZPerson alloc] init];
        int intValue = [[person valueForKey:@"age"] intValue];
        NSLog(@"%d", intValue);
    }
    return 0;
}