KVC和KVO

KVC取值 -- valueForKeyPath

// XMGBook.h
#import <Foundation/Foundation.h>

@interface XMGBook : NSObject

@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) double price;

@end

// XMGBook.m
#import "XMGBook.h"

@implementation XMGBook

@end

// main.m
#import <Foundation/Foundation.h>
#import "XMGBook.h"


int main(int argc, const char * argv[]) {

    XMGBook *book1 = [[XMGBook alloc] init];
    book1.name = @"123";
    book1.price = 20.5;

    XMGBook *book2 = [[XMGBook alloc] init];
    book2.name = @"345";
    book2.price = 30.5;

    XMGBook *book3 = [[XMGBook alloc] init];
    book3.name = @"678";
    book3.price = 40.5;

    NSArray *books = @[book1, book2, book3];

    // 如果valueForKeyPath:方法的调用者是数组，那么就是去访问数组元素的属性值
    // 取得books数组中所有XMGBook对象的name属性值，放在一个新的数组中返回
    NSArray *names = [books valueForKeyPath:@"name"];

    NSLog(@"%@", names);

//    XMGPerson *p = [[XMGPerson alloc] init];
//    p.books = @[book1, book2, book3];
//
//    NSLog(@"%@", [p.books valueForKeyPath:@"@count"]);
//    NSLog(@"%@", [p valueForKeyPath:@"books.@count"]);
//
//    NSLog(@"%@", [p.books valueForKeyPath:@"@avg.price"]);
//    NSLog(@"%@", [p valueForKeyPath:@"books.@avg.price"]);
//
//    NSLog(@"%@", [p.books valueForKeyPath:@"@max.price"]);
//    NSLog(@"%@", [p valueForKeyPath:@"books.@max.price"]);
//
//    NSLog(@"%@", [p.books valueForKeyPath:@"@min.price"]);
//    NSLog(@"%@", [p valueForKeyPath:@"books.@min.price"]);

    return 0;
}

输出结果图:

// XMGPerson.h
#import <Foundation/Foundation.h>

@interface XMGPerson : NSObject

@property (nonatomic, strong) NSString *name;
@property (nonatomic, assign) double money;

@end

// XMGPerson.m
#import "XMGPerson.h"

@implementation XMGPerson

@end

// main.m
#import <Foundation/Foundation.h>
#import "XMGPerson.h"


int main(int argc, const char * argv[]) {

    XMGPerson *person = [[XMGPerson alloc] init];
    person.name = @"abc";
    person.money = 9.9;

    NSLog(@"%@,%@", [person valueForKeyPath:@"name"], [person valueForKeyPath:@"money"]);


    return 0;
}

效果图:

KVC

• 全称:Key Value Coding(键值编码)
• 赋值

// 能够修改私有成员变量
[p setValue:<#(nullable id)#> forKey:<#(nonnull NSString *)#>];
[p setValue:<#(nullable id)#> forKeyPath:<#(nonnull NSString *)#>];
[p setValuesForKeysWithDictionary:(nonnull NSDictionary<NSString *,id> *)];

• 取值

// 能够取得私有成员变量
[p valueForKey:<#(nonnull NSString *)#>];
[p valueForKeyPath:<#(nonnull NSString *)#>];
[p dictionaryWithValuesForKeys:<#(nonnull NSArray<NSString *> *)#>];

• KVO

/*
  KVO: Key Value Observing (键值监听)
  作用: 监听对象的属性值发生改变, 通知给监听者
 */
#import "ViewController.h"
#import "XMGPerson.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    XMGPerson *person = [[XMGPerson alloc] init];
    person.name = @"zhangsan";

    // 为对象p添加一个观察者(监听器)
    // Observer 观察者(监听器)
    // KeyPath 键 ---> name （或者可以这样理解:属性名:需要监听哪个属性）
    // options 返回给监听者旧值或者新值
    [person addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionOld  context:nil];
//    [person addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];


    person.name = @"lisi";

    // 释放
//    [person removeObserver:self forKeyPath:@"name"];
    [person removeObserver:self forKeyPath:@"name"];

}

// 应用场景很少，可能就是做彩票那里用到
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
{
    NSLog(@"%@-----%@-----%@",keyPath, object, change);
    NSLog(@"%s", __func__);
}


//- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context{
//    NSLog(@"%@-----%@-----%@",keyPath, object, change);
//    if([keyPath isEqualToString:@"name"]){
//      // ...业务逻辑
//    }else if ([keyPath isEqualToString:@"height"]){
//      // ...业务逻辑
//    }
//}

• KVO

• 全称: Key Value Observing(键值监听)

• 作用:监听模型的属性值改变

• 步骤

  • 添加监听器

  // 利用b对象来监听a对象name属性的改变
  [a addObserver:b forKeyPath:@"name" options:NSKeyValueObservingOptionOld  context:@"test"];
  

  • 在监听器中实现监听方法

  -(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
  

{
NSLog(@"%@-----%@-----%@------%@",keyPath, object, changem, text);
NSLog(@"%s", func);
}