KVO 是 Key-Value Observer 键值观察
参数介绍: self.myLabel 被监听对象
Observer: 监听的属性值发生变化时，被通知的对象
forKeyPath:被监听的属性
option:观察情况的设置，NSKeyValueObservingOptionNew 回调的方法中给的信息，只有新值 NSKeyValueObservingOptionOld 回调方法中携带旧值
context:上下文
[self.myLabel addObserver:self forKeyPath:@"text" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];
当监听的对象的被监听属性，发生变化时会调用这个方法，KVO的回调方法
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
{
//keyPath:被监听的属性
//object:被监听的对象
//change:发生改变的信息
//context 上下文
if ([keyPath isEqualToString:@"text"]) {
NSLog(@"%@",change);
NSLog(@"old = %@",change[@"old"]);
}
}
点击按钮是触发方法
- (IBAction)addCount:(id)sender
{
self.myLabel.text = [NSString stringWithFormat:@"点击%ld次",++_count];
}
KVC
首先创建两个类(PersonModel和 DogModel),里面的代码如下:
DogModel.h文件
#import <Foundation/Foundation.h>
@interface DogModel : NSObject
/**
狗名
*/
@property (nonatomic, strong) NSString * dogName;
@end
DogModel.m文件
#import "DogModel.h"
@implementation DogModel
@end
PersonModel.h文件
#import <Foundation/Foundation.h>
@class DogModel;
@interface PersonModel : NSObject
/**
人名
*/
@property (nonatomic, strong) NSString * name;
/**
年龄
*/
@property (nonatomic, assign) NSInteger age;
/**
人有一条狗
*/
@property (nonatomic, strong) DogModel * dog;
- (void)logNum;
@end
PersonModel.m文件
#import "PersonModel.h"
@implementation PersonModel{
NSInteger _num; // 私有属性
}
- (instancetype)init{
if (self = [super init]) {
_num = 9; // 给一个初始值
}
return self;
}
- (void)logNum{
NSLog(@"personModel->num:%zd",_num);
}
@end
//1. 简单使用
PersonModel *personModel = [[PersonModel alloc]init];
personModel.name = @"梅西";
[personModel setValue:@"16" forKeyPath:@"age"];
//[personModel setValue:@"88" forKeyPath:@"num"]; // 使用KVC赋值,如果这个类没有这个属性,则会崩溃
NSLog(@"personModel->name:%@,personModel->age:%zd",personModel.name,personModel.age);
打印结果
没有num属性赋值时
打印结果.png
有
num属性赋值时
有num属性.png
注意:使用setValue: forKeyPath:赋值时,一定确保类拥有这个属性,否则会崩溃
//2. 综合赋值
PersonModel *personModel = [[PersonModel alloc]init];
personModel.dog = [[DogModel alloc]init];
personModel.name = @"梅西";
[personModel setValue:@"16" forKeyPath:@"age"];
[personModel setValue:@"Jack" forKeyPath:@"dog.dogName"]; // 使用forKeyPath: 可以索引给属性赋值
NSLog(@"personModel->name:%@,personModel->age:%zd,狗名字->dogName:%@",personModel.name,personModel.age,personModel.dog.dogName);
注意:forKeyPath: 和 forKey: 功能是一样的,但是forKeyPath:可以进行索引赋值,所以以后尽量使用forKeyPath:
综合赋值.png
//3. 改变一个类的私有属性值(重要)
PersonModel *personModel = [[PersonModel alloc]init];
[personModel setValue:@"88" forKeyPath:@"_num"]; // num _num
[personModel logNum];
改变类的私有属性值.png
//4. 字典转模型
//5. 取值操作
//6. 模型转字典
PersonModel *personModel = [[PersonModel alloc]init];
personModel.name = @"梅西";
[personModel setValue:@"16" forKeyPath:@"age"];
NSDictionary *dict = [personModel dictionaryWithValuesForKeys:@[@"name",@"age"]];
NSLog(@"%@",dict);
//7. 取出数组中所有Model的某个属性值
PersonModel *per1 = [[PersonModel alloc]init];
per1.name = @"A";
per1.age = 12;
PersonModel *per2 = [[PersonModel alloc]init];
per2.name = @"B";
per2.age = 13;
PersonModel *per3 = [[PersonModel alloc]init];
per3.name = @"C";
per3.age = 14;
NSArray *perArr = @[per1,per2,per3];
NSArray *nameArr = [perArr valueForKeyPath:@"name"];
NSLog(@"nameArr:%@",nameArr);
取出数组中所有Model的某个属性值.png
