KVC KVO 模式

最新推荐文章于 2024-12-03 19:57:14 发布

原创最新推荐文章于 2024-12-03 19:57:14 发布 · 411 阅读

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本文介绍了Objective-C中KVC(key-value coding)的基本使用方法，包括属性的直接赋值，并展示了如何利用KVO(key-value observing)来监听对象属性的变化。

KVC key value coding 相当于OC的类对象 . 语法直接赋值

@interface People : NSObject

@property (nonatomic) int name;
@property (nonatomic) NSString  *nameStr;

@end

 People *p = [[People alloc]init];
    [p setValue:@2 forKey:@"name"];
    [p setValue:@"sdfsdf" forKey:@"nameStr"];

    array = [NSMutableArray new];
    [array addObject:p];
    
    int a = [[p valueForKey:@"name"] intValue];
    NSString *a2 = [p valueForKey:@"nameStr"];

KVO 监听值变化，当监听的key 的 value值变化时，会触发

observeValueForKeyPath

必须是全局变量或者用数组保存局部变量，否则会报错：

An instance 0x60000002f940 of class People was deallocated while key value observers were still registered with it. Current observation info: <NSKeyValueObservationInfo 0x60000002ff00> (
<NSKeyValueObservance 0x60000005e3c0: Observer: 0x7fc3fad0c030, Key path: nameStr, Options: <New: NO, Old: NO, Prior: NO> Context: 0x103cdd298, Property: 0x60000005e450>
)'

static NSString * const KVO_NameStr_CHANGED = @"KVO_CONTEXT_ADDRESS_CHANGED";
[p addObserver:self forKeyPath:@"nameStr" options:0 context:(__bridge void * _Nullable)(KVO_NameStr_CHANGED)];

-(void)dealloc
{
    People *p = [array objectAtIndex:0];
    [p removeObserver:self forKeyPath:KVO_NameStr_CHANGED];
    
}

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context
{
    if (context == (__bridge void * _Nullable)(KVO_NameStr_CHANGED))
    {
        NSLog(@"%@",[object valueForKey:@"nameStr"]);
    }
}

-(void)buttonClickToChangKVO
{
//    p.nameStr = @"200";
    People *p = [array objectAtIndex:0];
    p.nameStr = @"200";

}