ios - 如何制作一种检测变量是否更改的方法？

Question

我在h文件中声明了@property (strong, nonatomic) NSString *data;，然后将另一个类的NSString传递给“数据”。我想检测“数据”是否已更新，所以我尝试了下面的代码，但它不起作用。

-(void)didChangeValueForKey:(NSString *)key {  

    [super didChangeValueForKey:key];
    if ( [key isEqualToString:@"data"] ) {
        // do something     
    }
}

有人知道如何解决吗？

谢谢你，抱歉我的英语。

Answer 1

为此，可以使用键值观察。

假设您有一个带有属性myObject的对象data，那么您可以执行以下操作...

[self.myObject addObserver:self forKeyPath:@"data" options:NSKeyValueObservingOptionNew context:nil];

然后你有方法...

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    // if you observer multiple properties then they will all fire this method
    // so you need to determine that the right property is being observed

    if (object == self.myObject
        && [keyPath isEqualToString:@"data"]) {
        // if you are here then you know the object that changed is myObject
        // and the property is the data property.

        id theNewData = change[NSKeyValueChangeNewKey];
        // this is the new state of the data
        // you can also get the old state by using different options when adding the observer.
    }
}

您可以阅读有关它的更多信息in the Apple documentation about KVO