键值 - 观察Cocoa中的to-many关系

Question

我正在尝试使用键值观察来为NSMutableArray工作.下面是MyObservee的.h文件,观察到的类:

@interface MyObservee : NSObject {
    @private int someValue;
    @private NSMutableArray *someArray;
}

@property (readwrite,assign) int someValue;
- (NSMutableArray *)someArray;
@end

MyObserver类实现observeValueForKeyPath:ofObject:change:context:.这是我添加观察者的方式:

MyObservee *moe = [[MyObservee alloc] init];
MyObserver *mobs = [[MyObserver alloc] init];

[moe addObserver:mobs 
      forKeyPath:@"someArray" 
         options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld) 
         context:NULL];

[moe.someArray addObject:@"hi there"];

为什么addObject:message不会作为someArray键路径的更改而触发？我觉得这里有一些我不完全理解的东西.

Answer 1

您需要实现KVC编程指南中定义的索引数组访问器.然后,您必须使用这些访问器来访问阵列,KVO触发将起作用.您还可以调用-mutableArrayValueForKey:并将该数组用于addObject:等等,它将依次调用访问器方法,并且也会发生KVO触发.还有用于NSSets的设置访问器,请参见此处和此处.

例:

@interface MyClass : NSObject
{
    NSMutableArray *_orders;
}

@property(retain) NSMutableArray *orders;

- (NSUInteger)countOfOrders;
- (id)objectInOrdersAtIndex:(NSUInteger)index;
- (void)insertObject:(id)obj inOrdersAtIndex:(NSUInteger)index;
- (void)removeObjectFromOrdersAtIndex:(NSUInteger)index;
- (void)replaceObjectInOrdersAtIndex:(NSUInteger)index withObject:(id)obj;


@end