在自定义类上实现 NSFastEnumeration [英] Implementing NSFastEnumeration on Custom Class

问题描述

我有一个继承自 NSObject 的类.它使用 NSMutableArray 来保存子对象，例如人们使用 NSMutableArray *items 来保存 Person 对象.如何在项目上实现 NSFastEnumerator?

I have a class that inherits from NSObject. It uses an NSMutableArray to hold children objects, e.g. People using NSMutableArray *items to hold Person objects. How do I implement the NSFastEnumerator on items?

我尝试了以下但无效:

@interface People : NSObject <NSFastEnumeration>
{
    NSMutableArray *items;
}

@implementation ...

@implementation ...

- (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *)state objects:(id *)stackbuf count:(NSUInteger)len
{
    if(state->state == 0)
    {
        state->mutationsPtr = (unsigned long *)self;
        state->itemsPtr = items;
        state->state = [items count];
        return count;
    }
    else
        return 0;
}

推荐答案

您没有正确使用 NSFastEnumerationState 结构.请参阅 NSFastEnumeration 协议参考并查看在常量部分查看每个字段的描述.在您的情况下，您应该将 state->mutationsPtr 保留为 nil.state->itemsPtr 应该设置为对象的 C 数组，而不是 NSArray 或 NSMutableArray.您还需要将相同的对象放入作为 stackbuf 传递的数组中.

You are not using the NSFastEnumerationState structure properly. See NSFastEnumeration Protocol Reference and look at the constants section to see a description of each of the fields. In your case, you should leave state->mutationsPtr as nil. state->itemsPtr should be set to a C-array of the objects, not an NSArray or NSMutableArray. You also need to put the same objects into the array passed as stackbuf.

但是，由于您使用 NSMutableArray 来包含您正在枚举的对象，您可以将调用转发到该对象:

However, since you are using an NSMutableArray to contain the objects you are enumerating, you could just forward the call to that object:

- (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *)state objects:(id *)stackbuf count:(NSUInteger)len {
    return [items countByEnumeratingWithState:state objects:stackbuf count:len];
}

这篇关于在自定义类上实现 NSFastEnumeration的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！