NSArray containsObject 方法 [英] NSArray containsObject method

问题描述

我有一个关于 xcode 编码的简单问题，但不知道为什么事情没有像我想象的那样执行.我有一组对象(自定义对象).我只想检查这个是否在数组中.我使用了以下代码:

I have a simple question regarding xcode coding but don't know why things are not performing as I think. I have an array of objects (custom objects). I just want to check if this one is within the array. I used the following code:

NSArray *collection = [[NSArray alloc] initWithObjects:A, B, C, nil]; //A, B, C are custom "Item" objects
Item *tempItem = [[Item alloc] initWithLength:1 width:2 height:3];  //3 instance variables in "Item" objects
if([collection containsObject:tempItem]) {
    NSLog(@"collection contains this item");
}

我想上述检查会给我一个积极的结果，但事实并非如此.进一步，我检查了创建的对象是否相同.

I suppose the above checking will give me a positive result but it's not. Further, I checked whether the objects created are the same.

NSLog(@"L:%i W:%i H:%i", itemToCheck.length, itemToCheck.width, itemToCheck.height);
for (int i = 0, i < [collection count], i++) {
    Item *itemInArray = [collection objectAtIndex:i];
    NSLog(@"collection contains L:%i W:%i H:%i", itemInArray.length, itemInArray.width, itemInArrayheight);
}

在控制台中，这是我得到的:

In the console, this is what I got:

L:1 W:2 H:3
collection contains L:0 W:0 H:0
collection contains L:1 W:2 H:3
collection contains L:6 W:8 H:2

显然 tempItem 位于 collection 数组内，但是当我使用 containsObject: 来检查它时，没有任何显示.谁能给我一些指导，我错了哪一部分?非常感谢！

Obviously the tempItem is inside the collection array but nothing shows up when I use containsObject: to check it. Could anyone give me some direction which part I am wrong? Thanks a lot!

推荐答案

[NSArray containsObject:] 说:

这个方法判断是否anObject 存在于接收器中向每个人发送 isEqual: 消息接收者的对象(和传递anObject 作为参数给每个isEqual: 消息).

This method determines whether anObject is present in the receiver by sending an isEqual: message to each of the receiver’s objects (and passing anObject as the parameter to each isEqual: message).

问题在于您正在比较对象的引用而不是对象的值.为了使这个特定的示例工作，您需要向 [collection containsObject:] 发送它包含的变量的实例(例如 A、B> 或 C)，否则您将需要覆盖 [NSObject isEqual:] 在您的 Item 中的方法 类.

The problem is that you are comparing references to objects rather than the values of the objects. To make this specific example work, you will either need to send [collection containsObject:] an instance of a variable it contains (e.g. A, B, or C), or you will need to override the [NSObject isEqual:] method in your Item class.

这就是你的 isEqual 方法的样子:

This is what your isEqual method might look like:

- (BOOL)isEqual:(id)other {
    if (other == self)
      return YES;
    if (!other || ![other isKindOfClass:[self class]])
      return NO;
    if (self.length != other.length || self.width != other.width || self.height != other.height)
      return NO;
    return YES;
}

为了更好的实现，您可能需要查看这个问题.

For a better implementation, you may want to look at this question.

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