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不执行，我认为。我有一个对象数组（自定义对象）。我只想检查这是否是在数组内。我使用下面的代码：

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");
}

我想上面的检查会给我一个肯定的结果，但它不是。此外，我检查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 在集合数组内，但是当我使用 来检查它。任何人都可以给我一些方向，哪一部分我错了？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：

此方法确定
anObject是否存在于接收者
发送一个isEqual：消息给每个
接收者的对象（并传递
anObject作为参数到每个
isEqual：message）。

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).

问题是你正在比较对象的引用，而不是对象的值。为了使这个具体的例子工作，你将需要发送 [collection containsObject：] 它包含的变量的实例（例如 A ， B 或 C ），否则您将需要覆盖 Item 类中的 [NSObject isEqual：] 方法。

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.

这是您的 isEqual 方法可能如下所示：

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，你可能想看看查询。

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

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