NSArray的containsObject方法 [英] NSArray containsObject method

问题描述

我有作为X code编码一个简单的问题，但不知道为什么事情都没有执行，因为我认为。我有对象（自定义对象）的数组。我只是想检查，如果这个人是在阵列​​内。我用下面的code：

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积极的结果，但事实并非如此。此外，我检查创建的对象是否是相同的。

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，这是我得到了什么：

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 是内部集合阵列，但没有显示出来，当我使用 containsObject：进行检查。任何人都可以给我一些指导，我哪一部分错了吗？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

有关文档<一个href=\"http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Classes/NSArray_Class/NSArray.html#//apple_ref/occ/instm/NSArray/containsObject:\"相对=nofollow> [NSArray的containsObject：] 说：

The documentation for [NSArray containsObject:] says:

此方法确定是否
  anObject是通过在接收机present
  发送isEqual：方法判断消息给每个
  接收器的对象（和传球
  anObject作为参数到每个
  isEqual：方法：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).

问题是，你要比较的对象引用，而不是对象的值。为了使这个具体的例子工作，你要么需要发送 [收藏containsObject：] 它包含一个变量的一个实例（如 A ， B 或 C ），否则你将需要重写<一个href=\"http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Protocols/NSObject_Protocol/Reference/NSObject.html#//apple_ref/occ/intfm/NSObject/isEqual:\"相对=nofollow> [NSObject的isEqual：方法判断。 在项目类方法

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.

这是你的的isEqual 方法可能是什么样子：

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，你可能想看看这个<一个href=\"http://stackoverflow.com/questions/254281/best-practices-for-overriding-isequal-and-hash\">question.

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