iphone - 移除行为异常的 objectAtIndex

Question

嗨，我有一个数组数组，我在添加某个索引后删除了一个对象。不知何故，我认为这表现得很奇怪，或者我可能忽略了一些事情。这是代码。我用 nslogs 对其进行跟踪。

    for (int i = 0; i < easyQuestionsLength; i++) {
    NSMutableArray *questionSet = [easyQuestions objectAtIndex:i];
    for(int j = 0; j < [[easyQuestionsVariant objectAtIndex:i] count]; j++)
    {
        NSArray *variant = [[easyQuestionsVariant objectAtIndex:i] objectAtIndex:j];
        NSLog(@"questionSet b4 %@",questionSet);

        [questionSet insertObject:variant atIndex:7];
        NSLog(@"questionSet aft ins%@",questionSet);

        [questionsArray addObject:questionSet];
        NSLog(@"questionsArray aft add %@",questionsArray);

        [questionSet removeObjectAtIndex:7];
        NSLog(@"questionsArray aft rem %@",questionsArray);

        easyQCtr++;
    }
}

这是调试控制台输出:

2011-09-06 16:17:33.498 EasyQuiz[25584:10d03] questionSet b4 (
0,
1,
14,
"[1] The value of the digit {#} in {#} is __________.",
none,
2,
1
)
2011-09-06 16:17:33.499 EasyQuiz[25584:10d03] questionSet aft (
0,
1,
14,
"[1] The value of the digit {#} in {#} is __________.",
none,
2,
1,
    {
    choice =         (
        70000,
        7000,
        700,
        70
    );
    var =         (
        7,
        70348
    );
}
)
2011-09-06 16:17:33.500 EasyQuiz[25584:10d03] questionsArray aft add (
    (
    0,
    1,
    14,
    "[1] The value of the digit {#} in {#} is __________.",
    none,
    2,
    1,
            {
        choice =             (
            70000,
            7000,
            700,
            70
        );
        var =             (
            7,
            70348
        );
    }
)
)
2011-09-06 16:17:33.500 EasyQuiz[25584:10d03] questionsArray aft rem (
    (
    0,
    1,
    14,
    "[1] The value of the digit {#} in {#} is __________.",
    none,
    2,
    1
)
)

我只是在这里做一个 removeObjectAtIndex [questionSet removeObjectAtIndex:7];但为什么还要从 questionsArray 中删除？我完全迷失在这里。我知道这是逻辑错误，但我似乎找不到问题所在。 :D

Answer 1

questionsArray 是一个数组，数组不包含对象，它们只包含指向真实数据的指针。因此，如果您向数组添加一个项目，不会进行任何复制，只会存储指向原始对象的指针并保留该对象。

您向questionsArray 添加了一个数组对象，但这只是一个新引用。如果您想存储副本，则必须执行以下操作:

[questionsArray addObject: [questionSet copy]];

更新

FWIW、questionSet 和 questionsArray 绝对不会指向同一个对象。这可以在您获得的显示器中看到

questionSet 显示为

(               --> questionSet, containing:
  0,
  1,
  14,
  ...
)

而 questionsArray 显示为

(               --> questionsArray, containing:
  (             --> questionSet (only element of questionsArray), containing:
    0,
    1,
    14,
    ...
  )
)

这表明questionsArray 包含一个对象questionSet。事实上，您可以从 questionSet 中删除某些内容并将其显示在 questionsArray 中，反之亦然，因为 questionsArray 仅包含一个 对 的引用和不是 questionSet 的副本，并且该描述递归地显示了的所有元素包含数组、集合和字典。

看看这个简单的代码:

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{

    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    NSMutableArray *deeplyNested = [NSMutableArray arrayWithObjects: @"one", @"two", @"three", nil];
    NSArray *toplevel = [NSArray arrayWithObject: [NSArray arrayWithObject: deeplyNested]];

    NSLog(@"\n%@", toplevel);

    [[[toplevel lastObject] lastObject] removeObjectAtIndex: 1];
    [deeplyNested addObject: @"thousand"];

    NSLog(@"\n%@", toplevel);

    [pool drain];
    return 0;
}

输出是:

2011-09-06 12:36:44.966 NestedArrays[12553:707] 
(
    (
        (
            one,
            two,
            three
        )
    )
)
2011-09-06 12:36:44.968 NestedArrays[12553:707] 
(
    (
        (
            one,
            three,
            thousand
        )
    )
)

如您所见，deeplyNested 可以通过 [[toplevel lastObject] lastObject] 或直接访问。结果是一样的，因为它们引用了同一个对象。