NSMutableDictionary的深度可变副本 [英] deep mutable copy of a NSMutableDictionary

问题描述

我正在尝试创建NSMutableDictionary的深层副本并将其分配给另一个NSMutableDictionary。字典包含一堆数组，每个数组包含名称，键是字母表（这些名称的第一个字母）。因此字典中的一个条目是'A' - >'Adam'，'Apple'。这是我在书中看到的，但我不确定它是否有效：

I am trying to create a deep-copy of a NSMutableDictionary and assign it to another NSMutableDictionary. The dictionary contains a bunch of arrays, each array containing names, and the key is an alphabet (the first letter of those names). So one entry in the dictionary is 'A' -> 'Adam', 'Apple'. Here's what I saw in a book, but I'm not sure if it works:

- (NSMutableDictionary *) mutableDeepCopy
{
    NSMutableDictionary * ret = [[NSMutableDictionary alloc] initWithCapacity: [self count]];
    NSArray *keys = [self allKeys];

    for (id key in keys)
    {
        id oneValue = [self valueForKey:key]; // should return the array
        id oneCopy = nil;

        if ([oneValue respondsToSelector: @selector(mutableDeepCopy)])
        {
            oneCopy = [oneValue mutableDeepCopy];
        }
        if ([oneValue respondsToSelector:@selector(mutableCopy)])
        {
            oneCopy = [oneValue mutableCopy];
        }

        if (oneCopy == nil) // not sure if this is needed
        {   
            oneCopy = [oneValue copy];
        }
        [ret setValue:oneCopy forKey:key];

        //[oneCopy release];
    }
    return ret;
}

• 如果[onecopy release]存在或者不是吗？



• 以下是我将如何调用此方法：

  • should the [onecopy release] be there or not?

  • Here's how I'm going to call this method:

    self。 namesForAlphabets = [self.allNames mutableDeepCopy];

    这样可以吗？还是会导致泄漏？ （假设我将self.namesForAlphabets声明为属性，并在dealloc中释放它）。

    Will that be ok? Or will it cause a leak? (assume that I declare self.namesForAlphabets as a property, and release it in dealloc).

    推荐答案

    重要：问题（以及我的代码）都涉及一个非常具体的案例，其中NSMutableDictionary包含仅字符串数组。对于更复杂的示例，这些解决方案将不起作用。有关更一般的案例解决方案，请参阅以下内容：

    IMPORTANT: The question (and my code below) both deal with a very specific case, in which the NSMutableDictionary contains only arrays of strings. These solutions will not work for more complex examples. For more general case solutions, see the following:

    
    
    • Tom Dalling的回答
    
    
    • dreamlax的回答
    
    
    • 来自yfujiki的GitHub Gist来源
    
    
    • Tom Dalling's answer
    • dreamlax's answer
    • Source from yfujiki on GitHub Gist

    这个具体案例的答案：

    您的代码应该可以使用，但您肯定需要 [oneCopy release] 。当您使用 setValue：forKey 添加复制对象时，新词典将保留复制的对象，因此如果您不调用 [oneCopy release] ，所有这些对象都会被保留两次。

    Your code should work, but you will definitely need the [oneCopy release]. The new dictionary will retain the copied objects when you add them with setValue:forKey, so if you do not call [oneCopy release], all of those objects will be retained twice.

    一个好的经验法则：如果你 alloc ，保留或复制的东西，你还必须发布它。

    A good rule of thumb: if you alloc, retain or copy something, you must also release it.

    注意：这里有一些示例代码仅适用于某些情况的 。这是有效的，因为你的NSMutableDictionary只包含字符串数组（不需要进一步深度复制）：

    Note: here is some sample code that would work for certain cases only. This works because your NSMutableDictionary contains only arrays of strings (no further deep copying required):

    - (NSMutableDictionary *)mutableDeepCopy
    {
        NSMutableDictionary * ret = [[NSMutableDictionary alloc]
                                      initWithCapacity:[self count]];
    
        NSMutableArray * array;
    
        for (id key in [self allKeys])
        {
            array = [(NSArray *)[self objectForKey:key] mutableCopy];
            [ret setValue:array forKey:key];
            [array release];
        }
    
        return ret;
    }
    

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