objective-c 如何动态填充 NSArray？
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How can I fill an NSArray dynamically?
提问by Thanks
I have a forloop. Inside that loop I want to fill up an NSArraywith some objects. But I don't see any method that would let me do that. I know in advance how many objects there are. I want to avoid an NSMutableArray, since some people told me that's a very big overhead and performance-brake compared to NSArray.
我有一个for循环。在那个循环中，我想NSArray用一些对象填充一个。但我没有看到任何方法可以让我这样做。我事先知道有多少对象。我想避免NSMutableArray，因为有些人告诉我，与NSArray.
I've got something like this:
我有这样的事情：
NSArray *returnArray = [[NSArray alloc] init];
for (imageName in imageArray) {
UIImage *image = [UIImage imageNamed:imageName];
//Now, here I'd like to add that image to the array...
}
I looked in the documentation for NSArray, but how do I specify how many elements are going to be in there? Or must I really use NSMutableArrayfor that?
我查看了 的文档NSArray，但是如何指定其中将包含多少个元素？或者我真的必须使用NSMutableArray它？
回答by Alnitak
Yes, you need to use an NSMutableArray:
是的，您需要使用一个NSMutableArray：
int count = [imageArray count];
NSMutableArray *returnArray = [[NSMutableArray alloc] initWithCapacity:count];
for (imageName in imageArray) {
UIImage *image = [UIImage imageNamed:imageName];
[returnArray addObject: image];
...
}
EDIT - declaration fixed
编辑 - 声明已修复
回答by Kris
You'll need to use an NSMutableArrayfor that because adding is mutation and NSArrayis immutable.
您需要为此使用NSMutableArray，因为添加是变异，而NSArray是不可变的。
You could make a populated NSMutableArrayinto an NSArrayafterwards (see here for a discussion) but you won't be adding items to a regular old NSArrayanytime soon.
您可以将 a 填充NSMutableArray到NSArrayafter （请参阅此处的讨论），但您不会NSArray很快将项目添加到常规旧的。
回答by Wally Lawless
Would this be a good time to use an NSMutableArray?
这是使用NSMutableArray的好时机吗？
I know you mentioned that you would like to avoid it, but sometimes there's a reason for things like this.
我知道你提到过你想避免它，但有时这样的事情是有原因的。
回答by Rog
I would advise optimising only when you know NSMutableArrayiscausing you a performance hit but if it is, you can always create a static aray from a mutable array after you have populated it. It depends on if the performance hit is caused by you subsequent use of the NSMutableArrayor just by creating it.
我建议仅在您知道NSMutableArray会导致性能下降时进行优化，但如果是，您始终可以在填充可变数组后从可变数组创建静态数组。这取决于性能下降是由您随后使用NSMutableArray还是仅通过创建它引起的。
My guess is that this isn't going to be the performance bottleneck on your app.
我的猜测是这不会成为您应用程序的性能瓶颈。
