iOS NSSet / NSArray / NSDictionary有多大？

Question

I feel I should first describe what I'm trying to do and then I'll ask my question(s).

Background

I have a large amount of words (could be up to 5,000). I want to be able to display a random 3 of these words on the screen and when the user presses a button, it will display another 3 random words, but without duplicates (ie without presenting the same word to the user again). This will loop until a timer runs out.

Possible solution

If the number of words was less, I'd just add these into an NSMutableSet, use -anyObject 3 times to get the words, and then remove the 3 words from the set each time so they're not used again when I next call -anyObject. The problem with this is I don't know if I can have a set with 5,000 NSStrings in it in iOS.

Question

So my questions are

1. Can I have a collection object (NSSet, NSArray, NSDictionary) with about 5,000 strings in it in iOS without any performance problems?
2. If not how would I go about reading a subset of strings from a file to get an acceptable array size and then pull out more when I've emptied that array?
3. What would be the best way to store these strings? They're only words, so not very long ones. I was thinking of just adding them to a file with a string on each line and reading them into a collection object on application load.

Thanks in advance.

Answer 1

Just to have an idea of which memory dimensions we are looking at: 5000 words of 8 letters each can be represented in UTF-8 (8 bits per letter) with

5000 * 8 * 8 = 320,000 bits = 40,000 bytes < 40 kB

Even if the overhead of a NSArray , NSSet etc. would double or triple that size (which it certainly doesn't), you'd be fine. An iPhone 4S has a RAM size of 1 GB, that's 1,048,576 kB, several ten thousand times the size of your object. In short: Don't worry.

You could store your words in a text file, separated by spaces, and simply read them into an NSArray with

NSArray *testArray = [stringOfTextfileContent componentsSeparatedByString:@" "];

Answer 2

限制取决于您可用的内存量。