NSString issues

I have an NSString that gets assigned a string value. How do I take this NSString and insert @"-thumbnail" between th开发者_运维知识库e file's name and its extension?

In other words, how do I go from:

NSString *fileName = @"myFile.png";

to:

NSString *thumbnailName = [NSString someMagicFunction...]
NSLog(@"%@", thumbnailName);  // Should Output "myFile-thumbnail.png"

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The NSString additions for path components can come in handy, specifically: pathExtension and stringByDeletingPathExtension

Edit: see also: stringByAppendingPathExtension: (as pointed out by Dave DeLong)

NSString * ext = [fileName pathExtension];
NSString * baseName = [fileName stringByDeletingPathExtension];
NSString * thumbBase = [baseName stringByAppendingString:@"-thumbnail"];
NSString * thumbnailName = [thumbBase stringByAppendingPathExtension:ext];

If you really want that magicFunction to exist, you can add a category method to NSString like so:

@interface NSString (MoreMagic)
- (NSString *)stringByAddingFileSuffix:(NSString *)suffix;
@end

@implementation NSString (MoreMagic)
- (NSString *)stringByAddingFileSuffix:(NSString *)suffix
{
    NSString * extension = [self pathExtension];
    NSString * baseName = [self stringByDeletingPathExtension];
    NSString * thumbBase = [baseName stringByAppendingString:suffix];
    return [thumbBase stringByAppendingPathExtension:extension];
}
@end

To be used as follows:

NSString * thumbnailName = [fileName stringByAddingFileSuffix:@"-thumbnail"];

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If you are certain of your filenames, you could also simply do:

[NSString stringByReplacingOccurrencesOfString:@"." withString:@"-thumbnail."]

But the path handling stuff is cleaner (doesn't care how many "." you have in the name) and good to know about for trickier cases.

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We've got an opensource category for just that: -[NSString ks_stringWithPathSuffix:]