IOS : NSString retrieving a substring from a string - iphone

Question

Hey I am looking for a way to extract a string from another string. It could be any length and be in any part of the string so the usual methods don't work.
For example
http://bla.com/bla?id=%1234%&something=%888%
What I want to extract is from id=% to the next %.
Any idea's?

Answer 1

Use the rangeOfString method:
NSRange range = [string rangeOfString:#"id=%"];
if (range.location != NSNotFound)
{
//range.location is start of substring
//range.length is length of substring
}
You can then chop up the string using the substringWithRange:, substringFromIndex: and substringToIndex: methods to get the bits you want. Here's a solution to your specific problem:
NSString *param = nil;
NSRange start = [string rangeOfString:#"id=%"];
if (start.location != NSNotFound)
{
param = [string substringFromIndex:start.location + start.length];
NSRange end = [param rangeOfString:#"%"];
if (end.location != NSNotFound)
{
param = [param substringToIndex:end.location];
}
}
//param now contains your value (or nil if not found)
Alternatively, here's a general solution for extracting query parameters from a URL, which may be more useful if you need to do this several times:
- (NSDictionary *)URLQueryParameters:(NSURL *)URL
{
NSString *queryString = [URL query];
NSMutableDictionary *result = [NSMutableDictionary dictionary];
NSArray *parameters = [queryString componentsSeparatedByString:#"&"];
for (NSString *parameter in parameters)
{
NSArray *parts = [parameter componentsSeparatedByString:#"="];
if ([parts count] > 1)
{
NSString *key = [parts[0] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSString *value = [parts[1] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
result[key] = value;
}
}
return result;
}
This doesn't strip the % characters from the values, but you can do that either with
NSString *value = [[value substringToIndex:[value length] - 1] substringFromIndex:1];
Or with something like
NSString *value = [value stringByReplacingOccurencesOfString:#"%" withString:#""];
UPDATE: As of iOS 8+ theres a built-in class called NSURLComponents that can automatically parse query parameters for you (NSURLComponents is available on iOS 7+, but the query parameter parsing feature isn't).

Answer 2

Try this
NSArray* foo = [#"10/04/2011" componentsSeparatedByString: #"/"];
NSString* day = [foo objectAtIndex: 0];