What is the best practic using url string with NSString stringWithFormat

Question

I use NSString stringWithFormat method for create an URL string. But now I have problem with a "quick" editing this string.

For example I have an script on the server that process some request with parameters.

I have an URL string like this:

http://www.domain.com/api/?param1=%@&param2=%@&param3=%@&param4=%@&param5=%@&

but when I have more than 5, 6 parameters it is really hard to modify this string.

Anybody knows best method how to create URL string (I mean when we modify it).

Answer 1

This is a sample of how to add parameters in a safe way. Long but reliable.

NSString* const kBaseURL = @"http://maps.google.com/maps/api/geocode/xml";
NSMutableDictionary *parameterDic = [NSMutableDictionary dictionary];
[parameterDic setObject:@"plaza de la puerta del sol 1, madrid, spain" forKey:@"address"];
[parameterDic setObject:@"false" forKey:@"sensor"];

NSMutableArray *parameters = [NSMutableArray array];
for (__strong NSString *name in parameterDic) {
    NSString *value = [parameterDic objectForKey:name];
    name = encodeToPercentEscapeString(name);
    value = encodeToPercentEscapeString(value);
    NSString *queryComponent = [NSString stringWithFormat:@"%@=%@", name, value];
    [parameters addObject:queryComponent];
}
NSString *query = [parameters componentsJoinedByString:@"&"];
NSString *urlString = [NSString stringWithFormat:@"%@?%@", kBaseURL, query];
NSURL *url = [NSURL URLWithString:urlString];
NSLog(@"%@",url);

The code above calls this C function because stringByAddingPercentEscapesUsingEncoding won't convert some special characters in the name or value of the parameters. As pointed by Jesse Rusak see Proper URL (Percent) Encoding in iOS for a discussion.

// remove CFBridgingRelease and __bridge if your code is not ARC
NSString* encodeToPercentEscapeString(NSString *string) {
    return (NSString *)
        CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(NULL,
                                            (__bridge CFStringRef) string,
                                            NULL,
                                            (CFStringRef) @"!*'();:@&=+$,/?%#[]",
                                            kCFStringEncodingUTF8));
}

This prints

http://maps.google.com/maps/api/geocode/xml?sensor=false&address=plaza%20de%20la%20puerta%20del%20sol%201,%20madrid,%20spain

Bonus track: how to deconstruct and rebuild a string:

NSString *stringUrl = @"http://www.google.com:80/a/b/c;params?m=n&o=p#fragment";
NSURL *url = [NSURL URLWithString:stringUrl];
NSLog(@"%@",stringUrl);
NSLog(@"         scheme: %@",[url scheme]);
NSLog(@"           host: %@",[url host]);
NSLog(@"           port: %@",[url port]);
NSLog(@"           path: %@",[url path]);
NSLog(@"   relativePath: %@",[url relativePath]);
NSLog(@"parameterString: %@",[url parameterString]);
NSLog(@"          query: %@",[url query]);
NSLog(@"       fragment: %@",[url fragment]);

NSMutableString *s = [NSMutableString string];
[s appendFormat:@"%@://%@",[url scheme],[url host]];
if ([url port]!=nil){
    [s appendFormat:@":%@",[url port]];
}
[s appendFormat:@"%@",[url path]];
if ([url parameterString]!=nil){
    [s appendFormat:@";%@",[url parameterString]];
}
if ([url query]!=nil){
    [s appendFormat:@"?%@",[url query]];
}
if ([url fragment]!=nil){
    [s appendFormat:@"#%@",[url fragment]];
}
NSLog(@"%@",s);

This prints

http://www.google.com:80/a/b/c;params?m=n&o=p#fragment
         scheme: http
           host: www.google.com
           port: 80
           path: /a/b/c
   relativePath: /a/b/c
parameterString: params
          query: m=n&o=p
       fragment: fragment