解析url中各个参数的值

NSURL* url = [NSURL urlWithString:@"http://www.xxx.com?param1=123¶m2=456"];

解析出param1和parm2的值。

方法如下：

- (NSDictionary*)dictionaryFromQuery:(NSString*)query usingEncoding:(NSStringEncoding)encoding {
    NSCharacterSet* delimiterSet = [NSCharacterSet characterSetWithCharactersInString:@"&;"];
    NSMutableDictionary* pairs = [NSMutableDictionary dictionary];
    NSScanner* scanner = [[[NSScanner alloc] initWithString:query] autorelease];
    while (![scanner isAtEnd]) {
        NSString* pairString = nil;
        [scanner scanUpToCharactersFromSet:delimiterSet intoString:&pairString];
        [scanner scanCharactersFromSet:delimiterSet intoString:NULL];
        NSArray* kvPair = [pairString componentsSeparatedByString:@"="];
        if (kvPair.count == 2) {
            NSString* key = [[kvPair objectAtIndex:0]
                             stringByReplacingPercentEscapesUsingEncoding:encoding];
            NSString* value = [[kvPair objectAtIndex:1]
                               stringByReplacingPercentEscapesUsingEncoding:encoding];
            [pairs setObject:value forKey:key];
        }
    }

    return [NSDictionary dictionaryWithDictionary:pairs];
}