轉自http://www.cnblogs.com/PleaseInputEnglish/archive/2013/12/25/3489707.html

修改了一下，代碼如下

- (NSString *)query:(NSString *)key fromUrlStr:(NSString *)urlStr
{
    NSError *error;
    NSString *regTags=[[NSString alloc] initWithFormat:@"(^|&|\\?)+%@=+([^&]*)(&|$)", key];
    NSRegularExpression *regEx = [NSRegularExpression regularExpressionWithPattern:regTags
                                                                           options:NSRegularExpressionCaseInsensitive
                                                                             error:&error];
    
    // 執(zhí)行匹配的過程
    NSArray *matches = [regEx matchesInString:urlStr
                                      options:0
                                        range:NSMakeRange(0, [urlStr length])];
    for (NSTextCheckingResult *match in matches) {
        NSString *tagValue = [urlStr substringWithRange:[match rangeAtIndex:2]];
        return tagValue;
    }
    return @"";
}