获取URL的指定参数对应值

+ (NSString *) paramValueOfUrl:(NSString *) url withParam:(NSString *) param{

    NSError *error;
    NSString *regTags=[[NSString alloc] initWithFormat:@"(^|&|\\?)+%@=+([^&]*)(&|$)",param];
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:regTags
                                                                           options:NSRegularExpressionCaseInsensitive
                                                                             error:&error];

    // 执行匹配的过程
    NSArray *matches = [regex matchesInString:url
                                      options:0
                                        range:NSMakeRange(0, [url length])];
    for (NSTextCheckingResult *match in matches) {
        NSString *tagValue = [url substringWithRange:[match rangeAtIndex:2]];  // 分组2所对应的串
        return tagValue;
    }
    return nil;
}