获取 string里面的第一个url

+ (NSString *)getFirstUrlFromString:(NSString *)searchText {
    
    NSRange range = [searchText rangeOfString:@"((http[s]{0,1}|ftp)://[a-zA-Z0-9\\.\\-]+\\.([a-zA-Z]{2,4})(:\\d+)?(/[a-zA-Z0-9\\.\\-~!@#$%^&*+?:_/=<>]*)?)|(www.[a-zA-Z0-9\\.\\-]+\\.([a-zA-Z]{2,4})(:\\d+)?(/[a-zA-Z0-9\\.\\-~!@#$%^&*+?:_/=<>]*)?)" options:NSRegularExpressionSearch];
    if (range.location != NSNotFound) {
        NSString *url = [searchText substringWithRange:range];
        if (!([[url hasPrefix:@"http://"] || [url hasPrefix:@"https://"])) {
            url = [@"http://" stringByAppendingString:url];
        }
        
        return url;
    }
    
    return nil;
}