How to ignore if var is null c#

Question

I'm joining a load of strings to make a superstring but i need to ignore a param if one is null. Currently i cannot think how to do this other than emcompassing all the params in seperate if statements. Help pls:

Here the code

 public void LinkBuilder(string baselink, string sharedkey, string service, string period, string bulletintype,
        string includeresults, string includemap, string username, string password)
    {
        sharedkey = "&" + sharedkey;
        service = "&" + service;
        period = "&" + period;
        bulletintype = "&" + bulletintype;
        includeresults = "&" + includeresults;
        includemap = "&" + includemap;
        username= "&" + username;
        password = "&" + password;

        string completeLink = sharedkey + service + period + bulletintype + includeresults + includemap + username +
                              password;

Not sure how to tackle this.

forgot to include baselink in completeLink. Doesn't really matter, but i thought I'd point it out before someone else does. — marwaha.ks, Sep 17 '15 at 13:26
Aside from anything else, are you sure you don't need to URL-encode the parameters? And do you *really* want to put a password in a URL? — Jon Skeet, Sep 17 '15 at 13:28
Are you talking about `public void Sample(string key, string service = null)`? — Greg, Sep 17 '15 at 13:30
@JonSkeet - its just for internal testing use. It will not be publically available. — marwaha.ks, Sep 17 '15 at 13:32
@Greg - Lets say is sharedkey was null, I do not want it to be overridden with the "&" + sharedkey; or not to be included in the complete link, however since i am overriding sharedkey it will never be null when it gets to "string completeLink", — marwaha.ks, Sep 17 '15 at 13:35
@Kam It sure looks like you're trying to create a url. Are you trying to assemble a query string? If so, you're going about things the wrong way... — spender, Sep 17 '15 at 13:41
@Seth Kitchen, and if I combine Superstrings, will I get a Hyperstring? — Bgl86, Sep 17 '15 at 13:42
I think if you combine two or more epic strings, a kitten will die, or a black hole will be created, who knows. — Bgl86, Sep 17 '15 at 13:44
No, if you combine two epicstrings, you would get a .... sorry, this is GiliusMaximus' wife. He will not be able to continue his post. His brain just exploded. — , Sep 17 '15 at 13:52

Maksim Simkin · Accepted Answer · 2015-09-17T13:39:09.520

21

I would really refactor it this way:

public void LinkBuilder(params string[] links)
{
    string completeLink = String.Join("&", links.Where(x=>!String.IsNullOrEmpty(x)));
}

edited Sep 17 '15 at 13:39

answered Sep 17 '15 at 13:34

Maksim Simkin

9,561
4
36
49

4

Possibly make it a `params` parameter, so the caller doesn't even need to create the array... – Jon Skeet Sep 17 '15 at 13:37
1

for easy use you could add the params keyword public void LinkBuilder(params string[] links) (http://stackoverflow.com/questions/7580277/why-use-the-params-keyword) – fuchs777 Sep 17 '15 at 13:38
ok , i think this is the winner, but I would add the params keyword to the method arguments - public void LinkBuilder(params string[] links) - so that the user can still call it with a number of strings separated by commas - LinkBuilder(mybaselink, mysharedkey, myservice...) - but the method accepts them as a string array. – Sep 17 '15 at 13:40
Also the question didn't request that empty strings should be ignored – Stumblor Sep 17 '15 at 13:40
@Stumblor - but it seems like that would be assumed unless otherwise stated, if null is ignored, empties also. – Sep 17 '15 at 13:45
You also might want to add an "&" at the beginning of the string, since String.join will only put the separator between the strings, and the OP seemed to want one from the beginning. – Sep 17 '15 at 13:46
@GiliusMaximus would this ensure the strings are in order? – marwaha.ks Sep 17 '15 at 13:50
Also sorry to be such a noob, how would i call the LinkBuilder method? LinkBuilder(string baselink, string sharedkey, string service) and it will automatically put the passed param in the array? – marwaha.ks Sep 17 '15 at 13:52
the same as you did it before – Maksim Simkin Sep 17 '15 at 13:53
@Kam - yes, the "where" LINQ operation preserves order. See http://stackoverflow.com/a/204777/4843530 – Sep 17 '15 at 13:57
It worked - this was my output. "http: //xx.aspx?&x&x&x&x&x&x&x&x" which is exactly what I wanted. Thanks guys – marwaha.ks Sep 17 '15 at 14:07
@Kam Seems like a problem, I mean you have `?&x` you have a giant key with no value, and you the `?&` doesn't seem value. – Greg Sep 17 '15 at 14:15
@Greg Nope it works, I have replaced the values. the base link is "...blah.aspx?" – marwaha.ks Sep 17 '15 at 15:46

dremerDT · Answer 2 · 2015-09-17T13:42:03.033

You can do a check of strings by operator ?: in method.

public void LinkBuilder(string baselink, string sharedkey, string service, string period, string bulletintype,
        string includeresults, string includemap, string username, string password)
    {
        sharedkey = checkValue(sharedkey);
        service = checkValue(service );
        period = checkValue(period );
        bulletintype = checkValue(bulletintype );
        includeresults = checkValue(includeresults );
        includemap = checkValue(includemap );
        username= checkValue(username );
        password = checkValue(password );

        string completeLink = sharedkey + service + period + bulletintype + includeresults + includemap + username +
                              password;
}
private String checkValue(String str)
{
    return str != null ? "&" + str : "";
}

use string.IsNullOrEmpty before doing the assignment instead i.e: sharedKey = string.IsNullOrEmpty(sharedKey) ? string.Empty :"&" + sharedKey — Ahmed ilyas, Sep 17 '15 at 13:34

spender · Answer 3 · 2015-09-17T13:57:34.430

Make an enumerable collection of your strings, use a bit of linq to filter out the nulls, then join it all back together again with String.Join:

var elements = 
    new[]{baselink, sharedkey, service, period, 
          bulletintype, includeresults, includemap, 
          username, password};
var nonNullElements = elements.Where(e => e != null);
var outputString = String.Join("&", nonNullElements);

On the off-chance that you're actually trying to assemble a querystring, there are better ways.

For instance, you could leverage HttpUtility and reflection using the following method for parsing an anonymous object to a query string:

public static class ObjEx
{
    public static string ToQueryString(this object data)
    {
        var collection = data.GetType()
            .GetProperties()
            .Aggregate(
                HttpUtility.ParseQueryString(string.Empty),
                (prev,curr) => {
                    var val = curr.GetValue(data);
                    var propName = curr.Name;
                    prev.Add(propName,val.ToString());
                    return prev;
            });
        return collection.ToString();
    }
}

then

var data = new{foo = "bar", num = 1, cat = "bad", dog = "good", needsEscaping = "é\"&"};
Console.WriteLine(data.ToQueryString());

will give you:

foo=bar&num=1&cat=bad&dog=good&needsEscaping=%u00e9%22%26

score 1 · Answer 4 · answered Sep 17 '15 at 13:38

If the objective is to avoid wrapping each parameter in an if statement, you could add them to a list, then use String.Join, and Linq.Select

        public void LinkBuilder(string baselink, string sharedkey, string service, string period, string bulletintype,
            string includeresults, string includemap, string username, string password)
    {
        var allParams = new List<string>
        {
            baselink,
            sharedkey,
            service,
            period,
            bulletintype,
            includeresults,
            includemap,
            username,
            password
        };

        var completeLink = "?" + String.Join("&", allParams.Select(p => p != null));
    }

Greg · Answer 5 · 2015-09-17T13:52:51.363

Below would accept a Collection which I feel may be better maintainable. I re factored a bit.

public string LinkBuilder(Dictionary<string, string> parameters)
{
     var url = String.Empty;
     foreach(var parameter in parameters)
         if(!string.IsNullOrEmpty(parameter.Value))
               url += String.Format("&{0}={1}", parameter.Key, parameter.Value);

     return url;
}

This way you would pass a collection to build your URL, then it would return the giant URL for you. You have a massive selection, I personally like Maksim's answer.

How to ignore if var is null c#

5 Answers5