如果var为null，如何忽略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.

Answer 1

I would really refactor it this way:

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

Answer 2

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 : "";
}

Answer 3

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

Answer 4

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));
    }

Answer 5

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.