c# how to add a reference for a struct to an array or list?

Question

New to c# and object oriented I am creating predefined data held in structs (that will not change). and I want to add a reference to those structs in either an array or a list The thought process is to then loop through an array of these structs and if the filter criteria is met, to then add an element of the struct "Displayname" to a listbox Example I am using here is for an array

    public struct ListboxData
    {
        public string Category;
        public string Displayname;
        public string ID;
        public List<string> IDTags;
        public string FaultTxt;
        public string Suggestion;
        public string Comments;
        public List<string> MoreQuestions;
    }

    public ListboxData COOLING = new ListboxData
    {
        Category = "CATEGORY",
        Displayname = "COOLING",
        ID = "CAT_COOL",
        IDTags = { ""},
        FaultTxt = "",
        Suggestion = "",
        Comments = "",
        MoreQuestions = { ""}
    };

Having now created multiple instances of the ListboxData structs I then want to add a selection of some of these structs to an array. In this case the Struct reference COOLING

Example of what I am trying to achieve

public ListboxData[] ARRAYofCATEGORIES =
{
    COOLING
};

How can I achieve this ?

Answer 1

I re-wrote your example, working. You can find a live test here

Below is the code. I used a List() since you mentioned in your question that it was acceptable, and I am more used to it.

I don't know what you were doing wrong since you didn't show us a full example. You can read the code bellow, tell me if there is something you don't understand/want and i'll update my answer to fit your needs :-)

Here is the code

public struct ListboxData { private readonly string _category;

    private readonly string _displayname;
    private readonly string _id;
    private readonly List<string> _idTags;
    private readonly string _faultTxt;
    private readonly string _suggestion;
    private readonly string _comments;
    private readonly List<string> _moreQuestions;

    public ListboxData(string category, string displayname, string id, List<string> idTags, string faultTxt, string suggestion, string comments, List<string> moreQuestions)
    {
        _category = category;
        _displayname = displayname;
        _id = id;
        _idTags = idTags;
        _faultTxt = faultTxt;
        _suggestion = suggestion;
        _comments = comments;
        _moreQuestions = moreQuestions;
    }

    public string Category
    {
        get { return _category; }
    }

    public string Displayname
    {
        get { return _displayname; }
    }


    public string Id
    {
        get { return _id; }
    }


    public List<string> IdTags
    {
        get { return _idTags; }
    }


    public string FaultTxt
    {
        get { return _faultTxt; }
    }


    public string Suggestion
    {
        get { return _suggestion; }
    }


    public string Comments
    {
        get { return _comments; }
    }


    public List<string> MoreQuestions
    {
        get { return _moreQuestions; }
    }
}

public class Test
{
    public List<ListboxData> Categories = new List<ListboxData>();
    public CoolingListTest()
    {            
        Categories.Add(new ListboxData(
            category: "CATEGORY",
            displayname: "COOLING",
            id: "CAT_COOL",
            idTags: new List<String> { "" },
            faultTxt: "",
            suggestion: "",
            comments: "",
            moreQuestions: new List<String> { "" }
         ));
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        var test = new Test(); 

        Console.WriteLine(test.Categories.First().Displayname);
    }
}

Answer 2

1st rule to go by is that you have to design immutability into struct. Especially if the fields are reference types (string, array, user classes).

I will demonstrate below a simplified example of populating a struct with various values, then creating a collection (array or list) of the struct and then finally slicing one of the values as an array.

See live code here this code:

public struct ListboxData
{        
    public ListboxData(
        int id,
        string category,
        string name,
        params string[] tags) : this()
    {
        this.ID = id;
        this.Category = category;
        this.Name = name;
        this.Tags = new List<string>();
        this.Tags.AddRange(tags);
    }      
    public int ID { get; private set; }
    public string Category { get;  private set;}
    public string Name { get;  private set;}
    public List<string> Tags { get;  private set;}

    public string[] ToStringArray() 
    {
        return new[] {
            ID.ToString(),
            Category,
            Name,
            string.Join(";", Tags)
        };
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        //Your code goes here
        Console.WriteLine("Hello, world!");

        var list = new List<ListboxData>();
        list.Add(new ListboxData(1001, "COOLING", "Cooling Intro"));
        list.Add(new ListboxData(1002, "COOLING", "Cooling Adanced"));
        list.Add(new ListboxData(1003, "COOLING", "Cooling Tests"));
        list.Add(new ListboxData(1004, "HEATING", "Heating Intro", "tag1", "tag2"));

        // Get all cooling ID's
        int[] ids = list.Where((item)=> item.Category=="COOLING").Select( (item)=> item.ID).ToArray();
        // { 1001, 1002, 1003 }

        foreach(var item in ids)
        {
            Console.WriteLine(item);
        }

        // Get all items that contain "Intro" in the name
        ListboxData[] intro = list.Where((item)=>item.Name.Contains("Intro")).ToArray();
        // { list[0], list[3] }
        foreach(var item in intro)
        {
            Console.WriteLine(item.Name);
        }
    }
}

_{Newer versions of c# have simplifications for the above code. You can omit the private set; statements in the properties.}