define a List like List<int,string>?

I need a two column list like:

List<int,string> mylist= new List<int,string>();

it says

> using the generic type System.collection.generic.List<T> requires 1 type arguments.

Depending on your needs, you have a few options here.

If you don't need to do key/value lookups and want to stick with a List<>, you can make use of Tuple<int, string>:

List<Tuple<int, string>> mylist = new List<Tuple<int, string>>();

// add an item
mylist.Add(new Tuple<int, string>(someInt, someString));

If you do want key/value lookups, you could move towards a Dictionary<int, string>:

Dictionary<int, string> mydict = new Dictionary<int, string>();

// add an item
mydict.Add(someInt, someString);

You could use an immutable struct

public struct Data
{
    public Data(int intValue, string strValue)
    {
        IntegerData = intValue;
        StringData = strValue;
    }

    public int IntegerData { get; private set; }
    public string StringData { get; private set; }
}

var list = new List<Data>();

Or a KeyValuePair<int, string>

using Data = System.Collections.Generic.KeyValuePair<int, string>
...
var list = new List<Data>();
list.Add(new Data(12345, "56789"));

With the new ValueTuple from C# 7 (VS 2017 and above), there is a new solution:

List<(int,string)> mylist= new List<(int,string)>();

Which creates a list of ValueTuple type. If you're targeting .NET Framework 4.7+ or .NET/.NET Core, it's native, otherwise you have to get the ValueTuple package from nuget.

It's a struct opposing to Tuple, which is a class. It also has the advantage over the Tuple class that you could create a named tuple, like this:

var mylist = new List<(int myInt, string myString)>();

That way you can access like mylist[0].myInt and mylist[0].myString

Since your example uses a generic List, I assume you don't need an index or unique constraint on your data. A List may contain duplicate values. If you want to insure a unique key, consider using a Dictionary<TKey, TValue>().

var list = new List<Tuple<int,string>>();
       
list.Add(Tuple.Create(1, "Andy"));
list.Add(Tuple.Create(1, "John"));
list.Add(Tuple.Create(3, "Sally"));
    
foreach (var item in list)
{
    Console.WriteLine(item.Item1.ToString());
    Console.WriteLine(item.Item2);
}

Use C# Dictionary datastructure it good for you...

Dictionary<string, int> dict = new Dictionary<string, int>();
dict.Add("one", 1);
dict.Add("two", 2);

You can retrieve data from Ditionary in a simple way..

foreach (KeyValuePair<string, int> pair in dict)
{
    MessageBox.Show(pair.Key.ToString ()+ "  -  "  + pair.Value.ToString () );
}

For more example using C# Dictionary... C# Dictionary

Navi.

Not sure about your specific scenario, but you have three options:

1.) use Dictionary<..,..>
2.) create a wrapper class around your values and then you can use List
3.) use Tuple

List<Tuple<string, DateTime, string>> mylist = new List<Tuple<string, DateTime,string>>();
mylist.Add(new Tuple<string, DateTime, string>(Datei_Info.Dateiname, Datei_Info.Datum, Datei_Info.Größe));
for (int i = 0; i < mylist.Count; i++)
{
     Console.WriteLine(mylist[i]);
}

For that, you could use a Dictionary where the int is the key.

new Dictionary<int, string>();

If you really want to use a list, it could be a List<Tuple<int,string>>() but, Tuple class is readonly, so you have to recreate the instance to modifie it.