Multiple parameters in a List. How to create without a class?

This is probably a pretty obvious question, but how would I go about creating a List that has multiple parameters without creating a class.

Examp开发者_Python百科le:

var list = new List<string, int>();

list.Add("hello", 1);

I normally would use a class like so:

public class MyClass
{
    public String myString {get; set;}
    public Int32 myInt32 {get; set;}
}

then create my list by doing:

var list = new List<MyClass>();
list.Add(new MyClass { myString = "hello", myInt32 = 1 });

If you are using .NET 4.0 you can use a Tuple.

List<Tuple<T1, T2>> list;

For older versions of .NET you have to create a custom class (unless you are lucky enough to be able to find a class that fits your needs in the base class library).

If you do not mind the items being imutable you can use the Tuple class added to .net 4

var list = new List<Tuple<string,int>>();
list.Add(new Tuple<string,int>("hello", 1));

list[0].Item1 //Hello
list[0].Item2 //1

However if you are adding two items every time and one of them is unique id you can use a Dictionary

If appropriate, you might use a Dictionary which is also a generic collection:

Dictionary<string, int> d = new Dictionary<string, int>();
d.Add("string", 1);

Another solution create generic list of anonymous type.

 var list = new[]
 { 
    new { Number = 10, Name = "Smith" },
    new { Number = 10, Name = "John" } 
 }.ToList();

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

This also gives you intellisense support, I think in some situations its better than Tuple and Dictionary.

List only accepts one type parameter. The closest you'll get with List is:

 var list = new List<Tuple<string, int>>();
 list.Add(Tuple.Create("hello", 1));

To add to what other suggested I like the following construct to avoid the annoyance of adding members to keyvaluepair collections.

public class KeyValuePairList<Tkey,TValue> : List<KeyValuePair<Tkey,TValue>>{
    public void Add(Tkey key, TValue value){
        base.Add(new KeyValuePair<Tkey, TValue>(key, value));
    }
}

What this means is that the constructor can be initialized with better syntax::

var myList = new KeyValuePairList<int,string>{{1,"one"},{2,"two"},{3,"three"}};

I personally like the above code over the more verbose examples Unfortunately C# does not really support tuple types natively so this little hack works wonders.

If you find yourself really needing more than 2, I suggest creating abstractions against the tuple type.(although Tuple is a class not a struct like KeyValuePair this is an interesting distinction).

Curiously enough, the initializer list syntax is available on any IEnumerable and it allows you to use any Add method, even those not actually enumerable by your object. It's pretty handy to allow things like adding an object[] member as a params object[] member.

As said by Scott Chamberlain(and several others), Tuples work best if you don't mind having immutable(ie read-only) objects.

If, like suggested by David, you want to reference the int by the string value, for example, you should use a dictionary

Dictionary<string, int> d = new Dictionary<string, int>();
d.Add("string", 1);
Console.WriteLine(d["string"]);//prints 1

If, however, you want to store your elements mutably in a list, and don't want to use a dictionary-style referencing system, then your best bet(ie only real solution right now) would be to use KeyValuePair, which is essentially std::pair for C#:

var kvp=new KeyValuePair<int, string>(2, "a");
//kvp.Key=2 and a.Value="a";
kvp.Key = 3;//both key and
kvp.Value = "b";//value are mutable

Of course, this is stackable, so if you need a larger tuple(like if you needed 4 elements) you just stack it. Granted this gets ugly really fast:

     var quad=new KeyValuePair<KeyValuePair<int,string>, KeyValuePair<int,string>>
                (new KeyValuePair<int,string>(3,"a"),
                new KeyValuePair<int,string>(4,"b"));
//quad.Key.Key=3

So obviously if you were to do this, you should probably also define an auxiliary function.

My advice is that if your tuple contains more than 2 elements, define your own class. You could use a typedef-esque using statement like :

using quad = KeyValuePair<KeyValuePair<int,string>, KeyValuePair<int,string>>;

but that doesn't make your instantiations any easier. You'd probably spend a lot less time writing template parameters and more time on the non-boilerplate code if you go with a user-defined class when working with tuples of more than 2 elements

For those wanting to use a Class.

Create a Class with all the parameters you want

Create a list with the class as parameter

class MyClass
        {
            public string S1;
            public string S2;
        }

List<MyClass> MyList= new List<MyClass>();

Get Schema Name and Table Name from a database.

        public IList<Tuple<string, string>> ListTables()
        {

            DataTable dt = con.GetSchema("Tables");

            var tables = new List<Tuple<string, string>>();

            foreach (DataRow row in dt.Rows)
            {
            string schemaName = (string)row[1];
            string tableName = (string)row[2];
            //AddToList();
            tables.Add(Tuple.Create(schemaName, tableName));
            Console.WriteLine(schemaName +" " + tableName) ;
            }
            return tables;
        }

The new Tuple syntax makes it easier:

var list = new List<(string, int)>();

list.Add("one", 1);

// list[0].Item1 returns "one"
// list[0].Item2 returns 1

Item1 and Item2 are not pretty variable names. You can provide better names:

var list = new List<(string name, int number)>
{
    ("one", 1),
    ("two", 2),
};

// list[0].name   returns "one"
// list[0].number returns 1

Alternatively the custom names can be provided during deconstruction:

var list = new List<(string, int)>
{
    ("one", 1),
    ("two", 2),
};


foreach(var (name, number) in list)
{
    Console.WriteLine($"name: {name}, number: {number}");
}

This works fine with me

List<string> myList = new List<string>();
myList.Add(string.Format("{0}|{1}","hello","1") ;


label:myList[0].split('|')[0] 
val:  myList[0].split('|')[1]