Create IEnumerable<T> and add items to it

Question

I have a given type and a Comma Separated Values string :

Type type = service.getType();

String csv = "1,2,3";

I need to convert the csv string to an IEnumerable of type .

I know that type will be numeric, eg, int , short , long , etc.

I am able to spit the csv and convert each one to given type ..

String[] inputs = csv.Split(',');

TypeConverter converter = TypeDescriptor.GetConverter(modelType);

if (converter != null) {

  foreach (String input in inputs) {
    if (converter.CanConvertTo(type)) {
      var number = converter.ConvertFromString(input);
      // Add number to an IEnumerable of numbers
    }

  }

}

I am not able to create an IEnumerable of type and add numbers to it.

How can I do this?

Answer 1

You actually have the type at run-time, so you will need to use reflection to create an object of type List<T> where T is the instance of class Type which you are getting from service. The following code will create an instance of type List<T> while T is not type at compile time but instead it is resolved at run-time. Following is the code to create that:

var listTypeInstance = typeof(List<>);
var instanceList = listTypeInstance.MakeGenericType(type);

var numbers = (IList)Activator.CreateInstance(instanceList);

Now you can call the Add method and add each number in it like:

var number = converter.ConvertFromString(input);
numbers.Add(number);

Adjusted in your code will look something like following:

var listTypeInstance = typeof(List<>);
var instanceList = listTypeInstance.MakeGenericType(type);

var numbers = (IList)Activator.CreateInstance(instanceList);

foreach (String input in inputs) {
    if (converter.CanConvertTo(type)) {
      var number = converter.ConvertFromString(input);
      // Add number to an IEnumerable of numbers
      numbers.Add(number);
    }

Answer 2

Use dynamic to skip the compile-time error.

var runtimeTypes = new List<Type>
{
    typeof(int),
    typeof(long)
};
foreach (var item in runtimeTypes)
{
    var listType = typeof(List<>).MakeGenericType(item);
    dynamic list = Activator.CreateInstance(listType);
    list.Add(1); // Call Add() on dynamic works!
    Console.WriteLine(list[0]);
}