从变量实例化泛型类型

Question

I would like to instantiate a new object where the type and generic type are defined as variables. The final result could look like the newListOfObjects created manually here:

var newListOfObjects = new List<TabViewModel>();

Where TabViewModel is the following object:

public class TabViewModel
{
    public string Title { get; set; }
    public int TabOrder { get; set; }
}

The problem comes when trying to instantiate the new object using only variables . We have one generic type variable, genericType, which is an interface and one list of type arguments, listOfTypeArgs. In the example above the generic type would be IList and the arguments would be TabViewModel. It would then look like following ( note, some code is psudo for easier understanding ):

Type genericType = IList'1;
Type[] listOfTypeArgs = TabViewModel;
var newObject = Activator.CreateInstance(genericType.MakeGenericType(listOfTypeArgs));

It is then obvious that I get the error 'System.MissingMethodException' with the note that I can not instantiate a variable from an interface.

How can I convert the interface to its represenative so that I can instantiate the new object?

NOTE: I can not change Type genericType = IList'1; nor Type[] listOfTypeArgs = TabViewModel;

Answer 1

You need to use the List<> type like so:

var genericType = typeof(List<>);
var boundType = genericType.MakeGenericType(typeof(TabViewModel));
var instance = Activator.CreateInstance(boundType);

Answer 2

The error is self descriptive, you need concrete types to create an instance. Instead of IList (Which has no implementation and is just a contract), you need to use an implementation of IList :

Type genericType = typeof(List<>);
Type[] listOfTypeArgs = new[] { typeof(TabViewModel) };
var newObject = Activator.CreateInstance(genericType.MakeGenericType(listOfTypeArgs));

Edit:

If you don't have a concrete type, you need to get it either using a container or reflecting the current assemblies. Below is a bit of a hack that you need to tweak the way you find useful for your case.

Type genericType = typeof(List<>);
Type concreteType = AppDomain.CurrentDomain.GetAssemblies()
                            .SelectMany(s => s.GetTypes())
                            .Where(p => genericType.IsAssignableFrom(p)).FirstOrDefault();

Type[] listOfTypeArgs = new[] { typeof(TabViewModel) };
var newObject = Activator.CreateInstance(concreteType.MakeGenericType(listOfTypeArgs));