Creating instance of class from System.Type variable

Question

I'm trying to build up a simple game engine in XNA much inspired by Unity. What I'm currently working on is Components that can be attached to gameobjects. I have classes like "PlayerController" and "Collider" that are components and therefor inherits from the Component class.

I'm trying to create methods than can add a new component depending on a Type argument, for example when trying to require a component:

public void RequireComponent(System.Type type)
{
    //Create the component
    Component comp = new Component();
    //Convert the component to the requested type
    comp = (type)comp; // This obviously doesn't work
    //Add the component to the gameobject
    gameObject.components.Add(comp);
}

For example, the rigidbody component needs the gameobject to have a collider, so it requires the collider component:

public override void Initialize(GameObject owner)
{
    base.Initialize(owner);

    RequireComponent(typeof(Collider));
}

Can this be done or is there a better way?

Possible duplicate of [How to create a new object instance from a Type](https://stackoverflow.com/questions/752/how-to-create-a-new-object-instance-from-a-type) — d219, Nov 20 '19 at 20:22

score 4 · Accepted Answer · answered Jun 18 '17 at 17:00

public void RequireComponent(System.Type type)
{
    var comp = (Component)Activator.CreateInstance(type, new object[]{});

    gameObject.components.Add(comp);
}

However, if you find yourself passing in compile time constants, for example typeof(Collider), you might as well do this:

public void Require<TComponent>() where TComponent : class, new()
{
    gameObject.components.Add(new TComponent());
}

and call it like this:

Require<Collider>();

instead of the first version:

RequireComponent(typeof(Collider));

Thanks, your solution really helped me out. Not only did it solve the current problem, but it gave me ways to solve a ton of my ideas. — Charlie Malmqvist, Jun 18 '17 at 17:45

stelioslogothetis · Answer 2 · 2017-06-18T16:48:32.197

To answer your question, the easiest way to get an object when given a Type object is to use the Activator class:

public void RequireComponent(System.Type type)
{
    var params = ; // Set all the parameters you might need in the constructor here
    var component = (typeof(type))Activator.CreateInstance(typeof(type), params.ToArray());
    gameObject.components.Add(component);
}

However, I'm thinking this might be a XY problem. From what I understand, this is your solution for achieving modularity in your game engine. Are you sure however that this is how you want to do it? My recommendation is for you to take some time and read up on polymorphism and related concepts, and how those can be applied in C#, before deciding on your approach.

Creating instance of class from System.Type variable

2 Answers2