Activator.CreateInstance in C# – A Quick Rundown

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Activator.CreateInstance in C# is one of the main tools we have when it comes to reflection in C#. This article is a quick look at how we can leverage Activator.CreateInstance as a brief primer on using reflection within C#.

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What Is Activator.CreateInstance?

Now, let’s explore Activator.CreateInstance and understand how it enables dynamic object creation. The Activator class is a part of the System namespace in C# and provides methods for creating instances of types. The CreateInstance method specifically allows us to create an instance of a type without having to declare it explicitly in code.

How To Use Activator.CreateInstance?

To use Activator.CreateInstance, we first need to specify the type we want to create an instance of. We can pass either the type name or a Type object representing the type we want to instantiate. Additionally, if the type requires constructor arguments, we can pass them as parameters to CreateInstance.

Let’s consider a simple example where we have a class named Person with properties like Name and Age. We can dynamically create an instance of this class using Activator.CreateInstance as follows:

Type personType = typeof(Person);
object personInstance = Activator.CreateInstance(personType);

In the above code snippet, we obtain the Type object for the Person class using the typeof operator. Then, we pass this type to Activator.CreateInstance, which returns an object instance of the Person class.

Handling Constructor Arguments with Activator.CreateInstance

Often, classes require constructor arguments for their instantiation. We can handle this scenario by passing the required arguments to Activator.CreateInstance. Let’s extend our previous example to include a parameterized constructor in the Person class:

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }

    public Person(string name, int age)
    {
        Name = name;
        Age = age;
    }
}

Now, when creating an instance of Person using Activator.CreateInstance, we need to supply the necessary constructor arguments:

Type personType = typeof(Person);
object personInstance = Activator.CreateInstance(
    personType,
    "John Doe",
    30);

In this case, we provide the arguments "John Doe" and 30 to CreateInstance, which will be used by the constructor of the Person class to initialize the properties.

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Quick Recap on Activator.CreateInstance in C

Activator.CreateInstance is a helpful tool that we have access to when it comes to reflection in C#. We looked at a quick set of simple code examples that show us how to create objects and pass parameters in the constructors.

Reflection in C# is a powerful tool — but it’s easy to abuse. Activator.CreateInstance opens up new possibilities for creating flexible and extensible code, allowing for dynamic object creation and manipulation. By leveraging reflection properly (i.e. without overdoing it at every possible opportunity) in your projects, you can build some really cool things. It allows you to create objects on the fly, based on runtime information, and opens up opportunities for more dynamic systems — like leveraging plugins!

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Comments

[deexter]

Have you tried some benchmark? Where do you think is proper usecase for activator?

[Dev Leader]

I personally don't use reflection for things on a hot path of an application - just for plugin initialization mostly. As a result, I have not benchmarked this kind of code vs calling a constructor directly, but certainly through reflection I would expect a slowdown.

I'm not sure how bad it gets though, but it's never been in a situation where I've needed to worry :) For example, if you were using this kind of approach in a game and needed to use Activator.Instance to create objects, I'd suspect you'd want to look for another way (or run benchmarks to see truly how good/bad it is).

But yeah, "proper" case for me is really when you have no other choice when it comes to dynamically creating objects that you don't know type information about at compile time. Plugins are an excellent example :)

[deexter]

I have tried some simple benchmark and here are some results

public class FakeClass
{
    public FakeClass(string Value, int Number)
    {
        this.Value = Value;
        this.Number = Number;
    }

    public string Value { get; set; }

    public int Number { get; set; }
}

[MemoryDiagnoser]
public class Bench
{
    [Benchmark]
    public void CreateInstance()
    {
        Activator.CreateInstance(typeof(FakeClass), "Test", 10);
    }

    [Benchmark]
    public void New()
    {
        new FakeClass( "Test", 10);
    }
}

| Method         | Mean       | Error     | StdDev    | Gen0   | Allocated |
|--------------- |-----------:|----------:|----------:|-------:|----------:|
| CreateInstance | 215.839 ns | 3.5229 ns | 2.9418 ns | 0.0267 |     336 B |
| New            |   3.156 ns | 0.0823 ns | 0.0687 ns | 0.0025 |      32 B |

[Dev Leader]

I ended up creating a YouTube video to dive a bit deeper into this :)

youtu.be/Djq7eMI_L-4

Let me know if you find that helpful!