C#
Activator.CreateInstance
Learn dynamic instantiation with Activator.CreateInstance.
Activator.CreateInstance
Activator.CreateInstance(typeof(T)) instantiates a type at runtime. It returns object; the caller must provide type safety. DI containers, serializers and plugin systems create instances this way.
For parameterized constructors use Activator.CreateInstance(typeof(T), arg1, arg2); the matching constructor is called. When the type is only known at runtime (e.g. from a config file), Activator replaces new.
Parameterized constructors
The call Activator.CreateInstance(typeof(T), 5, "text") finds the constructor whose signature matches and invokes it. The argument count, order and types must match; otherwise a MissingMethodException is thrown.
The result returns as object?; cast to the real type with as or a cast. DI containers use this to resolve dependencies; e.g. Activator.CreateInstance(typeof(MyService), logger).
Exercise Create an instance dynamically and print the type name
Create an instance dynamically with object obj = Activator.CreateInstance(typeof(Sample));. Print obj.GetType().Name with Console.WriteLine.
Show example solution
Create the instance with object obj = Activator.CreateInstance(typeof(Sample));. Print the type name with Console.WriteLine(obj.GetType().Name);.
Example solution:
using System;
class Sample
{
public string Name { get; set; } = "Test";
}
class Program
{
static void Main()
{
object obj = Activator.CreateInstance(typeof(Sample));
Console.WriteLine(obj.GetType().Name);
}
}
Test yourself
-
Match the method to its purpose
- Activator.CreateInstance
- Creates an instance
- typeof(T)
- Gives a Type object
- GetType()
- Runtime type
- GetMethods()
- Method list
-
Complete the CreateInstance call
object obj = Activator.____(typeof(Sample));
Show answer
object obj = Activator.CreateInstance(typeof(Sample));
-
What does Activator.CreateInstance return?
- An object instance
- A Type object
- A MethodInfo
- null
Show answer
An object instance — Correct. Activator.CreateInstance returns an object instance.
Next lesson: MethodInfo.Invoke
