How to use class name as parameter in C#

Solution 1:

Object createObjectBy(Type clazz){
   // .. do construction work here
    Object theObject = Activator.CreateInstance(clazz);
    return theObject;
}

Usage:

createObjectBy(typeof(A));

Or you could simply use Activator.CreateInstance directly :-)

Solution 2:

The ideal way would be to use generics

Type is known at design time

public static T CreateInstance<T>() where T: new()
{
    // Do some business logic
    Logger.LogObjectCreation(typeof(T));

    // Actualy instanciate the object
    return new T();
}

A call example would look like

var employee = CreateInstance<Employee>();

Type is unknown at runtime

If the type of object is unknown at runtime, for example through a plugin system, you need to use the Type class:

public static object CreateInstance(Type type)
{
    // Do some business logic
    Logger.LogObjectCreation(type);

    // Actualy instanciate the object
    return Activator.CreateInstance(type);
}

A call example would look like

var instance = CreateInstance(someType);

Performance

Of course, nothing beats instanciating an object than by using the keyword new. Except maybe not instanciating, but instead reusing an object, like through caching.

If you have to settle for the second method where the type is unknown, there are some alternatives to Activator.CreateInstance. Although the article recommend using lambda expression, your biggest consideration is:

Does your unknown object need to be instantiated often in a short period of time, or do you only create it once

If you only need to create your object once, just stick with the Activator.CreateInstance method. If you need to create it multiple time in a short time, try the lambda approach. That last approach is similar to a compiled regular expression vs. an on-the-fly regular expression.

Solution 3:

C# doesn't support this. But what are you trying to do?

You probably could use:

createObjectBy(Type type);

createObjectBy<T>();

Solution 4:

Use the class Type. You can return an instance of it by call

obj.GetType();

or without an object instance

typeof(className);

I hope it helps.