Creating Object Instances Dynamically

In object-oriented programming, it’s often necessary to create instances of classes dynamically. This can be achieved using various methods in .NET. In this tutorial, we will explore different approaches to creating object instances from a given type.

Introduction to Type and Activator Classes

The Type class represents a type declaration, such as a class, interface, or enumeration. The Activator class provides static methods for creating objects and obtaining references to non-public members of a type using reflection.

Creating an Instance Using the Activator Class

One way to create an instance of a type is by using the Activator.CreateInstance method. This method returns an object that represents the instance created.

Type objectType = typeof(MyClass);
object instance = Activator.CreateInstance(objectType);

Alternatively, you can use the generic version of CreateInstance, which allows for a more readable and type-safe way to create instances:

MyClass instance = (MyClass)Activator.CreateInstance(typeof(MyClass));
// or using generics
MyClass instance = Activator.CreateInstance<MyClass>();

Creating an Instance Using Type.GetType

Another approach is to use the Type.GetType method, which returns a Type object that represents the specified type. You can then pass this Type object to the Activator.CreateInstance method.

string typeName = "MyNamespace.MyClass";
Type type = Type.GetType(typeName);
object instance = Activator.CreateInstance(type);

However, if the fully qualified name of the type is in another assembly, Type.GetType will return null. To handle this scenario, you can iterate through all assemblies and find the type:

public object GetInstance(string strFullyQualifiedName)
{
    Type type = Type.GetType(strFullyQualifiedName);
    if (type != null)
        return Activator.CreateInstance(type);
    foreach (var asm in AppDomain.CurrentDomain.GetAssemblies())
    {
        type = asm.GetType(strFullyQualifiedName);
        if (type != null)
            return Activator.CreateInstance(type);
    }
    return null;
}

Creating an Instance Using Compiled Expressions

For better performance, especially when creating instances repeatedly at runtime, you can use compiled expressions. The Expression class provides a way to create and compile expressions.

static readonly Func<MyClass> myClassCreator = Expression.Lambda<Func<MyClass>>(
    Expression.New(typeof(MyClass).GetConstructor(Type.EmptyTypes))
).Compile();

MyClass instance = myClassCreator();

Comparison of Methods

Each method has its own trade-offs in terms of readability, performance, and applicability. The choice of which method to use depends on the specific requirements of your application.

| Method | Readability | Performance |
| — | — | — |
| Activator.CreateInstance | Medium | Medium |
| Type.GetType | Low | Medium |
| Compiled Expressions | High | High |

Best Practices

When creating object instances dynamically, consider the following best practices:

• Use the Activator class when you need to create an instance of a type that is known at runtime.
• Use Type.GetType when you have the fully qualified name of the type as a string.
• Use compiled expressions for better performance in scenarios where instances are created repeatedly.

Conclusion

In conclusion, creating object instances dynamically in .NET can be achieved using various methods. By understanding the trade-offs and best practices associated with each method, you can choose the most suitable approach for your specific use case.