Creating instances dynamically in C Sharp (C#) - Visual Walkthrough

Concept Flow - Creating instances dynamically

Start

↓

Get Type info

↓

Call Activator.CreateInstance

↓

New object created

↓

Use the object

↓

End

This flow shows how a program gets type information, creates an instance dynamically, and then uses the new object.

Execution Sample

C Sharp (C#)

using System;

class Person {
  public string Name;
  public Person() { Name = "Unknown"; }
}

class Program {
  static void Main() {
    var type = typeof(Person);
    var obj = Activator.CreateInstance(type);
    Console.WriteLine(((Person)obj).Name);
  }
}

This code creates a Person object dynamically and prints its Name property.

Execution Table

Step	Action	Evaluation	Result
1	Get type info	typeof(Person)	Person type info stored in 'type'
2	Create instance	Activator.CreateInstance(type)	New Person object created, stored in 'obj'
3	Access property	((Person)obj).Name	"Unknown"
4	Print output	Console.WriteLine	Outputs: Unknown
5	End	No more code	Program ends

💡 All steps completed, instance created and used successfully.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
type	null	Person type info	Person type info	Person type info	Person type info
obj	null	null	Person instance	Person instance	Person instance
Name	N/A	N/A	N/A	"Unknown"	"Unknown"

Key Moments - 2 Insights

Why do we need to cast 'obj' to Person before accessing 'Name'?

Because Activator.CreateInstance returns an object of type 'object', we must cast it to 'Person' to access Person-specific members like 'Name'. See execution_table step 3.

What happens if the type does not have a parameterless constructor?

Activator.CreateInstance will throw an exception because it requires a parameterless constructor to create the instance. This is implied in step 2 where creation succeeds.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'Name' after step 3?

A null

B "Unknown"

C "Person"

D Throws error

💡 Hint

Check the 'Result' column in step 3 of execution_table.

At which step is the new Person object created?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Action' and 'Result' columns in execution_table for object creation.

If we forget to cast 'obj' to Person, what happens when accessing 'Name'?

A It prints "Unknown" anyway

B Runtime error

C Compilation error

D It prints null

💡 Hint

Casting is needed to access Person members; see key_moments explanation.

Concept Snapshot

Creating instances dynamically in C#:
- Use typeof(TypeName) to get type info.
- Use Activator.CreateInstance(type) to create an object.
- Cast the object to the correct type to access members.
- Requires a parameterless constructor.
- Useful for flexible, runtime object creation.

Full Transcript

This example shows how to create an instance of a class dynamically in C#. First, we get the type information using typeof. Then, we call Activator.CreateInstance with that type to create a new object. Since the method returns a generic object, we cast it to the specific class to access its properties. Finally, we print the Name property which is set to "Unknown" by the constructor. This process allows creating objects when the type is not known until runtime.