Creating instances dynamically in C Sharp (C#) - Practice Exercises

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of dynamic instance creation with Activator.CreateInstance

What is the output of this C# code that creates an instance dynamically?

C Sharp (C#)

using System;

class Person {
    public string Name { get; set; } = "Unknown";
    public override string ToString() => $"Person: {Name}";
}

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

A System.Object

B Person: Unknown

C NullReferenceException

D Person:

💡 Hint

Activator.CreateInstance creates an object using the default constructor.

The code uses Activator.CreateInstance to create a Person object. The default Name is "Unknown", so ToString returns "Person: Unknown".

❓ Predict Output

intermediate

Output when creating instance with parameterized constructor dynamically

What will this C# code print when creating an instance dynamically with parameters?

C Sharp (C#)

using System;
using System.Reflection;

class Car {
    public string Model { get; }
    public Car(string model) {
        Model = model;
    }
    public override string ToString() => $"Car model: {Model}";
}

class Program {
    static void Main() {
        Type t = typeof(Car);
        object obj = Activator.CreateInstance(t, new object[] { "Tesla" });
        Console.WriteLine(obj.ToString());
    }
}

A System.Object

B Car model:

C MissingMethodException

D Car model: Tesla

💡 Hint

Activator.CreateInstance can pass constructor arguments as an object array.

The code calls the constructor with "Tesla" as argument, so the Model property is set to "Tesla" and printed.

🔧 Debug

advanced

Identify the error when creating instance dynamically without default constructor

What error does this code produce when trying to create an instance dynamically?

C Sharp (C#)

using System;

class Book {
    public string Title { get; }
    public Book(string title) {
        Title = title;
    }
}

class Program {
    static void Main() {
        Type t = typeof(Book);
        var obj = Activator.CreateInstance(t);
        Console.WriteLine(obj);
    }
}

A MissingMethodException

B NullReferenceException

C InvalidCastException

D No error, prints Book object

💡 Hint

Activator.CreateInstance without parameters requires a default constructor.

Book has only a constructor with a string parameter. Activator.CreateInstance(t) tries to call a default constructor which does not exist, causing MissingMethodException.

📝 Syntax

advanced

Which code snippet correctly creates an instance dynamically using reflection?

Choose the code snippet that correctly creates an instance of class Animal dynamically with a default constructor.

A var obj = Activator.CreateInstance(typeof(Animal));

B var obj = typeof(Animal).CreateInstance();

C var obj = Activator.CreateInstance<Animal>();

D var obj = new Activator(typeof(Animal));

💡 Hint

Activator.CreateInstance(Type) is the correct method to create an instance dynamically.

Option A uses Activator.CreateInstance with a Type argument correctly. Option A is invalid syntax. Option A uses a generic overload that requires compile-time type information. Option A is invalid because Type does not have CreateInstance method.

🚀 Application

expert

How many instances are created dynamically in this code?

Given this code, how many objects are created dynamically using Activator.CreateInstance?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Shape {
    public string Name { get; set; }
    public Shape() { Name = "Shape"; }
}

class Program {
    static void Main() {
        List<object> shapes = new List<object>();
        Type shapeType = typeof(Shape);
        for (int i = 0; i < 3; i++) {
            var shape = Activator.CreateInstance(shapeType);
            shapes.Add(shape);
        }
        Console.WriteLine(shapes.Count);
    }
}

A 0

B 1

C 3

D 4

💡 Hint

Activator.CreateInstance is called inside a loop 3 times.

The loop runs 3 times, each time creating a new Shape instance dynamically and adding it to the list. So 3 instances are created.