Why reflection is needed in C Sharp (C#) - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why use reflection in C#?

Reflection lets a program look at its own parts while running. Why might this be useful?

A To find out the names and types of properties in an object at runtime

B To permanently change the source code of a program

C To speed up the program by avoiding method calls

D To make the program run without any errors

💡 Hint

Think about when you want to learn about an object without knowing its details before running the program.

Reflection allows a program to inspect objects, types, and members during execution. This helps when you don't know the exact types or properties beforehand.

❓ Predict Output

intermediate

Output of reflection code

What will this C# code print?

C Sharp (C#)

using System;
using System.Reflection;

class Person {
    public string Name { get; set; } = "Alice";
    public int Age { get; set; } = 30;
}

class Program {
    static void Main() {
        Person p = new Person();
        Type t = p.GetType();
        foreach (PropertyInfo prop in t.GetProperties()) {
            Console.WriteLine($"{prop.Name}: {prop.GetValue(p)}");
        }
    }
}

A

Name: Alice
Age: 30

B Compilation error

C

Name: Alice
Age: 0

D

Name: 
Age: 0

💡 Hint

Look at how reflection gets property names and values from the object.

The code uses reflection to get all properties of the Person object and prints their names and current values. Since Name is "Alice" and Age is 30, it prints those.

🔧 Debug

advanced

Why does this reflection code throw an exception?

What error does this code cause and why?

C Sharp (C#)

using System;
using System.Reflection;

class Program {
    static void Main() {
        Type t = Type.GetType("NonExistentClass");
        Console.WriteLine(t.Name);
    }
}

A No error, prints 'NonExistentClass'

B TypeLoadException because the class does not exist

C Compilation error because NonExistentClass is undefined

D NullReferenceException because Type.GetType returned null

💡 Hint

What happens if Type.GetType cannot find the class?

Type.GetType returns null if the class is not found. Then accessing t.Name causes a NullReferenceException.

📝 Syntax

advanced

Correct way to get method info using reflection

Which option correctly gets the MethodInfo for a method named 'Calculate' in class 'MathOps'?

C Sharp (C#)

class MathOps {
    public int Calculate(int x) { return x * 2; }
}

A MathOps.GetMethod(Calculate)

B MathOps.GetMethod("Calculate")

C typeof(MathOps).GetMethod("Calculate")

D typeof(MathOps).GetMethod(Calculate)

💡 Hint

Remember to use typeof and pass the method name as a string.

typeof(MathOps) gets the Type object. GetMethod requires the method name as a string. Options A and B are invalid because MathOps is used directly and is not a Type object. Option C misses quotes around method name. D is correct.

🚀 Application

expert

Using reflection to invoke a method dynamically

Given this code, what is the output?

C Sharp (C#)

using System;
using System.Reflection;

class Greeter {
    public void SayHello(string name) {
        Console.WriteLine($"Hello, {name}!");
    }
}

class Program {
    static void Main() {
        Greeter g = new Greeter();
        MethodInfo mi = typeof(Greeter).GetMethod("SayHello");
        mi.Invoke(g, new object[] { "Bob" });
    }
}

A Hello, name!

B Hello, Bob!

C Runtime error: TargetParameterCountException

D Compilation error

💡 Hint

Check how Invoke passes parameters as an object array.

The code uses reflection to find the method SayHello and calls it on the Greeter object with parameter "Bob". It prints 'Hello, Bob!'.