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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the type of the object.

C Sharp (C#)

Type type = obj.[1]();

Drag options to blanks, or click blank then click option'

AGetObjectType

BGetClass

CGetType

DTypeOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using TypeOf which is a keyword, not a method.

Using GetClass which does not exist in C#.

The GetType() method returns the runtime type of the current instance.

2fill in blank

medium

Complete the code to get the name of the class using reflection.

C Sharp (C#)

string className = obj.GetType().[1];

Drag options to blanks, or click blank then click option'

ATypeName

BFullName

CClassName

DName

Attempts:

3 left

💡 Hint

Common Mistakes

Using FullName which returns namespace plus class name.

Using ClassName or TypeName which do not exist.

The Name property of the Type object returns the class name without namespace.

3fill in blank

hard

Fix the error in the code to get all public properties of a class.

C Sharp (C#)

PropertyInfo[] properties = obj.GetType().[1]();

Drag options to blanks, or click blank then click option'

AGetProperties

BGetMembers

CGetFields

DGetAttributes

Attempts:

3 left

💡 Hint

Common Mistakes

Using GetFields which returns fields, not properties.

Using GetMembers which returns all members, not just properties.

GetProperties() returns all public properties of the type, which is needed to inspect properties via reflection.

4fill in blank

hard

Fill both blanks to invoke a method named 'Print' with no parameters using reflection.

C Sharp (C#)

MethodInfo method = obj.GetType().[1]("Print");
method.[2](obj, null);

Drag options to blanks, or click blank then click option'

AGetMethod

BInvoke

CCallMethod

DExecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using CallMethod or Execute which do not exist.

Passing parameters incorrectly to Invoke.

GetMethod("Print") gets the method info, and Invoke(obj, null) calls it on the object with no parameters.

5fill in blank

hard

Fill all three blanks to create an instance of a class named 'Person' using reflection.

C Sharp (C#)

Type type = Type.[1]("Person");
object obj = Activator.[2](type);
string name = (string)type.GetProperty("Name").[3](obj);

Drag options to blanks, or click blank then click option'

AGetType

BCreateInstance

CGetValue

DFindType

Attempts:

3 left

💡 Hint

Common Mistakes

Using FindType which does not exist.

Using wrong method to create instance or get property value.

Type.GetType("Person") gets the type, Activator.CreateInstance(type) creates an object, and GetValue(obj) gets the property value.

Practice

1. Why do programmers use reflection in C#?

easy

A. To manage memory manually

B. To write faster code by avoiding loops

C. To examine and use information about types at runtime

D. To create graphical user interfaces

Solution

1. Step 1: Understand what reflection does

   Reflection allows a program to look at its own structure, like classes and methods, while it is running.

2. Step 2: Identify the purpose of reflection

   It is used to examine and interact with types dynamically, not for speed or UI creation.

3. Final Answer:

   To examine and use information about types at runtime -> Option C

4. Quick Check:

   Reflection = runtime type info [OK]

Hint: Reflection inspects types during program run [OK]

Common Mistakes:

• Confusing reflection with UI design
• Thinking reflection speeds up code
• Believing reflection manages memory

2. Which of the following is the correct way to get the type of an object obj using reflection in C#?

easy

A. Type t = obj.GetType();

B. Type t = GetType(obj);

C. Type t = typeof(obj);

D. Type t = obj.Type();

Solution

1. Step 1: Recall the method to get an object's type

   In C#, the method GetType() is called on the object instance to get its type.

2. Step 2: Check each option's syntax

   Type t = obj.GetType(); uses obj.GetType(), which is correct. Type t = GetType(obj); and D are invalid syntax. Type t = typeof(obj); uses typeof incorrectly because it expects a type name, not an object.

3. Final Answer:

   Type t = obj.GetType(); -> Option A

4. Quick Check:

   obj.GetType() gets type [OK]

Hint: Use obj.GetType() to get runtime type [OK]

Common Mistakes:

• Using typeof with an object instance
• Calling non-existent methods like obj.Type()
• Trying to pass object to GetType as argument

3. What will be the output of this C# code?

using System;
class Program {
  static void Main() {
    var type = typeof(string);
    Console.WriteLine(type.Name);
  }
}

medium

A. string

B. String

C. System.String

D. Type

Solution

1. Step 1: Understand typeof operator

   typeof(string) returns the Type object for the string class.

2. Step 2: Check what type.Name returns

   The Name property returns the class name without namespace, which is "String" with capital S.

3. Final Answer:

   String -> Option B

4. Quick Check:

   typeof(string).Name = "String" [OK]

Hint: typeof(T).Name returns class name without namespace [OK]

Common Mistakes:

• Confusing lowercase 'string' keyword with class name
• Expecting full namespace in Name property
• Thinking output is 'Type'

4. Identify the error in this reflection code snippet:

Type t = typeof(int);
var method = t.GetMethod("Parse");
int result = method.Invoke(null, new object[] { "123" });
Console.WriteLine(result);

medium

A. Invoke returns object, needs casting to int

B. GetMethod("Parse") does not exist on int

C. typeof(int) should be typeof(Int32)

D. Invoke cannot be called with null as first argument

Solution

1. Step 1: Check method retrieval

   int (System.Int32) has a static method "Parse", so GetMethod("Parse") works.

2. Step 2: Check Invoke return type and usage

   Invoke returns an object. Assigning it directly to int causes a compile error. It needs explicit cast: (int)method.Invoke(...).

3. Final Answer:

   Invoke returns object, needs casting to int -> Option A

4. Quick Check:

   Invoke returns object, cast needed [OK]

Hint: Cast Invoke result to correct type [OK]

Common Mistakes:

• Ignoring cast from object to int
• Thinking GetMethod("Parse") is invalid
• Assuming typeof(int) is wrong

5. You want to load a plugin assembly at runtime and call its method Run without knowing the class name beforehand. Which reflection approach is best?

hard

A. Call Run method without loading assembly

B. Use typeof() with class name, then call Run directly

C. Use new operator with class name string

D. Use Assembly.Load, then find type with GetTypes(), then invoke Run method

Solution

1. Step 1: Understand dynamic plugin loading

   When class name is unknown, you must load assembly dynamically and inspect types.

2. Step 2: Use reflection to find and invoke method

   Assembly.Load loads the plugin. GetTypes() lists classes. Then you find the class with Run method and invoke it.

3. Final Answer:

   Use Assembly.Load, then find type with GetTypes(), then invoke Run method -> Option D

4. Quick Check:

   Dynamic loading needs Assembly.Load + reflection [OK]

Hint: Load assembly, find type, invoke method dynamically [OK]

Common Mistakes:

• Using typeof() without knowing class name
• Trying to instantiate class by string name directly
• Calling method without loading assembly