Top 20 WPF Interview Questions and Answers (With Detailed Explanations)

 

1. What is WPF?

Answer:
WPF (Windows Presentation Foundation) is a UI framework from Microsoft used for building desktop applications for Windows. It is part of the .NET ecosystem and uses XAML (Extensible Application Markup Language) to create rich user interfaces.

Key Features

• Vector-based rendering

• Hardware acceleration

• Data binding

• Styles & templates

• Animation support

• MVVM architecture compatibility

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2. What is XAML in WPF?

Answer:
XAML stands for Extensible Application Markup Language. It is a declarative language used to design UI elements in WPF.

Advantages

• Clear separation of UI and code-behind

• Easy to maintain

• Designer-friendly

• Reduces code in .cs files

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3. What is MVVM in WPF?

Answer:
MVVM (Model–View–ViewModel) is the most widely used architecture in WPF.

Components

• Model: Business logic & data

• View: XAML (UI)

• ViewModel: Connects view and model using bindings

Benefits

• Testability

• Separation of concerns

• Maintainability

• Reusability of components

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4. What is Data Binding in WPF?

Answer:
Data Binding connects UI elements to data sources such as objects, properties, and collections.

Binding Modes

• OneWay

• TwoWay

• OneTime

• OneWayToSource

Real-time Example

Binding a TextBox to a ViewModel property for editing user input.

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5. What are Dependency Properties?

Answer:
A dependency property is a special type of property used by WPF to enable:

• Data binding

• Styles

• Animation

• Resources

Why Needed?

Normal CLR properties cannot support WPF’s advanced features.

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6. What are Attached Properties?

Answer:
Attached properties are dependency properties used by parent containers to apply behavior to child elements.

**Example:

Grid.Row, Grid.Column**

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7. What is a Routed Event in WPF?

Answer:
Routed events travel through the visual tree.

Types

• Bubbling (child → parent)

• Tunneling (parent → child)

• Direct (control only)

Example

Button Click → bubbles up to Window.

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8. What are Templates in WPF?

Answer:
Templates define how controls look.

Types

• ControlTemplate: Changes visual structure

• DataTemplate: Defines UI for data

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9. What is the Difference Between StaticResource and DynamicResource?

StaticResource	DynamicResource
Loaded at compile time	Loaded at runtime
Faster performance	Can update UI dynamically
Cannot change	Can change

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10. What are WPF Layout Panels?

Answer:
Panels arrange UI elements.

Common Layouts

• Grid

• StackPanel

• WrapPanel

• DockPanel

• Canvas

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11. What is ObservableCollection?

Answer:
A collection that notifies UI automatically when items are added, removed, or updated.

Used commonly in MVVM.

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12. What is ICommand in WPF?

Answer:
ICommand allows binding buttons and UI actions to ViewModel methods.

Benefits

• Removes code-behind

• Improves MVVM structure

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13. What is the Visual Tree in WPF?

Answer:
Visual Tree represents all visual elements of UI including controls and their internal templates.

Used for:

• Rendering

• Event routing

• Template customization

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14. What is Logical Tree in WPF?

Answer:
Logical tree contains high-level UI elements.

Example

Window → Grid → Button

Logical tree is simpler than the visual tree.

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15. What are WPF Styles?

Answer:
Styles group common property values that can be applied to multiple controls.

Benefits

• Reusability

• Consistency

• Easy maintenance

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16. What is Value Converter (IValueConverter)?

Answer:
Converters help transform binding data.

Example

Convert boolean to visibility:

• true → Visible

• false → Collapsed

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17. What is the Dispatcher in WPF?

Answer:
The Dispatcher manages the UI thread. WPF UI elements can be accessed only from the UI thread.

Usage

Dispatcher.Invoke(() => { ... });

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18. What is the Difference Between WPF and WinForms?

WPF	WinForms
Uses XAML	Uses drag & drop designers
Hardware accelerated	GDI+ based
Supports MVVM	No built-in MVVM support
Better animations, graphics	Limited UI capabilities

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19. What is Prism in WPF?

Answer:
Prism is a framework used for enterprise-level WPF applications.

Features

• Dependency Injection

• Navigation

• Event Aggregator

• Modular application support

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20. How to Improve WPF Application Performance?

Key Tips

• Use Virtualization

• Freeze Freezable objects

• Avoid complex layouts

• Reduce data binding overhead

• Enable async operations

• Use BitmapCache for static UI

⭐ Top 50 .NET Interview Questions and Answers (Fully Explained) (Perfect for Freshers + Experienced .NET Developers)-2025

 1. What is .NET Framework?

Answer:
.NET Framework is a Microsoft software development platform used to build Windows, Web, and Enterprise applications. It includes:

• CLR (Common Language Runtime)

• BCL (Base Class Library)

• Languages: C#, VB.NET, F#

• Tools: Visual Studio

It allows cross-language interoperability and simplifies memory management via the CLR.

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2. What is .NET Core / .NET 5+?

Answer:
.NET Core (now unified under .NET 5, .NET 6, .NET 7, .NET 8) is:

• Cross-platform (Windows, Linux, macOS)

• Open-source

• High-performance and lightweight

• Supports microservices, containers, and cloud-native apps

It replaced the old .NET Framework with a unified modern platform.

---

3. What is the CLR?

Answer:
CLR (Common Language Runtime) is the runtime environment of .NET.
It handles:

• Memory management

• Garbage Collection

• Thread management

• Exception handling

• Code execution

• Security

It converts MSIL (Microsoft Intermediate Language) into native machine code.

---

4. What is the difference between .NET Framework and .NET Core?

Answer:

Feature	.NET Framework	.NET Core/.NET 6+
Platform	Windows-only	Cross-platform
Open Source	Limited	Fully open-source
Performance	Moderate	High-performance
Deployment	System-level	Side-by-side
Architecture	Monolithic	Modular

.NET Core is recommended for modern applications, cloud applications, and microservices.

---

5. What is C#?

Answer:
C# (C Sharp) is an object-oriented programming language developed by Microsoft.
Features:

• Strongly typed

• OOP-based

• Garbage-collected

• Supports LINQ, async/await, generics

• Used for web, desktop, API, game development (Unity), cloud apps.

---

6. What is MSIL/IL Code?

Answer:
MSIL (or IL) is the intermediate code generated after compiling C# code.
CLR converts IL to native code using JIT (Just-In-Time) compiler.

---

7. What is JIT Compiler?

Answer:
JIT Compiler converts MSIL into machine code during program execution.
Types of JIT:

• Pre-JIT

• Econo-JIT

• Normal JIT

This improves performance and optimizes based on runtime.

---

8. What is OOPS in C#?

Answer:
OOPS stands for:

• Encapsulation

• Abstraction

• Inheritance

• Polymorphism

It helps create modular, maintainable, and reusable code.

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9. Explain Encapsulation with example.

Answer:
Encapsulation hides internal object details and exposes only required functionality.

Example:

public class BankAccount 
{
    private decimal balance;

    public void Deposit(decimal amount) => balance += amount;

    public decimal GetBalance() => balance;
}

Here, balance is protected from direct access.

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10. What is Inheritance in C#?

Answer:
Inheritance allows one class to inherit properties and methods of another.

Example:

class Car { public void Drive() {} }
class BMW : Car { }

BMW inherits Drive().

---

11. What is Polymorphism?

Answer:
Polymorphism allows methods to behave differently based on runtime objects.

Example:

public virtual void Message() { }
public override void Message() { }

---

12. Difference between Abstract Class and Interface.

Answer:

Abstract Class	Interface
Can have fields	No fields
Can have constructors	No constructors
Supports abstract + concrete methods	Only abstract methods
Single inheritance only	Multiple inheritance

---

13. What are Value Types and Reference Types?

Answer:

• Value types: stored in stack → int, double, struct

• Reference types: stored in heap → class, array, string

---

14. What is Boxing and Unboxing?

Answer:
Boxing: Converting value type → object (heap)
Unboxing: Converting object → value type

Example:

int x = 10;
object obj = x; // Boxing
int y = (int)obj; // Unboxing

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15. What is ASP.NET Core?

Answer:
A high-performance, cross-platform framework for building:

• Web apps

• REST APIs

• Microservices

• Cloud applications

Uses Middleware and Dependency Injection by default.

---

16. What are Middleware components?

Answer:
Middleware is a pipeline that handles HTTP requests in sequence.
Examples:

• Authentication

• Routing

• Exception handling

• Logging

Implemented like:

app.UseMiddleware<CustomMiddleware>();

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17. What is Dependency Injection (DI)?

Answer:
A design pattern where dependencies are injected instead of being created inside classes.

Example:

services.AddScoped<IEmployeeService, EmployeeService>();

Benefits:

• Testability

• Loose coupling

• Readability

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18. What is Entity Framework Core?

Answer:
EF Core is an ORM (Object Relational Mapper) for .NET used to interact with databases using C# instead of SQL.

Features:

• Migrations

• LINQ queries

• Change tracking

• Database-first & Code-first support

---

19. What is Code-First approach?

You create C# classes → EF creates database tables automatically.

---

20. What is Database-First approach?

Database already exists → EF generates models and DbContext.

---

21. What is Migration in EF Core?

Answer:
Migrations track database schema changes.

Commands:

Add-Migration Init
Update-Database

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22. What is LINQ?

Answer:
Language Integrated Query to perform queries on objects, collections, datasets, and DB.

Example:

var data = list.Where(x => x.Age > 20);

---

23. What is async and await?

Answer:
Used for asynchronous programming to avoid thread blocking.

Example:

await Task.Delay(1000);

---

24. What is Garbage Collection in .NET?

Answer:
Automatic memory management that frees unused objects.

Generations:

• Gen 0

• Gen 1

• Gen 2

---

25. What is IDisposable Interface?

Used to release unmanaged resources manually.

Example:

using(var conn = new SqlConnection()) { }

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26. What is a Constructor and Destructor?

Constructor → initializes object
Destructor → frees resources (rare in .NET)

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27. What is Singleton Pattern?

Ensures only one instance of a class exists.

Example:

public static readonly Singleton Instance = new Singleton();

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28. What is Routing in ASP.NET Core?

Matches incoming HTTP requests to endpoints.

Example:

app.MapControllerRoute("default", "{controller}/{action}/{id?}");

---

29. What is Model Binding?

ASP.NET Core automatically maps request data to parameters or models.

---

30. What is ViewModel?

A DTO used between View and Controller to avoid exposing domain models.

---

31. What is REST API?

Architectural style for building stateless, resource-based web services.

---

32. Difference between GET and POST.

GET → Fetch data (idempotent)
POST → Create data (not idempotent)

---

33. What is JWT Token?

A secure token used for authentication between client and server.
Parts:

• Header

• Payload

• Signature

---

34. What is Swagger?

API documentation and testing tool built on OpenAPI specification.

---

35. What is Microservices Architecture?

Application broken into independent services.
Benefits: scalability, fault isolation, cloud readiness.

---

36. What is Kestrel?

The built-in high-performance web server in ASP.NET Core.

---

37. What is Configuration in ASP.NET Core?

Manages app settings using:

• appsettings.json

• Environment variables

• Azure Key Vault

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38. What is CORS?

Cross-Origin Resource Sharing → Allows frontend apps to access APIs from other domains.

---

39. What is a NuGet Package?

Dependency manager for .NET libraries.

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40. What is .NET Standard?

A versioned set of APIs available across all .NET platforms.

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41. Explain Sealed Class.

Cannot be inherited, used for security/performance.

---

42. What is a Partial Class?

A class split into multiple files.

---

43. What is Reflection?

Inspecting metadata during runtime.

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44. What is ADO.NET?

Low-level data access using:

• SqlConnection

• SqlCommand

• SqlDataReader

---

45. What is Thread and Task in .NET?

Thread → independent execution path
Task → lightweight wrapper for async operations

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46. Explain SOLID Principles.

5 design principles for maintainable code:

• Single Responsibility

• Open Closed

• Liskov Substitution

• Interface Segregation

• Dependency Inversion

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47. What is Attribute in C#?

Metadata added to classes or methods.

Example:

[Authorize]
public class HomeController { }

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48. What is Filter in ASP.NET Core?

Executes logic before or after controller actions.
Types:

• Authorization

• Resource

• Action

• Exception

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49. What is Web API Versioning?

Manage multiple versions of APIs for backward compatibility.

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50. What is Health Check in ASP.NET Core?

Used to monitor the health of application and services in production.

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