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