Top 46 WPF Interview Questions And Answers

Question 1

What is WPF?

Accepted Answer

**WPF** stands for Windows Presentation Foundation. It's a re-invention of a UI for Desktop applications using WPF. Apart from dropping controls on "**Windows Forms**" just as developers have been doing for years, WPF provides an extra rapid boost to the application development including Rich User Interface, Animation and much more.

In a nutshell the following things can be done using WPF:

*   Draw normal controls and graphics.
*   Can easily load/play audio and video files.
*   Can provide smooth graphical effects such as drop shadows and color gradients.
*   Can use shared styles which can be used across the same controls to provide the same theme, skin and design.
*   Transforming objects including shapes, controls and video.
*   Can create and animate 3D graphics.
*   Can easily draw vector graphics that scale without jagged aliasing.

**Advantages**

*   Tight multimedia integration
*   Resolution independence
*   Hardware acceleration

Question 2

What is XAML in WPF and why do we need it?

Accepted Answer

XAML is a XML file which represents your WPF UI. The whole point of creating the UI representation in XML was write once and run it anywhere. So the same XAML UI can be rendered as windows application with WPF and the same UI can be displayed on the browser using WPF browser or Silverlight application.

Question 3

What is Command Design Pattern in WPF?

Accepted Answer

Command Design Pattern is one of the most powerful design patterns in object oriented design patterns. This pattern allows you to decouple the request of an action from the object that actually performs an action, in other words a command pattern represents an action as an object. A Command object does not contain the functionality that is to be executed. This removes the direct link between the command definitions and the functionality and it’s promoting a loose coupling. When you want to implement operations based on the user request then the command pattern is the best pattern to handle your object.

The following are the members of the Command Design Pattern:

*   Client
*   Invoker
*   Command
*   Concrete Command
*   Receiver

Question 4

What are Resources in WPF?

Accepted Answer

Windows Presentation Foundation (WPF) resources provide a simple way to reuse commonly defined objects and values. Resources in WPF allow you to set the properties of multiple controls at a time. For example, you can set the background property on several elements in a WPF application using a single resource.

The best way of defining the resources is on a Window or Page element level. Any resource that you define for an element also applies to their child elements of that element.

Question 5

What are differences between Visibility.Collapsed and Visibility.Hidden in WPF?

Accepted Answer

* `Visibility.Hidden` hides the control, but reserves the space it occupies in the layout. So it renders whitespace instead of the control.
* `Visibilty.Collapsed` does not render the control *and* does not reserve the whitespace. The space the control would take is 'collapsed', hence the name.

Question 6

What are static and dynamic resources?

Accepted Answer

There are two types of resource, namely,

*   Static Resource - The value of StaticResource is determined at the time of loading.
*   Dynamic Resource - Dynamic Resource we use in a situation where we want to change the value of property at run time.

Question 7

What is value convertor in WPF?

Accepted Answer

A **Value Converter** functions as a bridge between a target and a source and it is necessary when a target is bound with one source, for instance you have a text box and a button control. You want to enable or disable the button control when the text of the text box is filled or null.

In this case you need to convert the string data to Boolean. This is possible using a Value Converter. To implement Value Converters, there is the requirement to inherit from **I Value Converter** in the **System.Windows.Data** namespace and implement the two methods **Convert** and **Convert Back.**

Question 8

What is the difference between XML and XAML?

Accepted Answer

Following are the differences between XML and XAML:

1. All XAML docs are also authentic XML documents. However, the reverse cannot be true.
2. XAML is a declarative application language while XML is a markup language.
3. XML is primarily used in web applications. In contrast, the XAML is used to design controls of Windows and other web applications.
4. XAML focuses on object properties, definition and the relationship among them.
5. XML is a markup language produced by W3C and is used to describe other markup languages.

Question 9

What is the difference between xmlns and xmlns:x in WPF?

Accepted Answer

Both the namespaces helps to define/resolved XAML UI elements.
* The first namespace is the default namespace and helps to resolve overall WPF elements.
* The second namespace is prefixed by “x:” and helps to resolve XAML language definition.

For instance for the below XAML snippet , we have two things one is the “StackPanel” and the other is “x:name”. “StackPanel” is resolved by the default namespace and the “x:name” is resolved by using “xmlns:x” namespace.

```xml
<StackPanel x:Name="myStack" />
```

Question 10

What are the different kinds of controls in WPF?

Accepted Answer

WPF controls can be categorized into four categories:

*   **Control: -** This is the basic control with which you will work most of time. For example textbox, buttons etc. Now controls which are standalone control like a button , text box , labels etc are termed as content control. Now there are other controls which can hold other controls, for instance itemscontrols. Itemscontrol can have multiple textbox controls, label controls etc.
*   **Shape: -** These controls help us to create simple graphic controls like Ellipse, line, rectangle etc.
*   **Panel: -** These controls help to align and position the controls. For instance, grid helps us to align in a table manner, stack panel helps for horizontal and vertical alignment.
*   **Content presenter: -** This control helps to place any XAML content inside it. Used when we want to add dynamic controls on a WPF screen.

Top 46 WPF Interview Questions

What is XAML in WPF and why do we need it?

What is WPF?

When should we use “x:name” vs “name” ?

What are Resources in WPF?

What are differences between Visibility.Collapsed and Visibility.Hidden in WPF?

What is the difference between xmlns and xmlns:x in WPF?

What is the difference between XML and XAML?

What is value convertor in WPF?

What are the different kinds of controls in WPF?

What is the need of WPF when we had windows forms?

What are static and dynamic resources?

What is Command Design Pattern in WPF?

Explain WPF styles

Is XAML meant only for WPF ?

What is xmlns in XAML file?

What is MVVM?

Name some advantages of using Windows Forms instead of WPF

What is Freezable Object?

Can you explain the overall architecture of WPF?

What is the difference between Visual and Logical Tree in WPF?

What is the difference between style and resource in WPF?

Does that mean WPF has replaced DirectX?

What is Command Design Pattern and ICommand in WPF?

In WPF, what are the differences between the x:Name and Name attributes?

What's the difference between StaticResource and DynamicResource in WPF?

How can you explain view and view model in MVVM?

Does WPF build on top of Windows Forms or are they totally different?

How to globally catch exceptions in a WPF application?

ListBox vs. ListView - what and when to choose for data binding?

Could you tell me what is the main differences between Style and ControlTemplate?

What is the use of a Dispatcher Object in WPF?

What is the difference between a Page and a Window in WPF when you are adding a new file in the Solution Explorer?

Can you explain the complete WPF object hierarchy?

Name some advantages of using WPF instead of Windows forms

What is the relationship between Threads and Dispatchers?

What is the difference between ObservableCollection and BindingList?

What's the difference between ContentControl and ContentPresenter?

What is difference between a ControlTemplate and a DataTemplate in WPF?

Why do we need dependency properties?

What is the difference between Freezable.Clone() & Freezable.CloneCurrentValue() methods?

What is the exact difference between Bubbling Events and Tunneling events?

Explain the difference between SelectedItem, SelectedValue and SelectedValuePath?

In what scenarios does freezing WPF objects benefit performance greatly?

What is the difference between Property and Dependency Property?

What framework for MVVM should I use?

When should I use dependency properties in WPF?