Top Windows Phone interview questions c# - Part1

                 Windows Phone Basic Questions

1. LifeCycle Of WindowsPhone:

  App Launching=>Running=> OnNavigatedFrom(NavigationEventArgs)=>deactivated=>dormanent (stopped and no processing takes place)=>tombstoned(app has been terminated and it will be relaunched and the application can use the preserved data to restore state) =>Activated=> OnNavigatedTo(NavigationEventArgs) =>Closing=>raised when the user navigates backwards past the first page of an app

2. ContentTemplate:

Gets or sets the data template used to display the content of the ContentControl

ControlTemplate: Specifies the visual structure and behavioral aspects of a Control that can be shared across multiple instances of the control..

Control: Represents the base class for UI elements that use a ControlTemplate to define their appearance.

3. DataTemplate:

Describes the visual structure of a data object.

4. ItemTemplate:

·         Gets or sets the custom content for the data item in a control.ex:listbox

·         ItemsControl: Represents a control that can be used to present a collection of items.

·         ItemsPresenter: Specifies where items are placed in a control, usually an ItemsControl.

·          ItemPanelTemplate:specify the panel used to arrange the children of your ListBox.

·         ItemSource: Gets or sets a collection used to generate the content of the ItemsControl.

5. Layouts:

Windows Phone provides a flexible layout system that enables you to specify how controls are positioned on the screen.

i)Absolute layout(Canvas): you arrange child elements in a layout panel by specifying their exact locations relative to their parent element

ii)Dynamic Layout(Stack Panel,Grid): To use automatic or proportional sizing, you must assign special values to the Height andWidth properties.

6. StackPanel Vs Grid Vs Canvas Vs WrapPanel:

StackPanel: The StackPanel is a simple layout panel that arranges its child elements into a single line that can be oriented horizontally or vertically. 

Grid: The Grid control is the most flexible layout panel, and supports arranging controls in multi-row and multi-column layouts.

Canvas:  Canvas is useful for scenarios where the UI elements contained within it never move.

WrapPanel or WrapGrid : Positions child elements sequentially from left to right or top to bottom. When elements extend beyond the container edge, elements are positioned in the next row or column. In Windows Phone 8, consider using the WrapPanel available in the Windows Phone Toolkit.

7. What is  Diff B/W Grid column_2  2* and column_4  2*:

Suppose there  4 columns in grid

Column _2  2*: After the Auto columns are calculated, the column gets part of the remaining width. Column 2 will be one-half as wide as Column 4.

Column _4  2*: After the Auto columns are calculated, the column gets part of the remaining width. Column 4 will be two times as wide as Column 2.

8. Panel:

Provides a base class for all Panel elements. Use Panel elements to position and arrange child objects in Windows Phone applications.

9. Style:

A Style is basically a collection of property settings applied to multiple instances of the same type. AStyle contains a collection of one or more Setter objects. Each Setter has a Property and a Value. TheProperty is the name of the property of the element the style is applied to. The Value is the value that is applied to the property.

Implicit Styles: For example, if you create a style implicitly for all the ToggleButton controls in your application, and your application has ToggleButton and CheckBox controls (CheckBox derives from ToggleButton), the style is applied only to the ToggleButton controls.

BasedOn Styles: It is possible to build a new style based on an existing style. You can do this using the BasedOnproperty. This reduces the duplication of code and makes it easier to manage resources. Each style supports only one BasedOn style. 

10. UserControl:

Provides the base class for defining a new control that encapsulates related existing controls and provides its own logic.

11. Pivot vs Panorama:

Panorama control is really meant for rich Hub type look .. smooth multi-screen scrolling with Parallax effect, ideally including images in the views. The Pivot control is more for presenting slices of the related data to the user or categorizing the content .. the in-built emails & calendar are examples. Both controls are very suited for dynamic data-binding.

12. Animation:

You have to make the Storyboard a resource that is available to the object that you want to animate. The

Storyboard: Controls animations with a timeline, and provides object and property targeting information for its child animations.

13. ViewBox:

Defines a content decorator that can stretch and scale a single child to fill the available space.

14. VirtualizingStackPanel:

Arranges and virtualizes content on a single line that is oriented either horizontally or vertically.

Virtualization: With UI virtualization, the complete data set is stored in memory. Sometimes, your data set is so large that it can't or shouldn't be stored in memory all at once. In this case, you can use data virtualization to get only a subset of the data to work with. The ItemsControl can still apply UI virtualization to the subset of data created by data virtualization.

15. ObservableCollection<T>:

Represents a dynamic data collection that provides notifications when items get added, removed, or when the whole list is refreshed which is most important in listbox data binding .

16. INotifyPropertyChanging:

The INotifyPropertyChanging interface allows the app to notify the DataContext when it is modifying a property that will ultimately be submitted as an update to the database. The DataContext can use that notification as a trigger to create the copy. This way, only the items that are actually changing need to be duplicated.

17.How many ways to store data in windows phone:

1.  Application settings(IsolatedStorageSettings)

2.  Files and folders(IsolatedStoarge)

3.  Database(SQL CompatEdition): LINQ to SQL is used to define the database schema, select data, and save changes to the underlying database file residing in isolated storage.

External Storage: WP7 does not support application's access to external storage. By limiting the use of external storage, WP7 provides the application with a safe-sandbox, and prevents unpredictable behavior caused by missing external storage or corruption of data by other applications.

18.Interface vs AbstractClass:

Abstract classes can have implementations for some of its members, but the interface can't have implementation for any of its members.

Interfaces cannot have fields where as an abstract class can have fields.

An interface can inherit from another interface only and cannot inherit from an abstract class, where as an abstract class can inherit from another abstract class or another interface.

A class can inherit from multiple interfaces at the same time, where as a class cannot inherit from multiple classes at the same time.

Abstract class members can have access modifiers where as interface members cannot have access modifiers.

19.MVVM:

The Model-View-ViewModel (MVVM) pattern is an application pattern that isolates the user interface from the underlying business logic. MVVM belongs to a class of patterns called Separated Presentation. These patterns provide a clean separation between the UI and the rest of the application. This improves the testability of the application and allows the application and its UI to evolve more easily and independently.

20.Silverlight:

Silverlight is a powerful development platform for creating engaging, interactive user experiences for Web, desktop, and mobile applications when online or offline. Silverlight is a part of the Visual Studio package.

21.XAML:

Extensible Application Markup Language (XAML) is a declarative language. Specifically, XAML can initialize objects and set properties of objects, using a language structure that shows hierarchical relationships between multiple objects, and using a backing type convention that supports extension of types. You can create visible UI elements in the declarative XAML markup. You can then use a separate code-behind file to respond to events and manipulate the objects you declare in XAML. 

22.Metro:

Windows 8 marks the next step in the evolution of the Metro design style. Through the bold use of color, typography and motion

23.WindowPhone Resolutions:

Resolution	Resolution	Aspect ratio	Delta from Windows Phone OS 7.1	Scaled resolution
WVGA	480 × 800	15:9	None. This is the only supported resolution for Windows Phone OS 7.1.	480 × 800
WXGA	768 × 1280	15:9	1.6x scale	480 × 800
720p	720 × 1280	16:9	1.5x scale, 80 pixels taller (53 pixels, after scaling)	480 × 853
1080p	1080 x 1920	16:9	1.5x scale, 80 pixels taller (53 pixels, after scaling)	480 × 853

24.DataBinding:

Data binding provides a simple way for Windows Phone apps to display and interact with data. The way data is displayed is separated from the management of the data. A connection, or binding, between the UI and a data object allows data to flow between the two. When a binding is established and the data changes, the UI elements that are bound to the data can reflect changes automatically. Similarly, changes made by the user in a UI element can be reflected in the data object. For example, if the user edits the value in a TextBox, the underlying data value is automatically updated to reflect that change.

Some common binding scenarios include binding a ListBox to a list of headlines, an input form's TextBoxto a customer data object, or an Image to the current user's photo.

25.DataContext:

The most important aspect of data context is the data source that is used for binding. The most frequent use of DataContext is to set it directly to a CLR data source object. The CLR data source might be a class if it is a static starting data set. Or you can create a local data source as a newObservableCollection<T>, and then update that collection through WCF Data Services or other techniques..

The data context can also hold other characteristics of the binding other than the data source, such as a path into the data source.

26.FrameworkElement:

Provides a framework of common APIs for objects that participate in Windows Phone layout.FrameworkElement also defines APIs related to data binding, object tree, and object lifetime feature areas in Windows Phone.

27.WindowsPhone .Net Framework:

Windows Phone 8 brings a lot of new features to developers and behind the scenes there are also some major improvements. The .NET framework 4.5 and the new C# compiler come with several major new features.

28.async and wait:

you can call an asynchronous method in a synchronous way by simply prefixing it with await inside async method.

29.WebClient vs HttpWebRequest:

In general, WebClient is good for quick and dirty simple requests and HttpWebRequest is good for when you need more control over the entire request.

Also WebClient doesn't have timeout property. And that's the problem, because default value is 100 seconds and that's too much to indicate if there's no Internet connection.

The main difference between the two is that WebClient is basically a wrapper around HtppWebRequest and exposes a simplified interface. 
Apart from that (at least in WP7, not sure about WP8), WebClient only works on the user thread, which is not a good thing. If you want to wait for the reply on a background thread, you need to use HttpWebRequest.

30.Soap vs xml:

SOAP(Simple Object Access Protocol) is a specialization of XML, as it has a schema, such as http://www.xmlsoap.org/soap/envelope/, whereas XML is more general.

but basically SOAP is done via POST, though Axis2 appears to have support for GET, as a way to have SOAP work in a world where REST seems to rule.

If you use XML over http, it may be better, depending on the need, as a way to transfer data, but in the use cases I can think of it would seem better to just use JSON and REST, but, if you want to transfer XML, or send XML, then you could look at using REST.

31.JSON:

HTTP-based Web services frequently use JavaScript Object Notation (JSON) messages to return data back to the client. JSON objects can easily be instantiated in JavaScript, without parsing logic, which makes it a convenient format for messages in Web applications.

 DataContractJsonSerializer. Serializes objects to the JavaScript Object Notation (JSON) and deserializes JSON data to objects. This class cannot be inherited.

32. MemoryStream:

The MemoryStream Class creates a stream whose backing store is memory. The current position of a stream is the position at which the next read or write operation could take place. The current position can be retrieved or set through the Seek method. When a new instance of MemoryStream is created, the current position is set to zero.

33. BitmapImage:

XAML usage for BitmapImage as an object element is uncommon, because it would only be appropriate for setting a BitmapImage as the object element within a property element usage for setting Image.Source. More typically you would use Image and use the URI to set Image.Source as an attribute.

34. WriteableBitmap:

The WriteableBitmap class has a security model that restricts access to the Pixels array, if theWriteableBitmap is constructed using cross-domain content. For example, a WriteableBitmap that is constructed using a BitmapImage referencing a URL that comes from another domain does not permit access to its Pixels array. The restriction extends to any UI element that uses a URL-derived property for setting some or all of its content.

You can still access PixelHeight and PixelWidth properties of WriteableBitmap even if created from protected content. This information can be useful for determining the natural size of content.

35. PushNotification:

Push notification allows an app to notify you of new messages or events without the need to actually open the application, similar to how a text message will make a sound and pop up on your screen.

i)Toast: Toast notifications are system-wide notifications that do not disrupt the user workflow or require intervention to resolve.  Let’s say you’re using the search application. If you were to receive a toast notification, it would display at the top of the screen for ten seconds before disappearing. If the toast notification is tapped, the application that sent the toast notification will launch. The notification can be dismissed with a simple flick of the finger.

ii)Tile:  Every application has a tile, or image, that is displayed if the user pins the application to the Start screen. This tile can be updated with a push notification.

iii)Raw: f your application is not currently running, the raw notification is discarded on the Microsoft Push Notification Service and is not delivered to the device. The payload of a raw notification has a maximum size of 1 KB.

Note: Finally, each device has a 15 channel limit when it comes to push notifications.

36. xap file:

XAP (pronounced ZAP) is the file extension for a Silverlight-based application package (.xap). This file contains the compressed assemblies and resources of a Silverlight 2 application.

The X doesn't mean anything. I've asked, too.

From what I can tell, they didn't want it to look too much like *.ZIP or *.SAP.

But in generally, XAP is also the extension for XACT Audio Projects, open able with the Microsoft Cross-Platform Audio Creation Tool. Silverlight XAP Files are not open able with the Audio Creation Tool, and XACT XAP files are not archives.

37. dll:

A dynamic-link library (DLL) file is an executable file that allows programs to share code and other resources necessary to perform particular tasks. Microsoft Windows provides DLL files that contain functions and resources that allow Windows-based programs to operate in the Windows environment.

38. XNA:

XNA Game Studio 4.0 is a programming environment that allows you to use Visual Studio to create games for Windows Phone, the Xbox 360 console, and Windows-based computers. XNA Game Studio includes the XNA Framework, which is a set of managed libraries designed for game development based on Microsoft .NET Framework 2.0.

39. Navigate between Pages:

We can navigate between windows phone pages using NavigationService.
E.g.: NavigationService.Navigate(new Uri("/MainPage.xaml", UriKind.Relative));

40. How do make grid as scrollable:

We can make a grid, infact any control, scrollable by wrapping in the ScrollViewer
E.g.: Following code snippet shows the way to wrap grid in ScrollViewer and make it scrollable.

        <StackPanel Grid.Row="1" >

            <ScrollViewer>

                <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0" ScrollViewer.ManipulationMode="System">

                    <TextBlock Height="30" HorizontalAlignment="Left" Margin="12,91,0,0" Name="textBlock1" Text="First Name"/>

                    <TextBlock Height="30" HorizontalAlignment="Left" Margin="13,148,0,0" Name="textBlock2" Text="Last Name"/>

                </Grid>

            </ScrollViewer>

        </StackPanel>

41. What is serialization?:

Serialization is the process of converting an object into a stream of bytes.

De-serialization is the opposite process of creating an object from a stream of bytes. 

Serialization / De-serialization is mostly used to transport objects.

42. What are the advantages of get and set properties in C#?:

The get property accessor is used to return the property value.

The set property accessor is used to assign a new value.

43. What is the difference between an abstract method & virtual method?:

An Abstract method does not provide an implementation and forces overriding to the deriving class (unless the deriving class also an abstract class), where as the virtual method has an implementation and leaves an option to override it in the deriving class. Thus Virtual method has an implementation & provides the derived class with the option of overriding it. Abstract method does not provide an implementation & forces the derived class to override the method.

44. What are sealed classes in c#?:

The sealed modifier is used to prevent derivation from a class.

A compile time error occurs if a sealed class is specified as the base class of another class.

45. What is the syntax to inherit from a class in C#?:

class MyNewClass : MyBaseClass

46. What is static member?

The member defined as static which can be invoked directly from the class level, rather than from its instance.

47. What is event?

An event is an action performed based on another method of the program.

An event is a delegate type dass member that is used by an object or a class to provide a notification to other objects that an event has occurred.

An event can be declared with the help of the event keyword.

48. Define namespace?

6The namespace are known as containers which will be used to organize the hierarchical set of .Net classes.

49. What is the difference between Custom Control and User Control?

Custom Controls are compiled code (Dlls), easier to use, difficult to create, and can be placed in toolbox. Drag and Drop controls. 

Attributes can be set visually at design time. Can be used by Multiple Applications (If Shared Dlls), Even if Private can copy to bin directory of web application add reference and use. Normally designed to provide common functionality independent of consuming Application. 

User Controls are similar to those of ASP include files, easy to create, can not be placed in the toolbox and dragged - dropped from it. A User Control is shared among the single application files.

50. What is Delegates?

Delegates are a type-safe, object-oriented implementation of function pointers and are used in many situations where a component needs to call back to the component that is using it.

51.  What is the use of using statement in C#?

The using statement is used to obtain a resource, execute a statement, and then dispose of that resource.

52.  What is the difference between ref & out parameters?

An argument passed to a ref parameter must first be initialized. Compare this to an out parameter, whose argument does not have to be explicitly initialized before being passed to an out parameter.

53.   What is the use of enumerated data type?

An enumerated data type is another user defined type which provides a way for attaching names to numbers thereby increasing comprehensibility of the code. The enum keyword automatically enumerates a list of words by assigning them values 0,1,2, and so on.

54.   What is the difference between Object and Instance?

An instance of a user-defined type is called an object. We can instantiate many objects from one class.

An object is an instance of a class.

55.  What is boxing and unboxing?

Implicit conversion of value type to reference type of a variable is known as BOXING, for example integer to object type conversion. 

Conversion of reference type variable back to value type is called as UnBoxing.

56.  What is the difference between public, static and void?

public: The keyword public is an access modifier that tells the C# compiler that the Main method is accessible by anyone.

static: The keyword static declares that the Main method is a global one and can be called without creating an instance of the class. The compiler stores the address of the method as the entry point and uses this information to begin execution before any objects are created.

void: The keyword void is a type modifier that states that the Main method does not return any value.

57.Dynamic or Runtime Polymorphism.?

Run time Polymorphism also known as method overriding. In this Mechanism by which a call to an overridden function is resolved at a Run-Time (not at Compile-time) if a base Class contains a method that is overridden. Method overriding means having two or more methods with the same name, same signature but with different implementation. In this process, an overridden method is called through the reference variable of a superclass, the determination of the method to be called is based on the object being referred to by reference variable.

58.VisualState:

A VisualState specifies how the control looks when it is in a certain state. For example, when a Button is pressed, its border might be a different color than normal. TheVisualState class has a Storyboard property that changes the appearance of the control. When the control enters the state that is specified by the VisualState.Name property, the Storyboard begins. When the control exits the state, the Storyboard stops.

59.Collection:

A Collection is simply an object that knows how to manage references to multiple instances of other classes. It keeps track of other objects. There are different collections to choose from. Each of them with their own “powers”. Some are created to keep objects sorted; some are created to allow for easy retrieval. The use of collections is quite common in the .NET Framework Class Library.

Ex: Array, list, dictionary 

60.Thread:

Portions of the program code associated with the process

61.ThreadPool:

The thread pool manages a set of threads and uses a queue to assign work items to threads as they become available. The thread pool is similar to the asynchronous programming patterns available in the Windows Runtime because it can be used to accomplish extended work without blocking the UI

62.Difference between DataContractSerializer and XMLSerializer

 DataContractSerializer:

 A practical benefit of the design of the DataContractSerializer is better performance over Xmlserializer. This is because DataContratSerializer explicitly shows the which fields or properties are serialized into XML. 

·         The DataContractSerializer can translate the HashTable into XML. 

·         DataContractSerializer uses the opts-in approach i.e, selecting the members that needs to be serialized .This is called as opts-in approach. 

·         DataContractSerializer can able to serialize types that implements Idictionary.

·         We can serialize a type that marked with [Serializable] attribute with DataContractSerializer. It serializes all the members (private, public) even they are marked with [XmlIgnore]. 

 XMLSerializer:

    XMLSerializer does not provide better performance when compare with DataContratSerializer because XMLSerializer does not indicate which fields or properties of the type are serialized into XML

·         XMLSerializer cannot translate the HashTable into XML

·         XmlSerializer cannot serialize private members 

·         XmlSerializer uses opts-out approach i.e., marking the members do not need to be serialized. This is called as opts-out approach. 

·         Only the public members are serialized not the private members. Suppose we do not need any of the member to be serialized we can use [XmlIgnore] attribute 

63.WebService:

 It has an interface described in a machine-processable format (specifically WSDL(web services description language). Other systems interact with the Web service in a manner prescribed by its description using SOAP messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards

We can identify two major classes of Web services:

·         REST-compliant Web services, in which the primary purpose of the service is to manipulate XML representations of Web resources using a uniform set of stateless operations.

·         Arbitrary Web services, in which the service may expose an arbitrary set of operations.

64.WSDL vs ASMX WebService:

ASMX(Active Server Methods (Microsoft filename extension)):You use an *.asmx file to create an ASP.NET Web Service.  This file contains your service implementation and is needed for hosting the service.

WSDL(web services description language):ASP.NET automatically generates the WSDL or "service description" for your service by reflecting over the types in your service.  You can see the WSDL for your service by browsing to your ASMX file, which should show you a help page for your service containing a link to the service description for the service.  The WSDL can also generally be reached by appending "?wsdl" to the address of the asmx file.

65.OpenDataProtocol(ODATA) webservices:

It is an entity model used to access data as REST webservice ,which can be used to execute queries and to create, update and delete data on to the remote data service.ODATA service allows to querying data over http protocol and retrieve the result in a plain xml format. 

66.Common Language Runtime(CLR):

The Common Language Runtime (CLR) is the virtual machine component of Microsoft's .NET framework and is responsible for managing the execution of .NET programs. In a process known as just-in-time compilation, the compiled code is converted into machine instructions that, in turn, are executed by the computer's CPU. The CLR provides additional services including memory management, type safety and exception handling. All programs written for the .NET framework, regardless of programming language, are executed by the CLR. It provides exception handling, garbage collection and thread management. CLR is common to all versions of the .NET framework.

66.Tile:

Tiles are nothing but linking the application to home screen with updated status.Here two types of tiles

·         Application Tile: This type is used when application is pinned to start screen by the user can easily accessing application icon from app list. So that click on icon will direly navigated to app.

·         Secondary Tile: This type of tiles are created programmatically by user interaction. This type of tiles are used to navigate to application And are created only once. We need to use Create(Uri,ShellData) method to create secondary tile.

66. Application Bar :

The default Application Bar is a row of icon buttons and an ellipsis along the bottom of the phone’s screen. The user can click the ellipsis to display the labels for the icon buttons and menu items if they are enabled. The Application Bar has built-in animation that is displayed as the menu is shown or hidden. Also, the Application Bar automatically adjusts when the phone changes orientation. When the phone is in landscape orientation, the Application Bar appears on the side of the screen vertically. This maximizes the remaining space for page content.

66. Menu :

 The Menu control presents a list of items that specify commands or options for an application. Typically, clicking an item on a menu opens a submenu or causes an application to carry out a command. Menu is an ItemsControl, which means it can contain a collection of objects of any type (such as string, image, or panel).

67. Portable Class :

Portable Class Libraries have been available since .NET Framework 4. You can use them to create portable assemblies that can target multiple platforms, including Windows 7, Windows 8, Windows Phone, Silverlight, and Xbox 360

Note:In this post,i am posted  interview question about windows phone and c#.net. Because it is good practice for knowing generic questions about c#.net which is related to windows phone development.However in next post i am  introducing the most of questions related to windows phone in Part-2

Have a nice day by Subramanyam Raju