State Management in ASP.NET

State management is the process by which you maintain state and page information over multiple requests for the same or different pages.

Types of State Management

There are 2 types State Management:

1. Client Side State Management

This stores information on the client's computer by embedding the information into a Web page, a uniform resource locator(url), or a cookie. The techniques available to store the state information at the client end are listed down below:

View State

Asp.Net uses View State to track the values in the Controls. You can add custom values to the view state. It is used by the Asp.net page framework to automatically save the values of the page and of each control just prior to rendering to the page. When the page is posted, one of the first tasks performed by page processing is to restore view state.

Sample Code

//To Save Information in View State

ViewState.Add("Cherukuri", "Venkateswarlu");

//Retrieving View state

Label1.Text = (string)ViewState["Cherukuri"];

Control State

If you create a custom control that requires view state to work properly, you should use control state to ensure other developers don’t break your control by disabling view state.

Hidden fields

Like view state, hidden fields store data in an HTML form without displaying it in the user's browser. The data is available only when the form is processed.

Sample Code

//Declaring a hidden variable

HtmlInputHidden hidCherukuri = null;

//Populating hidden variable

hidCherukuri.Value = "Venkateswarlu";

//Retrieving value stored in hidden field.

Label1.Text = hidCherukuri.Value;

New Features in ASP.NET 4 and Visual Studio 2010 Web Development

Core Services  Webconfig File Refactoring Extensible Output Caching Auto-Start Web Applications Permanently Redirecting a Page Shrinking Session State Expanding the Range of Allowable URLs Extensible Request Validation Object Caching and Object Caching Extensibility Extensible HTML, URL, and HTTP Header Encoding Performance Monitoring for Individual Applications in a Single Worker Process Multi-Targeting Ajax jQuery Included with Web Forms and MVC Content Delivery Network Support ScriptManager Explicit Scripts Web Forms Setting Meta Tags with the PageMetaKeywords and PageMetaDescription Properties Enabling View State for Individual Controls Changes to Browser Capabilities Routing in ASPNET 4 Setting Client IDs Persisting Row Selection in Data Controls ASPNET Chart Control FiltFiltering Data with the QueryExtender Control Html Encoded Code Expressions Project Template Changes CSS Improvements Hiding div Elements Around Hidden Fields Rendering an Outer Table for Templated Controls ListView Control Enhancements CheckBoxList and RadioButtonList Control Enhancements CheckBoxList and RadioButtonList Control Enhancements Menu Control Improvements Wizard and CreateUserWizard Controls ASPNET MVC Annotation Attribute Validation Support Templated Helpers Dynamic Data Enabling Dynamic Data for Existing Projects Declarative DynamicDataManager Control Syntax Entity Templates New Field Templates for URLs and E-mail Addresses Creating Links with the DynamicHyperLink Control Support for Inheritance in the Data Model Support for Many-to-Many Relationships (Entity Framework Only) New Attributes to Control Display and Support Enumerations Enhanced Support for Filters Visual Studio 2010 Web Development Improvements Improved CSS Compatibility HTML and JavaScript Snippets JavaScript IntelliSense Enhancements Web Application Deployment with Visual Studio 2010 Web Packaging Webconfig Transformation Database Deployment One-Click Publish for Web Applications

ASP.NET Page Life Cycle Overview

 ASP.NET Page Life Cycle Overview

ASP.NET Page Life Cycle Overview

When an ASP.NET page runs, the page goes through a life cycle in which it performs a series of processing steps. These include initialization, instantiating controls, restoring and maintaining state, running event handler code, and rendering. It is important for you to understand the page life cycle so that you can write code at the appropriate life-cycle stage for the effect you intend. Common Life-cycle Events Page Event Typical Use PreInit Raised after the start stage is complete and before the initialization stage begins. Use this event for the following: · Check the IsPostBack property to determine   whether this is the first time the page is being   processed.   . The IsCallback and IsCrossPagePostBack properties   have also been set at this time. · Create or re-create dynamic controls. · Set a master page dynamically. · Set the Theme property dynamically. · Read or set profile property values. Init Raised after all controls have been initialized and any skin settings have been applied. The Init event of individual controls occurs before the Init event of the page. Use this event to read or initialize control properties. InitComplete Raised at the end of the page's initialization stage. Only one operation takes place between the Init andInitComplete events: tracking of view state changes is turned on. View state tracking enables controls to persist any values that are programmatically added to the ViewState collection. Until view state tracking is turned on, any values added to view state are lost across postbacks. Controls typically turn on view state tracking immediately after they raise their Init event. Use this event to make changes to view state that you want to make sure are persisted after the next postback. PreLoad Raised after the page loads view state for itself and all controls, and after it processes postback data that is included with the Request instance. Load The Page object calls the OnLoad method on the Page object, and then recursively does the same for each child control until the page and all controls are loaded. The Load event of individual controls occurs after the Load event of the page. Use the OnLoad event method to set properties in controls and to establish database connections. Control events Use these events to handle specific control events, such as a Button control's Click event or a TextBoxcontrol's TextChanged event. LoadComplete Raised at the end of the event-handling stage. Use this event for tasks that require that all other controls on the page be loaded. PreRender Raised after the Page object has created all controls that are required in order to render the page, including child controls of composite controls. (To do this, the Page object calls EnsureChildControls for each control and for the page.) The Page object raises the PreRender event on the Page object, and then recursively does the same for each child control. The PreRender event of individual controls occurs after the PreRender event of the page. Use the event to make final changes to the contents of the page or its controls before the rendering stage begins. PreRenderComplete Raised after each data bound control whose DataSourceID property is set calls its DataBind method. For more information, see Data Binding Events for Data-Bound Controls later in this topic. SaveStateComplete Raised after view state and control state have been saved for the page and for all controls. Any changes to the page or controls at this point affect rendering, but the changes will not be retrieved on the next postback. Render This is not an event; instead, at this stage of processing, the Page object calls this method on each control. All ASP.NET Web server controls have a Render method that writes out the control's markup to send to the browser. If you create a custom control, you typically override this method to output the control's markup. However, if your custom control incorporates only standard ASP.NET Web server controls and no custom markup, you do not need to override the Render method. For more information, see Developing Custom ASP.NET Server Controls. A user control (an .ascx file) automatically incorporates rendering, so you do not need to explicitly render the control in code. Unload Raised for each control and then for the page. In controls, use this event to do final cleanup for specific controls, such as closing control-specific database connections. For the page itself, use this event to do final cleanup work, such as closing open files and database connections, or finishing up logging or other request-specific tasks.

DOTNET Interview Questions part-7

1.  And if they have conflicting method names?
It’s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you’re okay.

2.  What’s the difference between an interface and abstract class?
In the interface all methods must be abstract, in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes.

3.  How can you overload a method?
Different parameter data types, different number of parameters, different order of parameters.

4.  If a base class has a bunch of overloaded constructors, and an inherited class has another bunch of overloaded constructors, can you enforce a call from an inherited constructor to an arbitrary base constructor?
Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.

5.  What’s the difference between System.String and System.StringBuilder classes?
System.String is immutable, System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

6.  Is it namespace class or class namespace?
The .NET class library is organized into namespaces. Each namespace contains a functionally related group of classes so natural namespace comes first. 

DOTNET Interview Questions part-6

1.  What does the keyword virtual mean in the method definition?
The method can be over-ridden.

2.  Can you declare the override method static while the original method is non-static?
No, you can’t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.

3.  Can you override private virtual methods?
No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.

4.  Can you prevent your class from being inherited and becoming a base class for some other classes?
Yes, that’s what keyword sealed in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class WhateverBaseClassName. It’s the same concept as final class in Java.

5.  Can you allow class to be inherited, but prevent the method from being over-ridden?
Yes, just leave the class public and make the method sealed.

6.  What’s an abstract class?
A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden. Essentially, it’s a blueprint for a class without any implementation.

7.  When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)?
When at least one of the methods in the class is abstract. When the class itself is inherited from an abstract class, but not all base abstract methods have been over-ridden.

8.  What’s an interface class?
It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.

9.  Why can’t you specify the accessibility modifier for methods inside the interface?
They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it’s public by default.

10.Can you inherit multiple interfaces?
Yes, why not.

DOTNET Interview Questions part-5

1.What is a pre-requisite for connection pooling?
Multiple processes must agree that they will share the same connection, where every parameter is the same, including the security settings.

2.What’s the implicit name of the parameter that gets passed into the class’ set method?
Value, and it’s datatype depends on whatever variable we’re changing.

3. How do you inherit from a class in C#?
Place a colon and then the name of the base class.

4.Does C# support multiple inheritance?
No, use interfaces instead.

5.When you inherit a protected class-level variable, who is it available to?
Classes in the same namespace.

6.Are private class-level variables inherited?
Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.

7.Describe the accessibility modifier protected internal.
It’s available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).

8.C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write?

   Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there’s no implementation in it.

9.What’s the top .NET class that everything is derived from?
System.Object.

10.How’s method overriding different from overloading?
When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.

DOTNET Interview Questions part-4

1. What are advantages and disadvantages of Microsoft-provided data provider classes in ADO.NET?
SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and Informix, but it’s a .NET layer on top of OLE layer, so not the fastest thing in the world. ODBC.NET is a deprecated layer provided for backward compatibility to ODBC engines.

2.What’s the role of the DataReader class in ADO.NET connections?
It returns a read-only dataset from the data source when the command is executed.

3.What is the wildcard character in SQL?
Let’s say you want to query database with LIKE for all employees whose name starts with La. The wildcard character is %, the proper query with LIKE would involve ‘La%’.

4.Explain ACID rule of thumb for transactions.
Transaction must be Atomic (it is one unit of work and does not dependent on previous and following transactions), Consistent (data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t), Isolated (no transaction sees the intermediate results of the current transaction), Durable (the values persist if the data had been committed even if the system crashes right after).

5.What connections does Microsoft SQL Server support?
Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords).

6.Which one is trusted and which one is untrusted?
Windows Authentication is trusted because the username and password are checked with the Active Directory, the SQL Server authentication is untrusted, since SQL Server is the only verifier participating in the transaction.

7.Why would you use untrusted verificaion?
Web Services might use it, as well as non-Windows applications.

8.What does the parameter Initial Catalog define inside Connection String?
The database name to connect to.

9.What’s the data provider name to connect to Access database?
Microsoft.Access.

10.What does Dispose method do with the connection object?
Deletes it from the memory.

DOTNET Interview Questions part-3

1.What debugging tools come with the .NET SDK?
CorDBG – command-line debugger, and DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR. To use CorDbg, you must compile the original C# file using the /debug switch.

2. What does the This window show in the debugger?
It points to the object that’s pointed to by this reference. Object’s instance data is shown.

3. What does assert() do?
In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. The program proceeds without any interruption if the condition is true.

4.What’s the difference between the Debug class and Trace class?
Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release builds.

5.Why are there five tracing levels in System.Diagnostics.TraceSwitcher?
The tracing dumps can be quite verbose and for some applications that are constantly running you run the risk of overloading the machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing activities.

6.Where is the output of TextWriterTraceListener redirected?
To the Console or a text file depending on the parameter passed to the constructor.

7.How do you debug an ASP.NET Web application?
Attach the aspnet_wp.exe process to the DbgClr debugger.

8.What are three test cases you should go through in unit testing?
Positive test cases (correct data, correct output), negative test cases (broken or missing data, proper handling), exception test cases (exceptions are thrown and caught properly).

9.Can you change the value of a variable while debugging a C# application?
Yes, if you are debugging via Visual Studio.NET, just go to Immediate window.

10.Explain the three services model (three-tier application).
Presentation (UI), business (logic and underlying code) and data (from storage or other sources).

DOTNET Interview Questions part-2

1.  What’s a delegate?
A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.

2.  What’s a multicast delegate?
It’s a delegate that points to and eventually fires off several methods.

3.  How’s the DLL Hell problem solved in .NET?
Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32), but also the version of the assembly.

4.  What are the ways to deploy an assembly? 
    An MSI installer, a CAB archive, and XCOPY command.

5.  What’s a satellite assembly?
When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies.

6.  What namespaces are necessary to create a localized application?
System.Globalization, System.Resources.

7.  What’s the difference between // comments, /* */ comments and /// comments?
Single-line, multi-line and XML documentation comments.

8.  How do you generate documentation from the C# file commented properly with a command-line compiler?
Compile it with a /doc switch.

9.  What’s the difference between <c> and <code> XML documentation tag?
Single line code example and multiple-line code example.

10.Is XML case-sensitive?
Yes, so <Student> and <student> are different elements.

DOTNET Interview Questions part-1

1.  What's the advantage of using System.Text.StringBuilder over System.String?
StringBuilder is more efficient in the cases, where a lot of manipulation is done to the text. Strings are immutable, so each time it’s being operated on, a new instance is created.

2.  Can you store multiple data types in System.Array?
No.

3.  What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
The first one performs a deep copy of the array, the second one is shallow.

4.  How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.

5.  What’s the .NET datatype that allows the retrieval of data by a unique key?
HashTable.

6.  What’s class SortedList underneath?
A sorted HashTable.

7.  Will finally block get executed if the exception had not occurred?
Yes.

8.  What’s the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception?
A catch block that catches the exception of type System.Exception. You can also omit the parameter data type in this case and just write catch {}.

9.  Can multiple catch blocks be executed?
No, once the proper catch code fires off, the control is transferred to the finally block (if there are any), and then whatever follows the finally block.

10.Why is it a bad idea to throw your own exceptions?
Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies some design flaws in the project.