What is viewstate

In this video session, we will learn about
1. Stateless nature of HTTP protocol
2. How a webform is processed
3. What is ViewState
4. The role of ViewState in ASP.NET
5. Primary difference between ASP.NET Server controls and HTML controls

Web Applications work on HTTP protocol. HTTP protocol is a stateless protocol, meaning it does not retain state between user requests. Let's understand the stateless nature of the HTTP protocol with an example.

Create a new asp.net web application project. Drag and drop a TextBox and a Button control onto the webform. Change the Text property of the Button control to Click Me.

At this point, double click the button control, which should generate the event handler in the code behind file. Modify the code behind file, so the code in WebForm1 class looks as shown below. 
1. In the scope of WebForm1 class, we are creating an integer variable ClicksCount which is initialized to ZERO.
2. On the Page_Load() event handler, we are setting the Text property of TextBox1 to ZERO. We do this initialization, only, when the request is an initial GET request.
3. In the Button1_Click() event, we are incrementing the value of the ClicksCount by 1, and then assigning the value to the Text property of TextBox1.
public partial class WebForm1 : System.Web.UI.Page
{
    int ClicksCount = 0;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            TextBox1.Text = "0";
        }
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        ClicksCount = ClicksCount + 1;
        TextBox1.Text = ClicksCount.ToString();
    }
}

With this code in place, run the application, and click the Button. We expect the count to be increased every time we click the button. When you click it the first time, it gets incremented to 1. After that, no matter how many times you click it, the value stays at 1. This is because of the stateless nature of the web applications that work on HTTP protocol.



So what actually happens when you make a GET request for this WebForm1?
When we compile this project an assembly is generated. Since the name of the project is ViewStateDemo, the name of the assembly will be ViewStateDemo.dll. So when a request is made for WebForm1, The application's assembly(ViewStateDemo.dll) creates an instance (object), of WebForm1, initializes ClicksCount to ZERO, and set's the TextBox1.Text to ZERO. As this is the initial GET request, the Button1_Click() event will not be executed. At this point the web server, generates the HTML to respond to the request, and posts that response back to the browser. It then immediately destroys the instance of the WebForm1.

The browser receives the HTML, and we should now see textbox set to ZERO.

What happens when we click the Button on WebForm1?
When we click the Button, the WebForm1 gets posted to the server. This is a PostBack request, NOT A GET REQUEST. So, when the webform is posted back, a new instance of this webform is created again, initializing the ClicksCount variable to ZERO. This time, the code that is wrapped between IF(!ISPOSTBACK) block is not executed. Button1_Click() event gets executed as this is a PostBack event. ClicksCount is incremented from 0 to 1. The value is then assigned to the Text Property of TextBox1. Generates the HTML, sends it to client and destroys the webform.

At this Point, we should see the value increased to 1.

What happens when we click the Button on WebForm1 again?
When you click the button for the second time, the webform gets posted back again. A new instance of WebForm1 is created. ClicksCount initialized to ZERO. In the Button1_Click() event, the value gets incremented to 1 and assigned to TextBox1. HTML gets generated and sends it to client and destroys the webform.

So, no matter how many times you click the Button, the value of the TextBox, will not move beyond 1.

Now, let's see, how to preserve the state between requests using ViewState variables. Re-write the code in WebForm1, as shown below.
public partial class WebForm1 : System.Web.UI.Page
{
    int ClicksCount = 1;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            TextBox1.Text = "0";
        }
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        if(ViewState["Clicks"] != null)
        {
            ClicksCount = (int)ViewState["Clicks"] + 1;
        }
        TextBox1.Text = ClicksCount.ToString(); ;
        ViewState["Clicks"] = ClicksCount;
    }
}



Click the Button now, and the value gets incremented every time we click. So how is this possible now. It's possible because, we are using the ViewState variable Clicks to preserve the data between requests. The ViewState data, travels with every request and response between the client and the web server.

Now, let's try to achieve the same behaviour, without explicitly storing data in a ViewState variable. Modify the WebForm1 code as shown below.
public partial class WebForm1 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            TextBox1.Text = "0";
        }
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        int ClicksCount = Convert.ToInt32(TextBox1.Text) + 1;
        TextBox1.Text = ClicksCount.ToString(); 
    }
}

Upon clicking the Button, the value gets incremented correctly as expected. This is possible because, TextBox1 is an asp.net server control, that uses viewstate internally, to preserve data across postbacks.

Because Web forms have very short lifetimes, ASP.NET takes special steps to preserve the data entered in the controls on a Web form. Data entered in controls is sent with each request and restored to controls in Page_Init. The data in these controls is then available in the Page_Load(), Button_Click(), and many more events, that occur after Page_Init() event. We will discuss about, all the events in the life cycle of a webform and the order in which they occur in a later video session.

On the other hand the HTML controls, do not retain state across post backs. Only ASP.NET server controls retains state. To prove this
1. Add a new webform to the web application project
2. Drag and Drop Input(Text) control from the HTML tab, in the ToolBox
3. Drag and Drop TextBox control from the Standard tab, in the ToolBox
4. Finally drag and drop a button
5. Set the newly added webform as the start page by right clicking on it, in the solution explorer
6. Run the project, by pressing CTRL + F5
7. Type "TEST" into both the controls (ASP.NET TextBox and the HTML TextBox), and press the button
8. You should see that, the value in the ASP.NET TextBox is preserved across postback, but not the value in the standard HTML textbox

An HTML control can be converted in ASP.NET server control, by adding runat="server" attribute in the HTML source as shown below.
<input id="Text1" runat = "server" type="text" />

Now, if you type TEST and click the button, both controls now retain state across postback.

ViewState data is serialized into base64-encoded strings, and is stored in Hidden input field __ViewState. To view this hidden input field, right click on the browser and select "View Page Source" for google chrome. In internet explorer, right click and select "View Source"

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Creating your first ASP.NET website

In this video session
1. We will learn about using visual studio
2. Creating your first ASP.NET web application
3. Learn about different windows in visual studio

Start Page in Visual Studio:
When you first run visual studio, you will see the start page. The start page contains latest news related to .NET development, learning and community resources. If you are using visual studio 2010, at the bottom of the start page, you will notice the following 2 options.
1. Close page after project load - Select this option if you want to close the start page, as soon as you open and load a project.
2. Show page on startup - Uncheck this option, if you don't want the start page to be shown, when you start visual studio.

If you have closed the start page, and later, if you want to see it again, select START PAGE from the VIEW menu.

Creating your first ASP.NET web application:
1. Select File => New Project
2. Select the Programming language you want to use from Installed Templates section, in the New Project dialog box. Out of the box, you can either use C# or Visual Basic to develop ASP.NET web applications.
3. Now, Select ASP.NET Web Application, from the middle section of the New Project dialog box.
4. Give your project and solution a meaningful name.
5. Select the location, where you want the solution to be created.
6. Finally click OK.




Different windows in visual studio:
At this point, you should have your first web application created. Now, let's shift our focus, to learn more about the windows that we see in visual studio.

Solution Explorer: To view the solution explorer window, from the VIEW menu, select SOLUTION EXPLORER. Or you can also use keyboard short cut, CTRL + W, S. On the solution explorer, use the AUTO-HIDE push pin button, to either show or hide solution explorer.


Visual Studio organizes applications into projects and solutions. A solution is a collection of projects. In our example, we have WebApplication2 solution. This solution has only one project - WebApplication2. If you want to add another project to the solution, simply right click the solution, and Select Add => New Project. For example, to add a class library project, select CLASS LIBRARY from the New Project dialog box and click OK.

At this point, your solution should contain 2 projects
1. A web Application Project - WebApplication2
2. A class library project - ClassLibrary1




Notice that, in the solution explorer, WebApplication2 project is bolded, indicating that this is the start up project. You can only have one start up project in a solution. If you want to change your start up project, RIGHT CLICK the project, and select "SET AS STARTUP PROJECT". The start-up project is the project that runs when you click Start in Visual Studio .NET. When you’re developing multiple projects as part of a single solution, the start-up project usually calls the other projects in the solution.

The solution file will have a .sln extension and the project file will have .csproj (if c# is the programming language) or .vbproj (if visual basic is the programming language)

Tool Box: To view the TOOL BOX, Select TOOL BOX from the VIEW menu, or use the keyboard short cut, CTRL + W, X. Just like, solution explorer, tool box can be auto hidden using the AUTO-HIDE PUSH PIN. Toolbox displays the controls and components that can be used on a web form.

Web Forms: WebForms has the extension of .aspx. A web form also has a code behind and designer files. Code behind files has the extension of .aspx.cs (if c# is the programming language) or .aspx.vb (if vb is the programming language). Designer files contains the extension of .aspx.designer.cs (if c# is the programming language) or .aspx.designer.vb (if visual basic is the programming language). Code behind files contain the code that user writes, where as the designer file contains the auto generated code. You shouldn't change the code in the designer file, because that code might later be modified by Visual Studio and your changes could be overwritten. A Web form is associated with its code file using the @Page directive found in the Web form’s HTML.
<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="WebApplication2._Default" %>

A webform's HTML can be edited either in Source or Design mode. You can also choose SPLIT mode, which shows both the DESIGN and the SOURCE at the same time.


Properties Window: Used to change property of a webform or a control on a webform. To view the Properties window, select PROPERTIES WINDOW from the VIEW menu, or use keyboard short cut CTRL + W, P.

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What is ASP.NET

ASP.NET is a Web application framework developed by Microsoft to build dynamic data driven Web applications and Web services. 
1. ASP.NET is a subset of .NET framework. In simple terms a framework is a collection of classes. 
2. ASP.NET is the successor to classic ASP (Active Server Pages).

What other technologies can be used to build web applications
1. PHP
2. Java
3. CGI
4. Ruby on Rails
5. Perl



What is a Web Application?
A web application is an application that is accessed by users using a web browser. Examples of web browsers include 
1. Microsoft Internet Explorer
2. Google Chrome
3. Mozilla FireFox
4. Apple Safari
5. Netscape Navigator

What are the advantages of Web applications?
1. Web Applications just need to be installed only on the web server, where as desktop applications need to be installed on every computer, where you want to access them.
2. Maintenance, support and patches are easier to provide.
3. Only a browser is required on the client machine to access a web application.
4. Accessible from anywhere, provided there is internet.
5. Cross Platform



How Web applications work?
1. Web applications work on client/server architecture
2. On the client all you need is a browser, that can understand HTML
3. On the server side, the Web application runs under Microsoft Internet Information Services (IIS)



When the client enters the URL of the web application in the browser, and submits the request. The web server which hosts the web application, receives the request. The request is then processed by the application. The application generates, the HTML and hands it over to the IIS (web server). Finally, IIS sends the generated HTML to the client, who made the initial request. The client browser will the interpret the HTML and displays the user interface. All this communication, happens over the internet using HTTP protocol. HTTP stands for Hyper Text Transfer Protocol. A protocol is a set of rules that govern how two or more items communicate.

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OLEDB Connection string

The C# OleDbConnection instance takes Connection String as argument and pass the value to the Constructor statement. An instance of the C# OleDbConnection class is supported the OLEDB Data Provider .

 connetionString = "Provider=Microsoft.Jet.OLEDB.4.0;
  Data Source=yourdatabasename.mdb;";
      

        cnn = new OleDbConnection(connetionString);

When the connection is established between C# application and the specified Data Source, SQL Commands will execute with the help of the Connection Object and retrieve or manipulate data in the database. Once the Database activities is over Connection should be closed and release from the data source resources .

 

  cnn.Close();

The Close() method in the OleDbConnection class is used to close the Database Connection. The Close method Rolls Back any pending transactions and releases the Connection from the Database connected by the OLEDB Data Provider.

 

 

using System;
using System.Windows.Forms;
using System.Data.OleDb; 

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string connetionString = null;
            OleDbConnection cnn ;
            connetionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=yourdatabasename.mdb;";
            cnn = new OleDbConnection(connetionString);
            try
            {
                cnn.Open();
                MessageBox.Show ("Connection Open ! ");
                cnn.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show("Can not open connection ! ");
            }
        }
    }
}

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C# ADO.NET SqlCommand - ExecuteScalar

The ExecuteScalar() in C# SqlCommand Object is using for retrieve a single value from Database after the execution of the SQL Statement. The ExecuteScalar() executes SQL statements as well as Stored Procedure and returned a scalar value on first column of first row in the returned Result Set.

 Command.ExecuteScalar();

The ExecuteNonQuery() performs Data Definition tasks as well as Data Manipulation tasks also. The Data Definition tasks like creating Stored Procedures ,Views etc. perform by the ExecuteNonQuery() . Also Data Manipulation tasks like Insert , Update , Delete etc. also perform by the ExecuteNonQuery() of SqlCommand Object.

If the Result Set contains more than one columns or rows , it will take only the value of first column of the first row, and all other values will ignore. If the Result Set is empty it will return a NULL reference.

It is very useful to use with aggregate functions like Count(*) or Sum() etc. When compare to ExecuteReader() , ExecuteScalar() uses fewer System resources.

The following C# example shows how to use the method ExecuteScalar() through SqlCommand Object.

using System;
using System.Windows.Forms;
using System.Data.SqlClient; 

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string connetionString = null;
            SqlConnection cnn ;
            SqlCommand cmd ;
            string sql = null;

            connetionString = "Data Source=ServerName;Initial Catalog=DatabaseName;User ID=UserName;Password=Password";
            sql = "Your SQL Statement Here like Select Count(*) from product";

            cnn = new SqlConnection(connetionString);
            try
            {
                cnn.Open();
                cmd = new SqlCommand(sql, cnn);
                Int32 count = Convert.ToInt32(cmd.ExecuteScalar());
                cmd.Dispose();
                cnn.Close();
                MessageBox.Show (" No. of Rows " + count);
            }
            catch (Exception ex)
            {
                MessageBox.Show("Can not open connection ! ");
            }
        }
    }
}

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C# ADO.NET SqlCommand - ExecuteNonQuery

The ExecuteNonQuery() is one of the most frequently used method in SqlCommand Object, and is used for executing statements that do not return result sets (ie. statements like insert data , update data etc.) .

 Command.ExecuteNonQuery();

The ExecuteNonQuery() performs Data Definition tasks as well as Data Manipulation tasks also. The Data Definition tasks like creating Stored Procedures ,Views etc. perform by the ExecuteNonQuery() . Also Data Manipulation tasks like Insert , Update , Delete etc. also perform by the ExecuteNonQuery() of SqlCommand Object.

The following C# example shows how to use the method ExecuteNonQuery() through SqlCommand Object.

using System;
using System.Windows.Forms;
using System.Data.SqlClient; 

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string connetionString = null;
            SqlConnection cnn ;
            SqlCommand cmd ;
            string sql = null;

            connetionString = "Data Source=ServerName;Initial Catalog=DatabaseName;User ID=UserName;Password=Password";
            sql = "Your SQL Statemnt Here";

            cnn = new SqlConnection(connetionString);
            try
            {
                cnn.Open();
                cmd = new SqlCommand(sql, cnn);
                cmd.ExecuteNonQuery();
                cmd.Dispose();
                cnn.Close();
                MessageBox.Show (" ExecuteNonQuery in SqlCommand executed !!");
            }
            catch (Exception ex)
            {
                MessageBox.Show("Can not open connection ! ");
            }
        }
    }
}

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C# ADO.NET SqlDataReader

SqlDataReader Object provides a connection oriented data access to the SQL Server data Sources from C# applications. ExecuteReader() in the SqlCommand Object sends the SQL statements to the SqlConnection Object and populate a SqlDataReader Object based on the SQL statement or Stored Procedures.

 
SqlDataReader sqlReader = sqlCmd.ExecuteReader();
  

When the ExecuteReader method in the SqlCommand Object execute , it will instantiate a SqlClient.SqlDataReader Object. When we started to read from a DataReader it should always be open and positioned prior to the first record. The Read() method in the DataReader is used to read the rows from DataReader and it always moves forward to a new valid row, if any row exist .

 
SqlDataReader.Read();
  

using System;
using System.Windows.Forms;
using System.Data.SqlClient; 

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string connetionString = null;
            SqlConnection sqlCnn ;
            SqlCommand sqlCmd ;
            string sql = null;

            connetionString = "Data Source=ServerName;Initial Catalog=DatabaseName;User ID=UserName;Password=Password";
            sql = "Your SQL Statement Here , like Select * from product";

            sqlCnn = new SqlConnection(connetionString);
            try
            {
                sqlCnn.Open();
                sqlCmd = new SqlCommand(sql, sqlCnn);
                SqlDataReader sqlReader = sqlCmd.ExecuteReader();
                while (sqlReader.Read())
                {
                    MessageBox.Show(sqlReader.GetValue(0) + " - " + sqlReader.GetValue(1) + " - " + sqlReader.GetValue(2));
                }
                sqlReader.Close();
                sqlCmd.Dispose();
                sqlCnn.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show("Can not open connection ! ");
            }
        }
    }
}

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C# ADO.NET SqlDataAdapter

SqlDataAdapter Class is a part of the C# ADO.NET Data Provider and it resides in the System.Data.SqlClient namespace. SqlDataAdapter provides the communication between the Dataset and the SQL database. We can use SqlDataAdapter Object in combination with Dataset Object. DataAdapter provides this combination by mapping Fill method, which changes the data in the DataSet to match the data in the data source, and Update, which changes the data in the data source to match the data in the DataSet.

 
 SqlDataAdapter adapter = new SqlDataAdapter();

  adapter.Fill(ds);
  

The SqlDataAdapter Object and DataSet objects are combine to perform both data access and data manipulation operations in the SQL Server Database. When the user perform the SQL operations like Select , Insert etc. in the data containing in the Dataset Object , it won't directly affect the Database, until the user invoke the Update method in the SqlDataAdapter.

using System;
using System.Windows.Forms;
using System.Data;
using System.Data.SqlClient; 

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string connetionString = null;
            SqlConnection sqlCnn ;
            SqlCommand sqlCmd ;
            SqlDataAdapter adapter = new SqlDataAdapter();
            DataSet ds = new DataSet();
            int i = 0;
            string sql = null;

            connetionString = "Data Source=ServerName;Initial Catalog=DatabaseName;User ID=UserName;Password=Password";
            sql = "Select * from product";

            sqlCnn = new SqlConnection(connetionString);
            try
            {
                sqlCnn.Open();
                sqlCmd = new SqlCommand(sql, sqlCnn);
                adapter.SelectCommand = sqlCmd;
                adapter.Fill(ds);
                for (i = 0; i <= ds.Tables[0].Rows.Count - 1; i++)
                {
                    MessageBox.Show(ds.Tables[0].Rows[i].ItemArray[0] + " -- " + ds.Tables[0].Rows[i].ItemArray[1]);
                }
                adapter.Dispose();
                sqlCmd.Dispose();
                sqlCnn.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show("Can not open connection ! ");
            }
        }
    }
}

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get the sql server version

 We can get the sql server version by using this query :

DECLARE @ver nvarchar(128);
SET @ver = CAST(serverproperty('ProductVersion') AS nvarchar);
SET @ver = SUBSTRING(@ver, 1, CHARINDEX('.', @ver) - 1)

IF ( @ver = '7' )
   SELECT 'SQL Server 7'
ELSE IF ( @ver = '8' )
   SELECT 'SQL Server 2000'
ELSE IF ( @ver = '9' )
   SELECT 'SQL Server 2005'
ELSE IF ( @ver = '10' )
   SELECT 'SQL Server 2008/2008 R2'
ELSE IF ( @ver = '11' )
   SELECT 'SQL Server 2012'
ELSE
SELECT 'Unsupported SQL Server Version'
  

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CCAvenue Payment Transaction Gateway in ASP.NET

INTRODUCTION

The CCAvenue Transaction Gateway offers e-merchants a one-stop solution for processing e- transactions ranging from credit ca rd transactions to direct debit from their online bank accounts.

The CCAvenue System has been designed for quick integration and ease of use.

The CCAvenue system expects certain input data with specific names to be sent to the CCAvenue website. For this reason, it is essential that the names of the input fields on the merchant’s web site and the CCAvenue.com web site match exactly. To achieve this the relevant data field values of the shopping cart must be assigned to the appropriate data field of the form provided below. Some of these input data fields are mandatory and marked in red, and must be sent to the CCAvenue system with every order. Please ensure that the values have no unnecessary blank spaces preceding or trailing the values.

  <form method="post" 
action="https://world.ccavenue.com/servlet/ccw.CCAvenueController"> 
   <input type="hidden" name="Merchant_Id" value="M_demos_17"> <%--Compulsory Field --This field represents the merchant id assigned to you by 
CCAvenue and identifies the order as one originating from your website. This field will accept up to a maximum of 20
characters only--%>
  <input type="hidden" name="Amount" value="1000"> /*Compulsory Field*/
  <input type=hidden name=Currency value="USD"> 
  <input type="hidden" name="Order_Id" value="ORD_ID1234"> <%--Compulsory Field
This field is a compulsory field that sends the id, which is to be the unique identifier for this order, to the CCAvenue site. This must be a unique id generated at your website and may contain combination of letters, numbers, dashes(-), forward slashes(/) or back slashes(\) up to a maximum of 30 characters. --%>
  <input type=hidden name=TxnType value="A"> 
  <input type=hidden name=actionID value="TXN"> 
  <input type="hidden" name="billing_cust_name" value="John"> 
  <input type="hidden" name="billing_middle_name" value="Edgar"> 
  <input type="hidden" name="billing_last_name" value="Doe"> 
  <input type="hidden" name="billing_cust_address" value="123 Green Acres, West Eden"> 
  <input type="hidden" name="billing_cust_city" value="Estberry"> 
  <input type="hidden" name="billing_cust_state" value="Wales">
  <input type="hidden" name="billing_cust_zip" value="12345"> 
  <input type="hidden" name="billing_cust_email" value="johndoe@hotmail.com"> 
  <input type="submit" value="Buy Now">          
 </form>
  

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