How to call jQuery code only before the ASP.NET postback

"PostBack is the name given to the process of submitting an ASP.NET page to the server for processing ."

protected void Page_Load(object sender, EventArgs e)

{

   if (IsPostBack)

   {

        ClientScript.RegisterHiddenField("hdnPostBack", "1");

   }

 }




$(document).ready(function () {

    var isPostBackOccured = document.getElementById('hdnPostBack');

    if (isPostBackOccured== null) alert('Page is called first Time');

    else alert('Page is called after Postback');

});

3 Tier Login Example

UI:
Login Page
public partial class login : System.Web.UI.Page
{
businessLogic obj = new businessLogic();

protected void button_Click(object sender, EventArgs e)
{
obj.Username = username.Text;
obj.Password = password.Text;
obj.loginbll();
Response.Redirect("HOme.aspx");
}
}

BLL:

using databaselogic;
public class businessLogic
{

public businessLogic ()
{
databaselogic obj_Bl = new databaselogic();

}
public string _username, _password;

public string Username
{
get { return _username; }
set { _username = value; }
}

public string Password
{
get { return _password; }
set { _password = value; }
}

public void loginbll()
{

obj_Bl.login(Username,Password);

}


DAL:

namespace databaselogic
{

public class databaselogic
{
public databaselogic()
{
}
public void login(string username, string password)
{
//code related to Queries goes on here
}
}
}

OOPS and examples

All the programming languages supporting Object oriented Programming will be supporting these three main concepts:
1. Encapsulation
2. Inheritance
3. Polymorphism

Encapsulation in C#:

Encapsulation is process of keeping data and methods together inside objects. In this way developer must define some methods of object?s interaction. In C# , encapsulation is realized through the classes. A Class can contain data structures and methods. Consider the following class.

public class Aperture
{
public Aperture()
{

}

protected double height;
protected double width;
protected double thickness;

public double GetVolume()
{
double volume = height*width*thickness;
if(volume<0)
return 0;
return volume;
}
}

In this example we encapsulate some data such as height, width, thickness and method GetVolume. Other methods or objects can interact with this object through methods that have public access modifier. It must be done using ?.? operator.

Inheritance in C#:

In a few words, Inheritance is the process of creation new classes from already existing classes. The inheritance feature allows us to reuse some parts of code. So, now we have some derived class that inherits base class?s members. Consider the following code snippet:

public class Door : Aperture
{
public Door() : base()
{

}

public bool isOutside = true;
}

As you see to inherit one class from another, we need to write base class name after ?:? symbol. Next thing that was done in code Door () ? constructor also inherits base class constructor. And at last we add new private field. All members of Aperture class are also in Door class. We can inherit all the members that has access modifier higher than protected.

Polymorphism in C#:

Polymorphism is possibility to change behavior with objects depending of object?s data type. In C# polymorphism realizes through the using of keyword virtual and override. Let look on the example of code:

public virtual void Out()
{
Console.WriteLine("Aperture virtual method called");
} 
//This method is defined in Aperture class. 
public override void Out()
{
Console.WriteLine("Door virtual method called");
}


Now we need to re-define it in our derived Door class. The usage of virtual methods can be clarified when we creating an instance of derived class from the base class:
Aperture ap = new Door();
ap.Out();