Why we use Static Keyword?

The static keyword defines, that the class or property or method we declare as static does not require a previous instance of an object. In the other hand, a static method for example cannot use any instance method / instance property of the own object.

Also static defined things will be optimized by the compiler, for example that a static object is only written once in the memory and everything accesses to the same object. When we use static keyword it means there is no need to create an instance of object . Static class including a static method can called by class name. Static class can have only static methods.

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Why .NET

Few points to answer why .NET

1.   In .NET we have language choice to code with (C#,VB.NET, Java,Boo,Python e.t.c), producing the same type of compiled code.
2.  .NET programs run at native speed while java is interpreted which makes java slower.Although java has Just In Time compilation but it stills run slower. With .NET you are not limited to JIT but have the option for AOT(Ahead of time) compilation if you want to eliminate startup delays.
3. Calling native code in java is not a very clean process. You need to generate some stub files which makes the whole process cumbersome and dirty. In .NET you just declare that you are calling a native function from a specified library and just start calling it. 
4. .NET languages are richer than Java. They have object oriented feature that are absent in java e.g properties,delegates,generics.
5.  Java GUI programs look alien on the host operating system. Even if you use the OS's theme you still notice that the java widgets look out of place.
6.  .NET in the form of Mono has brought a whole revolution on the linux desktop in form of great applications like beagle, tomboy, diva, iFolder, banshee e.t.c. This is something that java has failed to do despite the fact that it's been there long before .NET
7. Many programs that would have been difficult to develop with java have been developed with .NET things like compilers (Mono's C# and VB.NET) 3D game engines (unity game engine) e.t.c
8.  The CLI is an open standard maintained by an independent standards organization (E.C.M.A) while java is still governed by SUN microsystems.Even though java has recently been open-sourced, it's future will still be highly influenced by SUN.
9. You can code on the .NET platform using Java but you cannot code on Java platform using any of the .NET languages.

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How to use Ajax calendar in ASP.NET

Step 1: Register ajax dll

Add this line after @Page directive.
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="ajaxtoolkit" %>

Step 2 : Include scriptmanager in your code
 <asp:ScriptManager ID="scrp" runat="server">    </asp:ScriptManager>

Step 3 : Next
<asp:TextBox ID="txtDOB" runat="server" />
                                                        <asp:Image ID="imgDOB" runat="server" Height="22px" ImageUrl="~/images/calendar.JPG"
                                                            Width="26px" />
                                                        <ajaxtoolkit:CalendarExtender ID="calDOB" runat="server" PopupButtonID="imgDOB" TargetControlID="txtDOB">
                                                        </ajaxtoolkit:CalendarExtender>

Ajax calendar control has two main properties, PopupButtonID and TargetControlID.

When we click on the image button a calendar will be shown and selected date will be displayed in textbox.

For this to work you need to add AjaxControlToolKit dll.

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PageIndexChanging Vs PageIndexChanged

PageIndexChanging
- Occurs when one of the pager buttons is clicked, but before the GridView control handles the paging operation. This event is often used to cancel the paging operation. 
Ex:
protected void gvTeachers_PageIndexChanging(object sender, GridViewPageEventArgs e)
        {
            try
            {
                gvTeachers.PageIndex = e.NewPageIndex;
               //bind the grid
            }
            catch (Exception ex)
            {
                lblErrorMessage.Visible = true;
                lblErrorMessage.Text = ex.Message;
                log.Error(ex.Message + " "+ex.StackTrace);
            }
        }


PageIndexChanged
- Occurs when one of the pager buttons is clicked, but after the GridView control handles the paging operation. This event is commonly used when you need to perform a task after the user navigates to a different page in the control.

PageIndexChanged is fired after the actual page index is changed, but before the GridView is databound again with the new page data.
PageIndexChanging fired prior to the change and the PageIndexChanged fired after the new data for the next page is displayed. 

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Event Handling in ASP.NET

Event is an action or occurrence like mouse click, key press, mouse movements, or any system generated notification. The processes communicate through events. For example, Interrupts are system generated events. When events occur the application should be able to respond to it.

In ASP.Net an event is raised on the client, and handled in the server. For example, a user clicks a button displayed in the browser. A Click event is raised. The browser handles this client-side event by posting it to the server.

The server has a subroutine describing what to do when the event is raised; it is called the event-handler. Therefore, when the event message is transmitted to the server, it checks whether the Click event has an associated event handler, and if it has, the event handler is executed.

All ASP.Net controls are implemented as classes, and they have events which are fired when user performs certain action on them. For example, when a user clicks a button the 'Click' event is generated. For handling these events there are in-built attributes and event handlers. To respond to an event, the event handler is coded

The common control events.

Event	Attribute	Controls
Click	OnClick	Button, image button, link button, image map
Command	OnCommand	Button, image button, link button
TextChanged	OnTextChanged	Text box
SelectedIndexChanged	OnSelectedIndexChanged	Drop-down list, list box, radio button list, check box list.
CheckedChanged	OnCheckedChanged	Check box, radio button

Some events cause the form to be posted back to the server immediately, these are called the postback events. For example, the click events like, Button.Click. Some events are not posted back to the server immediately, these are called non-postback events.For example, the change events or selection events, such as, TextBox.TextChanged or CheckBox.CheckedChanged, or DropDownList,SelectedIndexChanged.The nonpostback events could be made to post back immediately by setting their AutoPostBack property to true.

The default event for the Page object is the Load event. Similarly every control has a default event. For example, default event for the button control is the Click event.

The default event handler could be created in Visual Studio, just by double clicking the control in design view.

Common Page and Control Events

• DataBinding . raised when a control bind to a data source
• Disposed . when the page or the control is released
• Error . it is an page event, occurs when an unhandled exception is thrown
• Init . raised when the page or the control is initialized
• Load . raised when the page or a control is loaded
• PreRender . raised when the page or the control is to be rendered
• Unload . raised when the page or control is unloaded from memory

Application and Session Events

The most important application events are:

• Application_Start . it is raised when the application/website is started
• Application_End . it is raised when the application/website is stopped

Similarly, the most used Session events are:

• Session_Start . it is raised when a user first requests a page from the application
• Session_End . it is raised when the session ends
  
  

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