Introduction
In this section we will touch base on one of important concepts in ASP. NET.
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Following is the sequence in which the events occur:-
- Page_Init.
- Page Load.
- Control events
- Page- Unload event.
Page_init event only occurs when first time the page is started, but Page Load occurs in subsequent request of the page.
Page load event guarantees that all controls are fully loaded. Controls are also accessed in Page_Init events but you will see that view state is not fully loaded during this event.5
(B) How can we identify that the Page is Post Back?
Page object has an "IsPostBack" property, which can be checked to know that is the page posted back.
Refer Caching chapter.
Server controls like Data grid, Data List, and Repeater can have other child controls inside them. Example Data Grid can have combo box inside data grid. These child control do not raise there events by themselves, rather they pass the event to the container parent (which can be a data grid, data list, repeater), which passed to the page as "ItemCommand" event. As the child control send events to parent it is termed as event bubbling.
Page attributes are specified using the @Page directive.
Using the @Page directive and setting 'EnableViewStateMac' property to True.
@Register directive informs the compiler of any custom server control added to the page.
It's a feature provided by ASP. NET to prevent flickering and redrawing when the page is posted back.
Note:- This is only supported for IE browser. Project is who have browser compatibility as requirements have to think some other ways of avoiding flickering.
Web.config file defines configuration for a web project. Using "AppSetting" section, we can define user-defined values. Example below defined is "Connection String" section, which will be used through out the project for database connection.
<Configuration>
<appSettings>
<add key="ConnectionString" value="server=xyz;pwd=www;database=testing" />
</appSettings>
In HTML Hidden Fields.
It is used for caching. See more for Caching chapter.
User controls are created using .ASCX in ASP.NET. After .ASCX file is created you need to two things in order that the ASCX can be used in project:.
There are six main types of validation controls:-
RequiredFieldValidator
It checks whether the control have any value. It is used when you want the control should not be empty.
RangeValidator
It checks if the value in validated control is in that specific range. Example TxtCustomerCode should not be more than eight lengths.
CompareValidator
It checks that the value in controls should match some specific value. Example Textbox TxtPie should be equal to 3.14.
RegularExpressionValidator
When we want the control, value should match with a specific regular expression.
CustomValidator
It is used to define User Defined validation.
Validation Summary
It displays summary of all current validation errors on an ASP.NET page.
Note: - It is rare that some one will ask step by step all the validation controls. Rather they will ask for what type of validation which validator will be used. Example in one of the interviews i was asked how will you display summary of all errors in the validation control...just uttered one word Validation summary.
If we want the control to automatically post back in case of any event, we will need to check this attribute as true. Example on a Combo Box change we need to send the event immediately to the server side then set the "AutoPostBack" attribute to true.
Following are the points to be done in order to enable paging in Data grid:-
- Set the "Allow Paging" to true.
- In PageIndexChanged event set the current page index clicked.
Note: - The answers are very short, if you have implemented practically its just a revision. If you are fresher, just make sample code using Datagrid and try to implement this functionality.
It allows to execute ASP.NET application level events and setting application-level variables.
"Web.config" files apply settings to each web application, while "Machine.config" file apply settings to all ASP.NET applications.
Session object store information between HTTP requests for a particular user, while application object are global across users.