ASP.NET controls(Server control,Html control ,Validation Control) - contributed by Nihal Singh

Life Cycle of an ASP.NET Web Page

The life cycle starts when a user requests a Web page through the browser. The Web server then processes the page through the step by step events before returning the results back to the user’s browser. These processing stages define the life cycle of a Web page.

Page Life Cycle Events

Understanding View State

The HTTP protocol is a stateless protocol. Each time user request a web page from a website, from the website’s perspective, you are a completely new person. View state persist state across postbacks. For example, if you assign a value to a Label control’s Text property, the Label control retains this value across multiple page requests. It is a hidden form field named __VIEWSTATE. This hidden form field contains the value of the control’s property. When the page is posted back to the server, the ASP.NET Framework gets the values of all the properties stored in View State. In this way, the ASP.NET Framework preserves the state of control properties across postbacks to the web server. By default, View State is enabled for every control.

The __VIEWSTATE hidden form field can become very large. Storing too much data into View State can slow down the rendering of a page because the contents of the hidden field must be pushed back and forth between the web server and browser.

You can see how much View State each control contained in a page is consuming by enabling tracing for a page by applying Trace=”true” attribute in its <%@ Page %> directive, which enables tracing.

Understanding the Page.IsPostBack Property

The Page class includes a property called the IsPostBack property, which you can use to detect whether the page has already been posted back to the server. Its return type is bool.Page load event is fire every time when you request a page through the firing of event or some other ways. So if you have done some coding in Page_Load event, it will be initializing every time. If you remove the IsPostBack property from the Page_Load() method, then you will not get the desire result. The DropDownList always displays its first item as the selected item.

Example

public partial class _Default : System.Web.UI.Page
{
              protected void Page_Load(object sender, EventArgs e)
              {
                            if (!Page.IsPostBack)
                            {
                                          // create collection of items
                                          ArrayList items = new ArrayList();
                                          items.Add(“ASP.NET”);
                                          items.Add(“C#”);
                                          items.Add(“VB.NET”);

                                          // Bind to DropDownList
                                          DropDownList1.DataSource = items;
                                          DropDownList1.DataBind ();
                            }
              }

              protected void Button1_Click(object sender, EventArgs e)
              {
                            Label1.Text = DropDownList1.SelectedItem.Text;
              }

}

Input Validation

Validation is important part of any web application. Validation controls provide Rapid Application Development (RAD) features for automatically checking the validity of input data. These controls are available in the System.Web.UI.WebControls namespace.

Validation controls are used to:

• To validate user input data.
• Data format, data type and data range is used for validation.

Six validation controls are available in the ASP.NET

RequiredFieldValidator : Enables you to require a user to enter a value in a form field.
RangeValidator : Enables you to check whether a value falls between a certain minimum and maximum value
CompareValidator : Enables you to compare a value against another value or perform a data type check.
RegularExpressionValidator : Enables you to compare a value against a regular expression.
CustomValidator : Enables you to perform custom validation.
ValidationSummary : Enables you to display a summary of all validation errors in a page.

RequiredFieldValidator

You can create a field as a mandatory field by adding a RequiredFieldValidator control to the page and linking it to the required control. For example, you can specify that users must fill in a Name text box before they can submit a registration form.

Example:

<asp: Textbox id="txtName" runat="server"></asp: Textbox>
<asp: RequiredFieldValidator id="RequiredFieldValidator1" runat="server" ControlToValidate="txtName" ErrorMessage="Name is a required field."
ForeColor="Red">
</asp: RequiredFieldValidator>

CompareValidator

You can perform three different types of validation tasks by using CompareValidator control.

• To perform a data type check.
• To compare the value entered into a form field against a fixed value.
• To compare the value of one form field against another

Example

<asp: Textbox id="txtAge" runat="server"></asp: Textbox>

<asp: CompareValidator id="CompareFieldValidator1" runat="server"
ForeColor="Red"
ControlToValidate="txtAge"
ValueToCompare="0"
Type="Integer"
Operator="GreaterThanEqual"
ErrorMessage="Please enter number greater than zero.">
</asp: CompareValidator >

RangeValidator

The RangeValidator control provides the facility to check whether the value of a form field falls between a certain minimum and maximum value. It verifies that user input is within a specified range of values.

Example

<asp: Textbox id="TextBox1"
runat="server"/>
<asp: RangeValidator id="Range1"
ControlToValidate="TextBox1"
MinimumValue="1"
MaximumValue="10"
Type="Integer"
EnableClientScript="false"
Text="The value must be from 1 to 10!"
runat="server"/>

Don’t forget to set the Type property when using the RangeValidator control. By default, the Type property has the value String, and the RangeValidator performs a string comparison to determine whether a values falls between the minimum and maximum value.

RegularExpressionValidator

The RegularExpressionValidator control performs its validation according to the regular expression. A regular expression is a powerful pattern-matching language that can be used to identify simple and complex character sequences. You can check a predefined pattern, such as a phone number, postal code, e-mail address, dates, and so on. The control uses the ValidationExpression property to set a valid regular expression
that is applied to the data that is to be validated.

Example

<asp:RegularExpressionValidator
id=”regEmail”
ControlToValidate=”txtEmail”
Text=” (Invalid email)”
ValidationExpression=”\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*
Runat=”server” />

ValidationSummary

The ValidationSummary control allows you to summarize the error messages from all validation controls on a Web page in a single location. This control is particularly useful when working with large forms.
If a user enters the wrong value for a form field located toward the end of the page, then the user might never see the error message. If you use the ValidationSummary control, however, you can always display a list of errors at the top of the form.

CustomValidator

CustomValidator control enables you to create your own validation and that validation can run with the other validation control on the page. The CustomValidator control performs validation-based code you write. You can write validation code that will be executed on the client side using JavaScript,or with server-side validation .

Custom Client-Side Validation

Client-side validation provides users immediate feedback when they are working with your page.

STEPS:

Define a JavaScript function.The function must have the following method signature:

function MyFuction(source, arguments)

// MyFuction is the user defined function name.

Attach your client-side function to a CustomValidator by setting the ClientValidationFunction property of the CustomValidator control to the name of your validation function.

Example:

//Code for Password must be between 6-12 characters

<script language="javascript" type="text/javascript">

function MyFuction (source, arguments)
{
              var data = arguments.Value.split('');
              //start by setting false
              arguments.IsValid=false;
              //check length
              if(data.length < 6 || data.length > 12) return;
                            arguments.IsValid=true;
}

</script>

Custom Server-Side Validation

If you want to work with CustomValidator control you must override its ServerValidate event.

Example:

protected void CustomValidatorNewPassword_ServerValidate(object source, ServerValidateEventArgs args)
{
              string data = args.Value;
              //start by setting false
              args.IsValid = false;
              //check length
              if (data.Length < 6 || data.Length > 12) return;
                            args.IsValid = true;
}