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# ASP.NET - Validation Controls

ASP.Net validation controls validate the user input data to ensure that useless, unauthenticated or contradictory data don.t get stored.

ASP.Net provides the following validation controls:

1. RequiredFieldValidator

2. RangeValidator

3. CompareValidator

4. RegularExpressionValidator

5. CustomValidator

6. ValidationSummary

# The BaseValidator Class:

The validation control classes inherit from the BaseValidator class and inherit its properties and methods. Therefore, it would help to take a look at the properties and the methods of this base class, which are common for all the validation controls:

Members | Description
--- | ---
ControlToValidate | Indicates the input control to validate.
Display | Indicates how the error message is shown.
EnableClientScript | Indicates whether client side validation will take.
Enabled | Enables or disables the validator.
ErrorMessage | Error string.
Text | Error text to be shown if validation fails.
IsValid | Indicates whether the value of the control is valid.
SetFocusOnError | It indicates whether in case of an invalid control, the focus should switch to the related input control.
ValidationGroup | The logical group of multiple validators, where this control belongs.
Validate() | This method revalidates the control and updates the IsValid property.

# The RequiredFieldValidator:

The RequiredFieldValidator control ensures that the required field is not empty. It is generally tied to a text box to force input into the text box.

The syntax for the control:

    <asp:RequiredFieldValidator ID="rfvcandidate"
            runat="server" ControlToValidate ="ddlcandidate"
            ErrorMessage="Please choose a candidate"
            InitialValue="Please choose a candidate">
    </asp:RequiredFieldValidator>

# The RangeValidator:

The RangeValidator control verifies that the input value falls within a predetermined range.

It has three specific properties:

Properties | Description
--- | ---
Type | it defines the type of the data; the available values are: Currency, Date, Double, Integer and String
MinimumValue | it specifies the minimum value of the range
MaximumValue | it specifies the maximum value of the range

The syntax for the control:

    <asp:RangeValidator ID="rvclass"
           runat="server"
           ControlToValidate="txtclass"
           ErrorMessage="Enter your class (6 - 12)"
           MaximumValue="12"
           MinimumValue="6" Type="Integer">
    </asp:RangeValidator>

# The CompareValidator:

The CompareValidator control compares a value in one control with a fixed value, or, a value in another control.

It has the following specific properties:

Properties | Description
--- | ---
Type | it specifies the data type
ControlToCompare | it specifies the value of the input control to compare with
ValueToCompare | it specifies the constant value to compare with
Operator | it specifies the comparison operator, the available values are: Equal, NotEqual, GreaterThan, GreaterThanEqual, LessThan, LessThanEqual and DataTypeCheck

The basic syntax for the control:

    <asp:CompareValidator ID="CompareValidator1"
            runat="server"
            ErrorMessage="CompareValidator">
    </asp:CompareValidator>

# The RegularExpressionValidator

The RegularExpressionValidator allows validating the input text by matching against a pattern against a regular expression. The regular expression is set in the ValidationExpression property.

The following table summarizes the commonly used syntax constructs for regular expressions:

Character Escapes | Description
--- | ---
\b | Matches a backspace
\t | Matches a tab
\r | Matches a carriage return
\v | Matches a vertical tab
\f | Matches a form feed
\n | Matches a new line
\ | Escape character

Apart from single character match, a class of characters could be specified that can be matched, called the metacharacters.

Metacharacters | Description
--- | ---
. | Matches any character except \n
[abcd] | Matches any character in the set
[^abcd] | Excludes any character in the set
[2-7a-mA-M] | Matches any character specified in the range
\w | Matches any alphanumeric character and underscore
\W | Matches any non-word character
\s | Matches whitespace characters like, space, tab, new line etc.
\S | Matches any non-whitespace character
\d | Matches any decimal character
\D | Matches any non-decimal character

Quantifiers could be added to specify number of times a character could appear

Quantifier | Description
--- | ---
* | Zero or more matches
+ | One or more matches
? | Zero or one matches
{N} | N matches
{N,} | N or more matches
{N,M} | Between N and M matches

The syntax for the control:

    <asp:RegularExpressionValidator ID="string"
            runat="server"
            ErrorMessage="string"
            ValidationExpression="string"
            ValidationGroup="string">
    </asp:RegularExpressionValidator>

# The CustomValidator:

The CustomValidator control allows writing application specific custom validation routines for both the client side and the server side validation.

The client side validation is accomplished through the ClientValidationFunction property. The client side validation routine should be written in a scripting language, like JavaScript or VBScript, which the browser can understand.

The server side validation routine must be called from the control.s ServerValidate event handler. The server side validation routine should be written in any .Net language, like C# or VB.Net.

The basic syntax for the control

    <asp:CustomValidator ID="CustomValidator1"
           runat="server"
           ClientValidationFunction=.cvf_func.
           ErrorMessage="CustomValidator">
    </asp:CustomValidator>

# The ValidationSummary Control

The ValidationSummary control does not perform any validation but shows a summary of all errors in the page. The summary displays the values of the ErrorMessage property of all validation controls that failed validation.

The following two mutually inclusive properties list out the error message:

- ShowSummary: shows the error messages in specified format.

- ShowMessageBox: shows the error messages in a separate window.

The syntax for the control:

    <asp:ValidationSummary ID="ValidationSummary1"
           runat="server"
           DisplayMode = "BulletList"
           ShowSummary = "true"
           HeaderText="Errors:" />

# Validation Groups:

Complex pages have different groups of information provided in different panels. In such a situation a need for performing validation separately for separate group, might arise. This kind of situation is handled using validation groups.

To create a validation group, you should put the input controls and the validation controls into the same logical group by setting their ValidationGroup property.

# Example:

The following example describes a form to be filled up by all the students of a school, divided into four houses, for electing the school president. We will be using the validation controls to validate the user input.

The form in Design view:

The content file code:

    <form id="form1" runat="server">
    <table style="width: 66%;">
    <tr>
    <td class="style1" colspan="3" align="center">
    <asp:Label ID="lblmsg"
               Text="President Election Form : Choose your president"
               runat="server" />
    </td>
    </tr>
    <tr>
    <td class="style3">
    Candidate:
    </td>
    <td class="style2">
    <asp:DropDownList ID="ddlcandidate" runat="server" Width="239px">
    <asp:ListItem>Please Choose a Candidate</asp:ListItem>
    <asp:ListItem>M H Kabir</asp:ListItem>
    <asp:ListItem>Steve Taylor</asp:ListItem>
    <asp:ListItem>John Abraham</asp:ListItem>
    <asp:ListItem>Venus Williams</asp:ListItem>
    </asp:DropDownList>
    </td>
    <td>
    <asp:RequiredFieldValidator ID="rfvcandidate"
           runat="server" ControlToValidate ="ddlcandidate"
           ErrorMessage="Please choose a candidate"
           InitialValue="Please choose a candidate">
    </asp:RequiredFieldValidator>
    </td>
    </tr>
    <tr>
    <td class="style3">
    House:</td>
    <td class="style2">
    <asp:RadioButtonList ID="rblhouse"
          runat="server"
          RepeatLayout="Flow">
    <asp:ListItem>Red</asp:ListItem>
    <asp:ListItem>Blue</asp:ListItem>
    <asp:ListItem>Yellow</asp:ListItem>
    <asp:ListItem>Green</asp:ListItem>
    </asp:RadioButtonList>
    </td>
    <td>
    <asp:RequiredFieldValidator ID="rfvhouse"
           runat="server"
           ControlToValidate="rblhouse"
           ErrorMessage="Enter your house name">
    </asp:RequiredFieldValidator>
    <br />
    </td>
    </tr>
    <tr>
    <td class="style3">
    Class:</td>
    <td class="style2">
    <asp:TextBox ID="txtclass" runat="server"></asp:TextBox>
    </td>
    <td>
    <asp:RangeValidator ID="rvclass"
           runat="server" ControlToValidate="txtclass"
           ErrorMessage="Enter your class (6 - 12)" MaximumValue="12"
           MinimumValue="6" Type="Integer">
    </asp:RangeValidator>
    </td>
    </tr>
    <tr>
    <td class="style3">
    Email:</td>
    <td class="style2">
    <asp:TextBox ID="txtemail" runat="server" Width="250px">
    </asp:TextBox>
    </td>
    <td>
    <asp:RegularExpressionValidator ID="remail"
          runat="server"
          ControlToValidate="txtemail" ErrorMessage="Enter your email"
    ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*">
    </asp:RegularExpressionValidator>
    </td>
    </tr>
    <tr>
    <td class="style3" align="center" colspan="3">
    <asp:Button ID="btnsubmit" runat="server" onclick="btnsubmit_Click"
    style="text-align: center" Text="Submit" Width="140px" />
    </td>
    </tr>
    </table>
    <asp:ValidationSummary ID="ValidationSummary1"
          runat="server"
          DisplayMode ="BulletList"
          ShowSummary ="true"
          HeaderText="Errors:" />
    </form>

The code behind the submit button:

    protected void btnsubmit_Click(object sender, EventArgs e)
    {
       if (Page.IsValid)
       {
          lblmsg.Text = "Thank You";
       }
       else
       {
          lblmsg.Text = "Fill up all the fields";
       }
    }

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