Validation Controls in Asp Net

Today we will discuss Validation Controls in Asp.Net and we will have a deep look on Custom Validator control in Asp.net.

Validation is a most important process either it is a web based application, desktop application or some other like android or iPhone. without proper validation, it is very difficult for a system to survive because we don't know the nature of client/audience so as per our requirements we will must have to check the input from user and then process it.

Asp.Net provides very powerful controls for validation. In Asp.Net we have basically six validation control which can be used as per the requirements. we can validate the useless or contradictory data input from user. if something is going to harm the system we can validate and stop the user request with proper message or user friendly alert.

Asp.Net gives following validation controls:

• RequiredFieldValidator
• RangeValidator
• CompareValidator
• RegularExpressionValidator
• CustomValidator
• ValidationSummary

What is BaseValidator Class: All validation control performs some operation according to their nature and these control have their built-in classes, these control classes are inherited from a base class that's called BaseValidator class, which give some common properties and method to all validation controls. you can check in below image:

Now we will check validation control in details.

1. RequiredFieldValidator Control:

RequiredFieldValidator is generally used with input text field to check whether the input field is empty or have some text and it will validate that input text field should must have some text not empty.

Example/use of RequiredFieldValidator:

<asp:TextBox ID="txtUserName" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="rfvcUserName" runat="server" ControlToValidate ="txtUserName" ErrorMessage="Please enter Username"></asp:RequiredFieldValidator>

In above example, we can check how we will use RequiredFieldValidator with a Asp.Net TextBox.

2. RangeValidator Control:

On mostly website we have seen it asks for password should be minimum 6 and maximum 20 in length. if we enter less than 6 or greater than 20 it will never let us proceed further. RangeValidator control is used to check whether input from the user falls between this range or no.

RangeValidator has three specific properties:

Type: It check the type of input from the user. The available values are: Date, Double, Currency, Integer, and String.

MinimumValue specifies minimum value of the range.

MaximumValue specifies maximum value of the range.

Syntax/Example of RangeValidator control is as:

<asp:TextBox ID="txtPassword" runat="server" TextMode="Password"></asp:TextBox>
        <asp:RangeValidator ID="rvPasswords" runat="server" ControlToValidate="txtPassword" ErrorMessage="Enter your password between 6 - 12 (only number)" MaximumValue="12" MinimumValue="6" Type="Integer"></asp:RangeValidator>

In above example, we create a password textbox field and in RangeValidator we have set the properties like user can only enter length between 6 to 12 because MinimumValue will check that input should not be less than 6 and MaximumValue will verify input should not b greater than 12, we have set Type is Integer so user can only enter Integers otherwise RangeValidtor will not pass the validation.

3. CompareValidator Control:

When we are submitting a registration form to create a user profile then mostly it requires to set Password for your account, always there are two password fields with label Password and Confirm Password. whatever password we set for the account we have to match the Password and Confirm Password fields. how this confirm password verifies the user input is same that could be done in Asp.Net by using CompareValidator control. we can perform this operation by many other ways and also, we can use CompareValidator control for many other purposes but it was most general and used example for this control.

however, let's have a look on some specific properties of this control:

Type: specifies the data type.

ControlToCompare check the value of the input control to compare with.

ValueToCompare verifies constant value to compare with.

Operator it provides comparison operator, the available values are: GreaterThan, GreaterThanEqual, LessThan, Equal, NotEqual, LessThanEqual, and DataTypeCheck.

Syntax/Example of this control is:

<asp:TextBox id="TextBox1" runat="server"/><br />
        <asp:TextBox id="TextBox2" runat="server"/>
        <asp:CompareValidator id="Compare1" ControlToValidate="TextBox1" ControlToCompare="TextBox2" Type="String" Text="Value does not match" runat="server"/>

In above example, we have two Textboxes and we are comparing their values with each other. if user input is different in both textboxes then it will not pass validation and show the error message "Value does not match".

4. RegularExpressionValidator Control:
RegularExpressionValidator is used when we want our input to be verified with a specific pattern,it may be some phone number format,currency.etc,or we want our input should only contain alphabets not numbers.basically we use a regular expression to match the input which can be done by using RegularExpressionValidator control. we set a regular expression in this control and tell the validator control name of input field then it verifies that input field should validate the expression.
Let's have a look on simple example:

<asp:TextBox ID="txtName" runat="server"/>
    <asp:RegularExpressionValidator ID="regexpName" runat="server" ErrorMessage="This expression does not validate." ControlToValidate="txtName" ValidationExpression="^[a-zA-Z']$" />

5. CustomValidator Control:

Sometime we do not require above all control to check our input and we want to perform some other operation on the user input. so, for such purpose we can use customValidator control. we can perform client side operation and server side also by using this customer control validator. for check input at client side we can use ClientValidationFunction property and for server we can use ServerValidate event handler. client routine can be built by using any script language like Javascript or VBScript or any other understand by browser and in server side we can use any Asp.Net language like C# or VB.Net.

Syntax/Example for the control is:

<asp:TextBox id="Text1" runat="server" />
    <asp:CustomValidator id="CustomValidator1" ControlToValidate="Text1" ClientValidationFunction="ClientValidateFunction" OnServerValidate="ServerValidationFunc" ErrorMessage="Not an even number!" runat="server"/>

In above example, we can see we set the client side and server side routines to perform the operation.

6. ValidationSummary Control:

ValidationSummary is basically used to summarize the error messages from all validation control on the page. it shows the error messages per the DisplayMode property. it collects all validation control error message from a common property "ErrorMessage" of each control. if we skip the ErrorMessage property of any validation control then it will not show error message for that control. there are different properties to present error messages nicely on page by using ValidationSummary Control.

Syntax/Example Lets understand with an example:

<asp:TextBox ID="TextBox2" runat="server" />
            <asp:RequiredFieldValidator ID="RequiredFieldValidator1" ControlToValidate="TextBox2" ErrorMessage="Enter Card Type" Text="*" runat="server"/>
            <asp:TextBox ID="TextBox1" runat="server" />
            <asp:RequiredFieldValidator ID="RequiredFieldValidator2" ControlToValidate="TextBox1" ErrorMessage="Enter Card Number" Text="*" runat=server/>
            <asp:ValidationSummary id="valSum" DisplayMode="BulletList" EnableClientScript="true" HeaderText="You must enter a value in the following fields:" runat="server"/>

In above example validationsummary will show error message, in bullets, from the both required field validator control with a header text.

Comments and Suggestions are always welcome