In HTML you can perform validation either by checking the values at client-side or after submitting the form at the server-side. But these methods in HTML take lots of time to create and maintain the code. Moreover, if the user has disabled JavaScript then he or she may not receive the message regarding the error.
Therefore, in ASP.NET you can use ASP.NET Validation Controls while creating the form and specify what ASP.NET Validation Controls you want to use and to which server control you want bind this. ASP.NET Validation Controls are derived from a common base class and share a common set of properties and methods. You just have to drag and drop the ASP.NET Validation Control in the web form and write one line of code to describe its functionality.
This reduces the developer time from writing JavaScript for each type of validation. Moreover, through ASP.NET Validation Controls if any invalid data is entered the browser itself detects the error on the client side and displays the error without requesting the server. This is another advantage because it reduces the server load.
The five types of ASP.NET Validation Controls in ASP.NET Framework include:
• RequiredField Validation control: prompts message if any input field is left blank. This validation control can also be used to prompt message to the user if he or she has left any input field with its default value.
• Range Validation control: Prompts message to the user, if the data entered in the input field is not within the range of the values specified by the Maximum and Minimum properties of the validation control.
• Comparison Validation control: Allows the user to compare two values and check for comparisons such as equality, greater-than, less-than etc. In addition you can check whether the data entered in the input field is of the data type as specified by you.
• RegularExpression Validation control: Allows you to validate if the format of a certain input field is correct or not. You can check the validation of the commonly performed formats such as social security numbers, e-mail addresses, telephone numbers, and postal code.
• Custom Validation control: Allows you to define your own condition for validating the data in the input fields. Two validation functions can be performed using Custom Validation control: first on the server-side and second on the client-side. These functions contain logic defined by you to validate the input fields. These functions returns the True value and False value, if the condition you specified is correct or not respectively.
If the control's value does not validate to what you have specified in the validation control tag, the web form displays an error message. Moreover, you can customize the format of the error message by using the control properties such as BackColor, BorderStyle, and BorderWidth. In addition, you can use Cascading Style Sheet (CSS) to format an error message.
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