What Do You Call It When a Text Box Is Empty in VB.NET?

It is important that users fill out text boxes before clicking "Submit."

Empty VB.NET text boxes that require data and have none are called errors. Failing to detect these errors can result in an application that produces erroneous results or even crashes. As a VB.NET Web developer, you have access to built-in validators that can help you check for erroneous text boxes using minimal code.

1. Text Box Controls

   • VB.NET allows developers to create text box controls that have no default values. Simply drag a control onto a form, and it's ready to use. Unlike grids, which display data, text boxes usually accept input from users. A user can type data into the text box, or your VB.NET application can place data there in response to a user's action. An empty text box error can result when neither of those events occurs and your code expects a value in the text box.

   Form Validation

   • Writing error validation code from scratch can be time-consuming, especially if you have many VB.NET controls to validate. If you have 10 text boxes, for instance, you must write client-side JavaScript code or server-side ASP.NET code to validate them. Microsoft includes a custom set of validation controls with the .NET framework. The RequiredFieldValidator control, found in the ToolBox window, simplifies the task of checking for empty controls, such as text boxes. An empty control is one that has no data when a user updates a form.

   Validation Controls

   • Adding a RequiredFieldValidator control to a VB.NET form is as simple as dragging the control onto the form from the Toolbox window. After you do that, your code will look similar to this:

     <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server"
     ErrorMessage="Place Message Text Here">
     </asp:RequiredFieldValidator>

     The ErrorMessage attribute contains the text users will see if they forget to add text to a text box. You can change its value to display any message, such as "Please enter a value in this text box."

   Text Box Validation

   • If you want to use the RequiredFieldValidator control to check for an empty text box whose ID is "TextBox1," you can add the following ControlToValidate statement anywhere in your VB.NET code:

     RequiredFieldValidator1.ControlToValidate = TextBox1.ID

     Whenever a user clicks a button or performs any action that triggers a postback to the Web server, the validator will check for an empty text box. If the text box contains no data, your error message text appears. Your form's Load method is a good place to insert the ControlToValidate statement.