Validating User Input in VB.NET: Code Example

Posted on Jan 30, 2025 in Computers

VB.NET Code for Input Validation

This code snippet demonstrates a private function in VB.NET designed to validate user input based on different types. The function, named validate, accepts a string parameter type and returns a boolean value indicating whether the validation was successful.

Function Structure

The function initializes two variables:

  • Msg: A string variable to store error messages.
  • valid: A boolean variable initialized to True, representing the validation status.

The initial error message is set to:

Msg = "Entry Errors" & vbCrLf & "****************"

Validation Logic

A Select Case statement is used to determine the type of validation to perform based on the type parameter.

Case “LOGIN”

This section validates input fields typically found in a login form:

  • Rut: Checks if txtRut_I.Text is empty. If so, adds “You must enter the Rut” to Msg and sets valid to False.

  • Check Digit: Checks if txtDv_I.Text is not empty. If it is not empty, it validates whether the entered value is a digit from 0 to 9 or “K” (case-insensitive). If not, it adds “Please enter a valid check digit” to Msg and sets valid to False. If txtDv_I.Text is empty, it adds “You must enter the check digit” to Msg and sets valid to False.

  • Name: Checks if txtNombre_I.Text is empty. If so, adds “Enter the name” to Msg and sets valid to False.

  • Salary: Checks if txtSueldo_I.Text is empty. If so, adds “Enter the salary must Player” to Msg and sets valid to False. If not empty, it further checks if the salary is within the range of $50,000 to $2,000,000. If it is outside this range, it adds “You must enter the value between $50,000 and $2,000,000” to Msg and sets valid to False.

  • Seat: Checks if cbbPuesto_I.SelectedIndex is less than or equal to 0. If so, adds “You must select the Seat” to Msg and sets valid to False.

Case “Modify”

This section validates input fields typically used for modifying existing data. The validation logic is similar to the “LOGIN” case, but it uses different field names (txtRut_M, txtDv_M, txtNombre_M, txtSueldo_M, cbbPuesto_M).

Case “BUSCAR1”

  • Initial Value: Checks if txtValorIni.Text is empty. If so, adds “You must enter the initial value” to Msg and sets valid to False.

  • Final Value: Checks if txtValorFin.Text is empty. If so, adds “Enter the Final Value Must” to Msg and sets valid to False.

Case “BUSCAR2”

  • Seat: Checks if cbbPuesto_C.SelectedIndex is less than or equal to 0. If so, adds “You must select the Seat” to Msg and sets valid to False.

Result

After the Select Case statement, the function checks the value of valid. If valid is False, it means that at least one validation failed. In this case, it displays a message box with the accumulated error messages (Msg) and a title of “WARNING”.

Finally, the function returns True if valid is False, and False otherwise.