Vlad Setchin: VB.NET - Validating InputBox Control

Friday, 31 March 2017

VB.NET - Validating InputBox Control

If you are working with the system that still uses InputBox control from MS VisualBasic then you may get a situation where the input needs to be validated. InputBox control does not allow any validation checks and in ideal case needs to be replaced with custom WinForms dialog box. This post will show a simple way of validating InputBox by creating InputBoxValidated function and using IStringValidator interface.

	Public Class InputBoxValidated
	Public Function InputBoxValidated _
	(
	prompt As String,
	title As String,
	Optional stringValidator As IStringValidator = Nothing,
	Optional validationMessage As String = ""
	) As String
	Dim value As String _
	= Microsoft.VisualBasic.Interaction.InputBox(prompt, title)

	' If the cancel button wasn't pressed
	' And IStringValidator is passed with validation message
	If Not value = String.Empty AndAlso stringValidator IsNot Nothing _
	AndAlso Not String.IsNullOrEmpty(validationMessage) Then
	If Not stringValidator.Validate(value) Then
	MessageBox.Show(validationMessage, Application.ProductName)
	value = InputBoxValidated(
	prompt, title, stringValidator, validationMessage)
	End If
	End If

	Return value
	End Function
	End Class

view raw vbnet_InputBoxValidated.vb hosted with ❤ by GitHub

As you can see InputBoxValidated function uses IStringValidator interface that can implement any kind of string validations and criteria.

	Public Interface IStringValidator
	Function Validate(value As String) As Boolean
	End Interface

view raw vbnet_IStringValidator.vb hosted with ❤ by GitHub

Below is an example of StringValidator class that implements IStringValidator interface and makes use of StringValidator from System.Configuration.

	Public Class StringValidator
	Implements IStringValidator

	Public Sub New(maxLength As Integer, invalidCharacters As String)
	Me.MaxLength = maxLength
	Me.InvalidCharacters = invalidCharacters
	End Sub

	Public Property MaxLength As Integer
	Public Property InvalidCharacters As String
	Public Function Validate(value As String) _
	As Boolean Implements IStringValidator.Validate
	Dim valid As Boolean = True

	Try
	Dim stringValidator As _
	New System.Configuration.StringValidator _
	(0, MaxLength, InvalidCharacters)
	If stringValidator.CanValidate(value.GetType()) Then
	stringValidator.Validate(value)
	Else
	valid = False
	End If
	Catch ex As ArgumentException
	valid = False
	End Try

	Return valid
	End Function
	End Class