Inheritance and Windows Forms - Validating Inputs

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So far we managed to have 2 forms, with the same basic controls and functionality, much like the “Employee” class and the other inherited classes “Manager” and “Technician”. It shouldn’t stop here, should it?

Uhm, no.

As a matter of fact, if I am adding a Manager, or a Technician, then I want to validate the inputs. We will not, however, make the validation on each form alone (remember the “ManageEmployee” Form). We will put the validation code and make use of the error provider on the “ManageEmployee” form.

We will add a function “IsValidInputs” which will validate the user inputs in the text boxes. It will also set the set the properties of the error provider if any errors were found.


Protected Function IsValidInputs() As Boolean
        Dim strEmployeeName As String
        Dim strEmployeeAge As String 
'Age should be integer, but not we will be reading from the' 
'text box, and we need to validate that it is an integer'
        Dim bIsValidInputs As Boolean = True 
'we start with the assumption that the inputs are valid'
        Try
            strEmployeeName = txtName.Text.Trim
            strEmployeeAge = txtAge.Text.Trim
            'check if the Name is empty'
            If strEmployeeName = String.Empty Then
                bIsValidInputs = False
                errProvider.SetError(txtName, "Please add a Name.")
            Else
                'Make sure to clear the Error Provider
                errProvider.SetError(txtName, "")
            End If
            If strEmployeeAge = String.Empty Then
                bIsValidInputs = False
                errProvider.SetError(txtAge, "Please add an Age.")
            Else
                'Make sure to clear the Error Provider'
                errProvider.SetError(txtAge, "")
            End If
            If Not IsNumeric(strEmployeeAge) Then
                bIsValidInputs = False
                errProvider.SetError(txtAge, "Age should be a number.")
            Else
                'Make sure to clear the Error Provider'
                errProvider.SetError(txtAge, "")
            End If
            Return bIsValidInputs
        Catch oException As Exception
            'Handle any unexpected errors here'
        End Try
    End Function



Let’s get back to the object oriented. The function above should be only visible to the form and the forms inheriting from it. (Yes, it should be protected.)

Next: Carrying Out the Scenario >>
 

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