VB - TextChanged not triggering properly after the backspace key is hit? - vb.net

Question

My problem boils down to this:
I have six TextBoxes which expect a value that is between 0 and a given number.
What I am trying to achieve is:
If the number entered is between 0 and the specified number (as a label), the text will remain black
If the number entered exceeds the specified number, the text will turn red
The problem here is that if the specified number is "10", and the user enters 11, it turns red, as it should, HOWEVER, if they hit the backspace key (the number entered is now 1) the number remains red, which is not the intended functionality - the number 1 should be black since it's between 0 and the specified number.
All of the specified numbers are hard-coded for now (I'm in a beginner course and this is just something I'm doing for fun to increase the functionality of the program and I haven't gotten to adding classes for each "Assignment" yet) and you can technically input negative numbers, I don't care about that at the moment.
This is the Subroutine which gets added as the handler for all of the textboxes within a certain GroupBox
' Handler which gets added to all TextBoxes in "grpGrades" GroupBox
Private Sub txtGradePoints_TextChanged(sender As Object, e As EventArgs)
' Take in generic sender (Textbox) and convert to TextBox (necessary due to Strict mode)
Dim textBox = CType(sender, TextBox)
Try
' the value of the current TextBox being checked
Dim val = Decimal.Parse(textBox.Text)
Select Case textBox.Name
Case "txtPostPoints"
If val > 10 Then textBox.ForeColor = Color.Red
Case "txtCh1TestPoints", "txtCh2TestPoints", "txtCh3TestPoints"
If val > 50 Then textBox.ForeColor = Color.Red
Case "txtCh2TutPoints", "txtCh3TutPoints"
If val > 25 Then textBox.ForeColor = Color.Red
Case Else
textBox.ForeColor = Color.Black
End Select
Catch
textBox.ForeColor = SystemColors.ControlText
End Try
End Sub
This is the onLoad Handler which gets the appropriate TextBox controls from the "grpGrades" GroupBox and adds the aforementioned TextChanged handler to each one.
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
' Get array of TextBox Controls from the "grpGrades" GroupBox
Dim textBoxes = grpGrades.Controls.OfType(Of TextBox)()
' Go through the array of TextBoxes and add the TextChanged handler to each TextChanged event
For Each txt In textBoxes
AddHandler txt.TextChanged, AddressOf txtGradePoints_TextChanged
Next
'AddHandler txtPostPoints.TextChanged, AddressOf txtGradePoints_TextChanged
'AddHandler txtCh1TestPoints.TextChanged, AddressOf txtGradePoints_TextChanged
'AddHandler txtCh2TestPoints.TextChanged, AddressOf txtGradePoints_TextChanged
'AddHandler txtCh3TestPoints.TextChanged, AddressOf txtGradePoints_TextChanged
'AddHandler txtCh2TutPoints.TextChanged, AddressOf txtGradePoints_TextChanged
'AddHandler txtCh3TutPoints.TextChanged, AddressOf txtGradePoints_TextChanged
End Sub
The last part of the Subroutine is just the commented out code and is how I originally had the Handlers added, just in case something went wrong with my new method.
EDIT: Was it seriously necessary to downvote? For what reason?

Answer 1

Your code never test for a valid value. The Case Else that sets the current textbox to Black is never hit when the current textbox returns to a valid value. This cannot happen because the Select Case will match the current Name of the textbox, will test again for the invalid value and then exits the Select Case block. You need to set the color for the valid value in the appropriate Case for the current text box name. The IF conditional operator could reduce everything to a single line
Private Sub txtGradePoints_TextChanged(sender As Object, e As EventArgs)
' Take in generic sender (Textbox) and convert to TextBox (necessary due to Strict mode)
Dim textBox = CType(sender, TextBox)
Try
' the value of the current TextBox being checked
Dim val = Decimal.Parse(textBox.Text)
Select Case textBox.Name
Case "txtPostPoints"
textBox.ForeColor = IF(val > 10, Color.Red, Color.Black)
Case "txtCh1TestPoints", "txtCh2TestPoints", "txtCh3TestPoints"
textBox.ForeColor = IF(val > 50, Color.Red, Color.Black)
Case "txtCh2TutPoints", "txtCh3TutPoints"
textBox.ForeColor = IF(val > 25, Color.Red, Color.Black)
Case Else
' Not sure if it is needed for other textboxes....
textBox.ForeColor = Color.Black
End Select
Catch
textBox.ForeColor = SystemColors.ControlText
End Try
End Sub

Answer 2

So, as others have said, you're not handling both sides of the If for each text box. You're setting the colour if it meets the condition, but not reversing it.
Here's my way of handling this. It's a bit different, but it keeps all of your code together and doesn't require any of that Case code to work out the name of the calling text box.
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim check As Func(Of TextBox, Decimal, Boolean) =
Function(tb, d)
Dim value As Decimal
If (Decimal.TryParse(tb.Text, value)) Then
Return value > d
End If
Return False
End Function
Dim add As Action(Of TextBox, Decimal) =
Sub(tb, d)
AddHandler tb.TextChanged,
Sub(s, e2)
tb.ForeColor = If(check(tb, d), Color.Red, Color.Black)
End Sub
End Sub
add(txtPostPoints, 10)
add(txtCh1TestPoints, 50)
add(txtCh2TestPoints, 50)
add(txtCh3TestPoints, 50)
add(txtCh2TutPoints, 25)
add(txtCh3TutPoints, 25)
End Sub
So, check is a Func(Of TextBox, Decimal, Boolean) that takes a TextBox and safely parses its text to see if it is greater than the Decimal value and returns True if it is and False otherwise.
And add is an Action(Of TextBox, Decimal) that takes a TextBox and the Decimal and adds the handler to call check set the colour to red or black based on the result of check.
It then is very simple to call add for each TextBox.
All hard-coded with no magic string checks and all nicely encapsulated in the form load method.

Answer 3

You are using the select case based on the name and the only condition is that if it's > 10 then turn the forecolor red. But you're never turning it back. Now before you bring up the case else, let me inform you that the case else would only be based upon the textbox.name and since the name is found case else doesn't come in to play here.
so when a name is found you check the value > 10 and set red but you don't tell it what to do if it isn't > 10