One Event handler for an array of checkboxes?

Question

I have an array of checkboxes and a form with multiple checkboxes on it. I want a counter that displays (in real time) how many are checked.

Rather than coding a duplicate "_CheckedChanged()" event for every single one, is there a way to have a single _CheckedChanged() even for the entire array?

> Private Sub frmMain_Load(...

>      Dim intChecked as Integer = 0

>      checkboxes = New CheckBox() {cbxTrackDefault, chkThumb01, chkThumb02, chkThumb03, ...

(What I've tried. DOESN'T WORK. Clearly, I don't know what I'm doing.)

> Private Sub CheckboxHandler(ByVal sender As CheckBox, ByVal e As System.EventArgs)

>     Dim position As Integer = 0

>     position = Array.IndexOf(checkboxes, checkboxes)

>     AddHandler checkboxes(position).CheckedChanged, AddressOf CheckboxHandler

>     If sender.Checked = True Then

>         intChecked += 1

>     Else

>         intChecked -= 1

>     End If

>     lblChecked.Text = intChecked

> End Sub

There must be a simple solution. Any assistance appreciated. TIA

Answer 1

Hi
Here is a stand alone example that may help. This is for dynamically adding Buttons but the principle is the same for most/any controls. It can easily be changed to add CheckBoxes if needed - just adjust the Properties being added. See line 26, where the same event handler is allocated to each Button.

' Blank Form1, copy/replace all
' default code with this code
Option Strict On
Option Explicit On
Public Class Form1
  Dim pan As New Panel
  Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Size = New Size(500, 300)
    With pan
      .Location = New Point(5, 5)
      .Size = New Size(ClientSize.Width - 20, 220)
      .BackColor = Color.Beige
      .BorderStyle = BorderStyle.FixedSingle
    End With
    Controls.Add(pan)
    SetButtons(18)
  End Sub
  Sub SetButtons(num As Integer)
    Dim x As Integer = 2
    Dim y As Integer = 5
    Dim yStep As Integer = 30
    Dim cs As Integer = pan.Height
    For i As Integer = 1 To num
      Dim mybutton As New Button With {.Text = "Button" & i.ToString(), .Name = "Button" & i.ToString(), .Location = New Point(x, y), .BackColor = Color.LightGray, .AutoSize = True}
      pan.Controls.Add(mybutton)
      AddHandler mybutton.Click, AddressOf ButtonClick
      y += yStep
      If y + yStep >= cs Then
        x += 100
        y = 5
      End If
    Next
  End Sub
  Public Sub ButtonClick(sender As Object, e As EventArgs)
    Dim butt As Button = DirectCast(sender, Button)
    MessageBox.Show("Selected Button = " & butt.Name)
  End Sub
End Class

Answer 2

I found a nice simple solution (based on some code found here.)

(see: "checkboxes" array defined in original question.)

Right after the array assignment, I added:

>         For intCnt = 0 To UBound(checkboxes)

>             AddHandler checkboxes(intCnt).CheckedChanged, AddressOf _CheckedChanged

>         Next

Then, at the end of my code, I added the following Event Handler:

>     Private Sub _CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)

>         If sender.checked Then

>             For intCnt = 0 To UBound(checkboxes)

>                 If checkboxes(intCnt) Is sender Then

>                     intChecked += 1

>                 End If

>             Next intCnt

>         Else

>             intChecked -= 1

>         End If

>         lblChecked.Text = intChecked

>     End Sub

The "_CheckedChanged" event is now triggered no matter which checkbox is clicked (PROBLEM: checkboxes NOT in the array are triggered too.)

I'll update my answer when I find a fix to ignore checkboxes not in the array.

UPDATE: I found a (simplistic) way of ignoring other checkboxes simply by checking the "sender.Name" property in the "If/Then" (VB won't show it as an option in the popup, but it's valid.)

If sender.checked And InStr(sender.name, "chkThumb") > 0 Then