Workaround for disappearing checks in the CheckedListBox control

• Download source files and executable - 11.3 Kb

Introduction

As many reported on the newsgroups (including me!), the CheckedListBox control forgets which item is checked when the items have been filled using the DataSource property and when its Visible property is set to false, then back to true.  The problem also occurs when it is hosted on a TabControl and tabs are flipped.

I first ran into this issue in my first week of .NET development.  Very frustrating start!  Since then, I tried many workarounds but all were just an extreme pain in the neck, especially when I was trying to use them on more complex forms. 

Those workarounds included never setting the Visible property of the CheckedListBox to False.  Rather, I moved the control outside the form (ex: -5000, -5000).  It worked (most of the time), but some clients reported the problem even with this. 

I also tried saving all the checks in an array before setting Visible to False, then putting them back in the CheckedListBox on Visible=true but once again, I felt it was a quite ineffective way.

Back then, I did not know that this bug was related to the Datasource property.  I recently figured this out after pulling my hair for a couple hours.  I finally came up with a great and easy workaround...

The Workaround

As I mentioned earlier, the problem only occurs when DataSource is used to add the items to the CheckedListBox.  So the idea is, you guessed it, to NOT use DataSource! :)  Here's the code I came up with:

Private Sub SetClBoxDataSource(ByVal clb As CheckedListBox, 
                 ByVal dt As DataTable)

    'Clear it

    clb.Items.Clear()

    'Fill it

    Dim x As Integer
    For x = 0 To dt.DefaultView.Count - 1
        clb.Items.Add(dt.DefaultView.Item(x))
    Next

End Sub

Basically, what this code does is adding the items one by one using a simple loop.  Now, instead of using this code to fill up the CheckedListBox:

    CheckedListBox.DataSource = DataTable

You should do:

    SetClBoxDataSource(CheckedListBox, DataTable)

It couldn't be easier!  Only one line of code to change!