Code order

Question

I have a form with textboxes, labels, comboboxes, etc. I have had a problem for quite some time with opening the form to display and the Comboboxes do not display the correct item. It took some time but I found that the order of two lines of code were the problem the entire time. At this point I know what is wrong, but I am unable to understand why it is wrong. SetState("View") BindControls() SetState() is a sub that sets all of the controls on the form, based on the parameters and goes something like this: Private Sub SetState(ByVal AppState As String) #Region "General Form Properties" Me.Text = "Document Record" #End Region Select Case AppState Case "Add" #Region "Button Properties" btnObsolete.Enabled = False btnEdit.Enabled = False btnCancel.Enabled = True btnSave.Enabled = True btnScan.Enabled = False btnItem.Enabled = False btnClose.Enabled = False btnHelp.Enabled = True #End Region #Region "Control Properties" pnlDocRecord.Enabled = True lblDocID.Visible = True txtName.ReadOnly = False txtDescription.ReadOnly = False lblFilePath.ForeColor = Color.Blue cboDoc.Enabled = False cboDoc.TabIndex = 2 cboDoc.TabStop = False cboDoc.ValueMember = "DocType" cboDoc.DisplayMember = "DocType" cboDoc.SelectedIndex = -1 cboOwner.Enabled = False cboOwner.TabIndex = 2 cboOwner.TabStop = False cboOwner.ValueMember = "Department" cboOwner.DisplayMember = "Department" cboOwner.SelectedIndex = -1 cboWhere.Enabled = False cboWhere.TabIndex = 2 cboWhere.TabStop = False cboWhere.ValueMember = "Where" cboWhere.DisplayMember = "Where" cboWhere.SelectedIndex = -1 rdoActive.Visible = True rdoActive.Enabled = False rdoObsolete.Visible = True rdoObsolete.Enabled = False txtName.Focus() #End Region Case "Edit", "Revise" #Region "Button Properties" btnObsolete.Enabled = False btnEdit.Enabled = False btnCancel.Enabled = True btnSave.Enabled = True btnScan.Enabled = False btnItem.Enabled = False btnClose.Enabled = False btnHelp.Enabled = True #End Region #Region "Control Properties" pnlDocRecord.Enabled = True lblDocID.Visible = True txtName.ReadOnly = False txtName.TabIndex = 0 txtName.TabStop = True txtDescription.ReadOnly = False txtDescription.TabIndex = 1 txtDescription.TabStop = True lblFilePath.ForeColor = Color.Blue cboDoc.Enabled = True cboDoc.TabIndex = 2 cboDoc.TabStop = True cboDoc.DataSource = DocBindingSource cboDoc.ValueMember = "DocType" cboDoc.DisplayMember = "DocType" cboOwner.Enabled = True cboOwner.TabIndex = 3 cboOwner.TabStop = True cboOwner.DataSource = OwnerBindingSource cboOwner.ValueMember = "Department" cboOwner.DisplayMember = "Department" cboWhere.Enabled = True cboWhere.TabIndex = 4 cboWhere.TabStop = True cboWhere.DataSource = WhereBindingSource cboWhere.ValueMember = "Where" cboWhere.DisplayMember = "Where" rdoActive.Visible = True rdoActive.Enabled = False rdoObsolete.Visible = True rdoObsolete.Enabled = False txtName.Focus() #End Region Case "View" #Region "Button Properties" btnObsolete.Enabled = False If MyUser = "DocMaster" Then btnEdit.Enabled = False Else btnEdit.Enabled = True btnCancel.Enabled = False btnSave.Enabled = False btnScan.Enabled = False btnItem.Enabled = False btnClose.Enabled = True btnHelp.Enabled = True #End Region #Region "Control Properties" pnlDocRecord.Enabled = True lblDocID.Visible = True txtName.ReadOnly = True txtName.TabIndex = 0 txtName.TabStop = False txtDescription.ReadOnly = True txtDescription.TabIndex = 1 txtDescription.TabStop = False lblFilePath.ForeColor = Color.Blue cboDoc.Enabled = False cboDoc.TabIndex = 2 cboDoc.TabStop = False cboDoc.DataSource = DocBindingSource cboDoc.ValueMember = "DocType" cboDoc.DisplayMember = "DocType" cboDoc.SelectedIndex = -1 cboOwner.Enabled = False cboOwner.TabIndex = 3 cboOwner.TabStop = False cboOwner.DataSource = OwnerBindingSource cboOwner.ValueMember = "Department" cboOwner.DisplayMember = "Department" cboOwner.SelectedIndex = -1 cboWhere.Enabled = False cboWhere.TabIndex = 4 cboWhere.TabStop = False cboWhere.DataSource = WhereBindingSource cboWhere.ValueMember = "Where" cboWhere.DisplayMember = "Where" cboWhere.SelectedIndex = -1 rdoActive.Visible = True rdoActive.Enabled = False rdoObsolete.Visible = True rdoObsolete.Enabled = False txtName.Focus() #End Region End Select End Sub BindControls() does exactly as named. It is to bind the controls with table values. Private Sub BindControls() Dim MasterBaseBindingSource As New BindingSource MasterBaseBindingSource.DataSource = MasterBase lblDocID.DataBindings.Add("Text", MasterBase.ListTable, "MasterBaseID") lblRev.DataBindings.Add("Text", MasterBase.ListTable, "Revision") txtName.DataBindings.Add("Text", MasterBase.ListTable, "Title") txtDescription.DataBindings.Add("Text", MasterBase.ListTable, "Description") lblFilePath.DataBindings.Add("Text", MasterBase.ListTable, "FilePath") cboDoc.DataBindings.Add("Text", MasterBase.ListTable, "DocType") cboWhere.DataBindings.Add("Text", MasterBase.ListTable, "WhereUsed") cboOwner.DataBindings.Add("Text", MasterBase.ListTable, "Owner") rdoActive.DataBindings.Add("Checked", MasterBase.ListTable, "Effective", True, DataSourceUpdateMode.OnValidation, CheckState.Indeterminate) rdoObsolete.DataBindings.Add("Checked", MasterBase.ListTable, "Obsolete", True, DataSourceUpdateMode.OnValidation, CheckState.Indeterminate) End Sub I am having no problem with either of the methods/subs. However, after hours and hours and hours of watching this crap run, I found that the problem is related to the order of the two lines of code (above) is reversed. I have noticed that if the order is changed, all of the table data on the form is displayed correctly, except the data for the comboboxes. Which is what blows my mind. Why is it that only the combobox data is sensitive to the order of the two lines? Whooosh!!! There it went again. Over my head!

Answer 1

Hi GlennWalker-1236,
First, you need to note that ComboBox does not provide SelectedItemChanged event which is required for correctly binding to SelectedItem.
Only the SelectedValue property of the ComboBox, CheckedListBox, and ListBox control is simple bound.
More details you can refer this document.
For combobox binding data, you need to set the two Member properties(ValueMember,DisplayMember )of ComboBox and load your dataSource:

comboBox.DataSource = dataSource;  
comboBox.ValueMember = valueMember;  
comboBox.DisplayMember = displayMember;  

Otherwise it will prevent the correct rebinding of the DataSource.
Then bind the selected value to your column.

comboBox.DataBindings.Add("SelectedValue", boundDataSource, boundDataMember);  

You can also try to reset the DataSource of the ComboBox(set it to null) and rebind it.
So you need to call the SetState("View") method then BindControls().
Here is a related thread and hope helpful for you.
Best Regards,
Daniel Zhang

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Answer 2

Actually I did that. Finger pinky swear. It just came out the way it did. Your interface sometimes leaves much to be desired.

Anyway, here I go again and it looks better.

Form Event:

Private Sub DocRecord_Shown(sender As Object, e As EventArgs) Handles MyBase.Shown
        If MyUser = "DocMaster" Then
            GetDocument(MasterID)
            SetState("View")
            BindControls()
        Else
            Select Case DocState
                Case "Add"
                    UpRevision = ""
                    MasterID = GetMasterBaseID(MasterID).ToString 'Create MasterBase ID
                    lblDocID.Text = MasterID
                    lblFilePath.Text = GetDirectory(MyDirectory).ToString
                    lblRev.Text = IncrementAARevision(UpRevision).ToString
                    rdoActive.Checked = False
                    SetState("View")
                Case "View", "Edit", "Revise"
                    GetDocument(MasterID)
                    If DocState = "Revise" Then
                        SetState("Edit")
                        BindControls()
                        UpRevision = lblRev.Text
                        lblDocID.Text = MasterID
                        lblRev.Text = IncrementAARevision(UpRevision).ToString()
                        lblFilePath.Text = GetDirectory(MyDirectory).ToString
                        rdoActive.Checked = False
                        cboDoc.Text = ""
                        cboOwner.Text = ""
                        cboWhere.Text = ""
                    Else
                        SetState("View")
                        BindControls()
                    End If
            End Select
        End If
    End Sub

So, basically, the two lines:

            SetState("View")
            BindControls()

must be in this order, else any combo box on the form will not execute correctly.

Set State:

    Private Sub SetState(ByVal AppState As String)
#Region "General Form Properties"
        Me.Text = "Document Record"
#End Region
        Select Case AppState
            Case "Add"
#Region "Button Properties"
                btnObsolete.Enabled = False
                btnEdit.Enabled = False
                btnCancel.Enabled = True
                btnSave.Enabled = True
                btnScan.Enabled = False
                btnItem.Enabled = False
                btnClose.Enabled = False
                btnHelp.Enabled = True
#End Region
#Region "Control Properties"
                pnlDocRecord.Enabled = True
                lblDocID.Visible = True
                txtName.ReadOnly = False
                txtDescription.ReadOnly = False
                lblFilePath.ForeColor = Color.Blue
                cboDoc.Enabled = False
                cboDoc.TabIndex = 2
                cboDoc.TabStop = False
                cboDoc.ValueMember = "DocType"
                cboDoc.DisplayMember = "DocType"
                cboDoc.SelectedIndex = -1
                cboOwner.Enabled = False
                cboOwner.TabIndex = 2
                cboOwner.TabStop = False
                cboOwner.ValueMember = "Department"
                cboOwner.DisplayMember = "Department"
                cboOwner.SelectedIndex = -1
                cboWhere.Enabled = False
                cboWhere.TabIndex = 2
                cboWhere.TabStop = False
                cboWhere.ValueMember = "Where"
                cboWhere.DisplayMember = "Where"
                cboWhere.SelectedIndex = -1
                rdoActive.Visible = True
                rdoActive.Enabled = False
                rdoObsolete.Visible = True
                rdoObsolete.Enabled = False

                txtName.Focus()
#End Region
            Case "Edit", "Revise"
#Region "Button Properties"
                btnObsolete.Enabled = False
                btnEdit.Enabled = False
                btnCancel.Enabled = True
                btnSave.Enabled = True
                btnScan.Enabled = False
                btnItem.Enabled = False
                btnClose.Enabled = False
                btnHelp.Enabled = True
#End Region
#Region "Control Properties"
                pnlDocRecord.Enabled = True
                lblDocID.Visible = True
                txtName.ReadOnly = False
                txtName.TabIndex = 0
                txtName.TabStop = True
                txtDescription.ReadOnly = False
                txtDescription.TabIndex = 1
                txtDescription.TabStop = True
                lblFilePath.ForeColor = Color.Blue
                cboDoc.Enabled = True
                cboDoc.TabIndex = 2
                cboDoc.TabStop = True
                cboDoc.DataSource = DocBindingSource
                cboDoc.ValueMember = "DocType"
                cboDoc.DisplayMember = "DocType"
                cboOwner.Enabled = True
                cboOwner.TabIndex = 3
                cboOwner.TabStop = True
                cboOwner.DataSource = OwnerBindingSource
                cboOwner.ValueMember = "Department"
                cboOwner.DisplayMember = "Department"
                cboWhere.Enabled = True
                cboWhere.TabIndex = 4
                cboWhere.TabStop = True
                cboWhere.DataSource = WhereBindingSource
                cboWhere.ValueMember = "Where"
                cboWhere.DisplayMember = "Where"
                rdoActive.Visible = True
                rdoActive.Enabled = False
                rdoObsolete.Visible = True
                rdoObsolete.Enabled = False

                txtName.Focus()
#End Region
            Case "View"
#Region "Button Properties"
                btnObsolete.Enabled = False
                If MyUser = "DocMaster" Then btnEdit.Enabled = False Else btnEdit.Enabled = True
                btnCancel.Enabled = False
                btnSave.Enabled = False
                btnScan.Enabled = False
                btnItem.Enabled = False
                btnClose.Enabled = True
                btnHelp.Enabled = True
#End Region
#Region "Control Properties"
                pnlDocRecord.Enabled = True
                lblDocID.Visible = True
                txtName.ReadOnly = True
                txtName.TabIndex = 0
                txtName.TabStop = False
                txtDescription.ReadOnly = True
                txtDescription.TabIndex = 1
                txtDescription.TabStop = False
                lblFilePath.ForeColor = Color.Blue
                cboDoc.Enabled = False
                cboDoc.TabIndex = 2
                cboDoc.TabStop = False
                cboDoc.DataSource = DocBindingSource
                cboDoc.ValueMember = "DocType"
                cboDoc.DisplayMember = "DocType"
                cboDoc.SelectedIndex = -1
                cboOwner.Enabled = False
                cboOwner.TabIndex = 3
                cboOwner.TabStop = False
                cboOwner.DataSource = OwnerBindingSource
                cboOwner.ValueMember = "Department"
                cboOwner.DisplayMember = "Department"
                cboOwner.SelectedIndex = -1
                cboWhere.Enabled = False
                cboWhere.TabIndex = 4
                cboWhere.TabStop = False
                cboWhere.DataSource = WhereBindingSource
                cboWhere.ValueMember = "Where"
                cboWhere.DisplayMember = "Where"
                cboWhere.SelectedIndex = -1
                rdoActive.Visible = True
                rdoActive.Enabled = False
                rdoObsolete.Visible = True
                rdoObsolete.Enabled = False

                txtName.Focus()
#End Region
        End Select
    End Sub

BindControls():

Private Sub BindControls()
        Dim MasterBaseBindingSource As New BindingSource
        MasterBaseBindingSource.DataSource = MasterBase
        lblDocID.DataBindings.Add("Text", MasterBase.ListTable, "MasterBaseID")
        lblRev.DataBindings.Add("Text", MasterBase.ListTable, "Revision")
        txtName.DataBindings.Add("Text", MasterBase.ListTable, "Title")
        txtDescription.DataBindings.Add("Text", MasterBase.ListTable, "Description")
        lblFilePath.DataBindings.Add("Text", MasterBase.ListTable, "FilePath")
        cboDoc.DataBindings.Add("Text", MasterBase.ListTable, "DocType")
        cboWhere.DataBindings.Add("Text", MasterBase.ListTable, "WhereUsed")
        cboOwner.DataBindings.Add("Text", MasterBase.ListTable, "Owner")
        rdoActive.DataBindings.Add("Checked", MasterBase.ListTable, "Effective", True, DataSourceUpdateMode.OnValidation, CheckState.Indeterminate)
        rdoObsolete.DataBindings.Add("Checked", MasterBase.ListTable, "Obsolete", True, DataSourceUpdateMode.OnValidation, CheckState.Indeterminate)
    End Sub

This order, for those two lines, only matter where comboboxes are concerned. I cannot, for the life of me, understand why this is so.

Answer 3

Thanks, that helps a lot.

Answer 4

Just an FYI about setting the ComboBox's DataSource: always set the DataSource after you set the DisplayMember and ValueMember, not before (otherwise the events will fire twice, once when you set DisplayMember and again when you set ValueMember). The events will only fire once if you set those two before you set the DataSource.

If you're interested, see my blog post: https://geek-goddess-bonnie.blogspot.com/2018/08/combobox-gotcha-2.html

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~~Bonnie DeWitt [MVP since 2003]
[http://geek-goddess-bonnie.blogspot.com]2