Backgroundworker gives multiple error messages - vb.net

Question

I have a form with three textboxes in it. In my BackgroundWorker1_DoWork handler I test if any TextBox is empty and launch a MessageBox asking the user to fill in all the TextBoxes. This is done in a Try/Catch block. My problem is two fold. If the TextBoxes aren't filled in the user gets the first MessageBox and then another MessageBox when the Catch exception is thrown...so this would be the second MessageBox the user gets. In my BackGroundWorker1_RunWorkCompleted handler I test if an Exception is thrown. It never acknowledges the error and immediately executes the Else block which will be the third message box the user receives saying "Process complete." The Process Complete should not have been shown.
How do I test if there are any TextBoxes not filled in and if they're not throw 1 MessageBox telling the user to fill in all the TextBoxes? And make my RunWorkerComplete handler acknowledge the ElseIf e.Error IsNot Nothing.
Thank you for your help.
Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
BackgroundWorker1.WorkerReportsProgress = True
Try
For Each cntrl As Control In Me.Controls()
If TypeOf cntrl Is TextBox Then
If CType(cntrl, TextBox).Text.Equals(String.Empty) Or (CType(cntrl, TextBox).Text = "") Then
cntrl.BackColor = Color.Yellow
MessageBox.Show("Please enter value in all fields on form" & cntrl.Name.ToString())
cntrl.Focus()
End If
End If
Next
runProgram()
Catch ex As Exception
MessageBox.Show("An error occured while trying to load this application. Please contact Maxine Hammett for assistance " &
vbNewLine & "" & vbNewLine & String.Format("Error: {0}", ex.Message))
End Try
End Sub
Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
If e.Cancelled = True Then
MsgBox(" Operation Cancelled ")
ProgressBar1.Value = 0
ElseIf e.Error IsNot Nothing Then
MsgBox("Error in RunWorkerComplete" & e.Error.Message)
Else
MsgBox(" Process Complete ")
Close()
End If
End Sub
Moved the control checking to the execute button. But now I get errors about the text boxes not having a path (one of the text boxes is a path to folder).
Private Sub btnExecute_Click(sender As Object, e As EventArgs) Handles btnExecute.Click
Dim launchProgram As Boolean = False
While launchProgram = False
For Each cntrl As Control In Me.Controls()
If TypeOf cntrl Is TextBox Then
If CType(cntrl, TextBox).Text.Equals(String.Empty) Or (CType(cntrl, TextBox).Text = "") Then
cntrl.BackColor = Color.Yellow
MessageBox.Show("Please enter value in all fields on form" & cntrl.Name.ToString())
cntrl.Focus()
launchProgram = False
Else
launchProgram = True
End If
End If
Next
End While
If launchProgram = True Then
BackgroundWorker1.RunWorkerAsync()
End If
End Sub

Answer 1

I suggest that you check a single text box a time and show the message if its empty:
Private Sub btnExecute_Click(sender As Object, e As EventArgs) Handles btnExecute.Click
For Each cntrl As TextBox In Controls.OfType(Of TextBox)
If String.IsNullOrEmpty(cntrl.Text) Then
cntrl.BackColor = Color.Yellow
MessageBox.Show("Please enter value in all fields on form" & cntrl.Name.ToString())
cntrl.Focus()
Return
Else
cntrl.BackColor = SystemColors.Window
End If
Next
BackgroundWorker1.RunWorkerAsync()
End Sub
Or maybe concatenate the names of the empty text boxes in the For..Each block if you really need to prompt the user this way:
Private Sub btnExecute_Click(sender As Object, e As EventArgs) Handles btnExecute.Click
Dim sb As New StringBuilder
For Each cntrl As TextBox In Controls.OfType(Of TextBox)
If String.IsNullOrEmpty(cntrl.Text) Then
If sb.Length > 0 Then sb.Append(", ")
sb.Append(cntrl.Name)
cntrl.BackColor = Color.Yellow
Else
cntrl.BackColor = SystemColors.Window
End If
Next
If sb.Length > 0 Then
MessageBox.Show("Please enter value in all fields on form" & sb.ToString())
Controls.OfType(Of TextBox).Where(Function(a) String.IsNullOrEmpty(a.Text)).FirstOrDefault?.Focus()
Return
End If
BackgroundWorker1.RunWorkerAsync()
End Sub
Otherwise, run the worker.
Good luck.