Modal Wait Dialogue with BackgroundWorker

C# version here.

This is something that I've been meaning to do for some time but never got around to previously. Earlier today - and not for the first time - I saw someone trying to display a modal wait dialogue while they did some work and going about it in very much the wrong way.

This demo provides a dialogue that you can display modally over another form while that form does some background work. You basically write a normal DoWork event handler for a BackgroundWorker, as well as optional ProgresssChanged and RunWorkerCompleted event handlers, and pass them to the dialogue for it to use as handlers for the events of its own BackgroundWorker. That means that your form creates and displays the dialogue, the dialogue then kicks off a BackgroundWorker and it invokes methods in your form to do the work. That way, this same dialogue can be used for any work you like without change.

The dialogue displays a Marquee ProgressBar by default and no Cancel button. If you provide a handler for the ProgressChanged event, it will display a Continuous ProgressBar so the actual progress can be displayed. Note that the Maximum of that ProgressBar is 100 so you must provide a genuine percentage when you call ReportProgress. If you set SupportsCancellation to True, the dialogue will also display a Cancel button. As always, it's up to you to process the cancellation request in your DoWork event handler.

I have replaced the original attachment with one that includes a few improvements, as well as a C# version of the project. This version was created in VS 2019 and targets .NET Framework 4.8. If you're using an earlier version, you should still just be able to add the forms as existing items to a project of your own, as long as you're not using too-old a version.

See post #9 for simple instructions on how to add this dialogue form to your existing project.

For those who would like to see the code without having to download the solution, here you go:

vb.net Code:

Imports System.ComponentModel
 
Public Class BackgroundWorkerForm
 
#Region "Constructors"
 
    ''' <summary>
    ''' Creates a new instance of the <see cref="BackgroundWorkerForm"/> class.
    ''' </summary>
    ''' <remarks>
    ''' Parameterless constructor is private to ensure handlers are provided for <see cref="BackgroundWorker"/>.
    ''' </remarks>
    Private Sub New()
        ' This call is required by the designer.
        InitializeComponent()
    End Sub
 
    ''' <summary>
    ''' Creates a new instance of the <see cref="BackgroundWorkerForm" /> class.
    ''' </summary>
    ''' <param name="onDoWork">
    ''' Handler for the <see cref="BackgroundWorker.DoWork">RunWorkerCompleted</see> event of a <see cref="BackgroundWorker"/>.
    ''' </param>
    Public Sub New(onDoWork As DoWorkEventHandler)
        Me.New()
 
        'Remote event handlers
        AddHandler BackgroundWorker1.DoWork, onDoWork
 
        'Local event handlers
        AddHandler BackgroundWorker1.RunWorkerCompleted, AddressOf BackgroundWorker1_RunWorkerCompleted
    End Sub
 
    ''' <summary>
    ''' Creates a new instance of the <see cref="BackgroundWorkerForm" /> class.
    ''' </summary>
    ''' <param name="onDoWork">
    ''' Handler for the <see cref="BackgroundWorker.DoWork">RunWorkerCompleted</see> event of a <see cref="BackgroundWorker"/>.
    ''' </param>
    ''' <param name="onProgressChanged">
    ''' Handler for the <see cref="BackgroundWorker.ProgressChanged">RunWorkerCompleted</see> event of a <see cref="BackgroundWorker"/>.
    ''' </param>
    Public Sub New(onDoWork As DoWorkEventHandler,
                   onProgressChanged As ProgressChangedEventHandler)
        Me.New()
 
        'Remote event handlers
        AddHandler BackgroundWorker1.DoWork, onDoWork
        AddHandler BackgroundWorker1.ProgressChanged, onProgressChanged
 
        'Local event handlers
        AddHandler BackgroundWorker1.ProgressChanged, AddressOf BackgroundWorker1_ProgressChanged
        AddHandler BackgroundWorker1.RunWorkerCompleted, AddressOf BackgroundWorker1_RunWorkerCompleted
 
        'A ProgressChanged handler has been provided so the ProgressBar will be updated explicitly based on the BackgroundWorker.
        BackgroundWorker1.WorkerReportsProgress = True
        ProgressBar1.Style = ProgressBarStyle.Continuous
    End Sub
 
    ''' <summary>
    ''' Creates a new instance of the <see cref="BackgroundWorkerForm" /> class.
    ''' </summary>
    ''' <param name="onDoWork">
    ''' Handler for the <see cref="BackgroundWorker.DoWork">RunWorkerCompleted</see> event of a <see cref="BackgroundWorker"/>.
    ''' </param>
    ''' <param name="onRunWorkerCompleted">
    ''' Handler for the <see cref="BackgroundWorker.RunWorkerCompleted">RunWorkerCompleted</see> event of a <see cref="BackgroundWorker"/>.
    ''' </param>
    Public Sub New(onDoWork As DoWorkEventHandler,
                   onRunWorkerCompleted As RunWorkerCompletedEventHandler)
        Me.New()
 
        'Remote event handlers
        AddHandler BackgroundWorker1.DoWork, onDoWork
        AddHandler BackgroundWorker1.RunWorkerCompleted, onRunWorkerCompleted
 
        'Local event handlers
        AddHandler BackgroundWorker1.RunWorkerCompleted, AddressOf BackgroundWorker1_RunWorkerCompleted
    End Sub
 
    ''' <summary>
    ''' Creates a new instance of the <see cref="BackgroundWorkerForm" /> class.
    ''' </summary>
    ''' <param name="onDoWork">
    ''' Handler for the <see cref="BackgroundWorker.DoWork">RunWorkerCompleted</see> event of a <see cref="BackgroundWorker"/>.
    ''' </param>
    ''' <param name="onProgressChanged">
    ''' Handler for the <see cref="BackgroundWorker.ProgressChanged">RunWorkerCompleted</see> event of a <see cref="BackgroundWorker"/>.
    ''' </param>
    ''' <param name="onRunWorkerCompleted">
    ''' Handler for the <see cref="BackgroundWorker.RunWorkerCompleted">RunWorkerCompleted</see> event of a <see cref="BackgroundWorker"/>.
    ''' </param>
    Public Sub New(onDoWork As DoWorkEventHandler,
                   onProgressChanged As ProgressChangedEventHandler,
                   onRunWorkerCompleted As RunWorkerCompletedEventHandler)
        Me.New()
 
        'Remote event handlers
        AddHandler BackgroundWorker1.DoWork, onDoWork
        AddHandler BackgroundWorker1.ProgressChanged, onProgressChanged
        AddHandler BackgroundWorker1.RunWorkerCompleted, onRunWorkerCompleted
 
        'Local event handlers
        AddHandler BackgroundWorker1.ProgressChanged, AddressOf BackgroundWorker1_ProgressChanged
        AddHandler BackgroundWorker1.RunWorkerCompleted, AddressOf BackgroundWorker1_RunWorkerCompleted
 
        'A ProgressChanged handler has been provided so the ProgressBar will be updated explicitly based on the BackgroundWorker.
        BackgroundWorker1.WorkerReportsProgress = True
        ProgressBar1.Style = ProgressBarStyle.Continuous
    End Sub
 
#End Region 'Constructors
 
#Region "Properties"
 
    Public WriteOnly Property SupportsCancellation As Boolean
        Set
            BackgroundWorker1.WorkerSupportsCancellation = Value
 
            'If the worker can be cancelled, show the Cancel button and make the form big enough to see it.
            cancelWorkButton.Visible = Value
            Height = If(Value, 115, 86)
        End Set
    End Property
 
#End Region 'Properties
 
    Private Sub BackgroundWorkerForm_Shown(sender As Object, e As EventArgs) Handles Me.Shown
        'Start the background work when the form is displayed.
        BackgroundWorker1.RunWorkerAsync()
    End Sub
 
    Private Sub cancelWorkButton_Click(sender As Object, e As EventArgs) Handles cancelWorkButton.Click
        'Disable the button to prevent another click.
        cancelWorkButton.Enabled = False
 
        'Cancel the background work.
        BackgroundWorker1.CancelAsync()
    End Sub
 
    Private Sub BackgroundWorker1_ProgressChanged(sender As Object, e As ProgressChangedEventArgs)
        'Update the ProgressBar.
        ProgressBar1.Value = e.ProgressPercentage
    End Sub
 
    Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs)
        'Close the form when the work is done.
        Close()
    End Sub
 
End Class

Here's the code for the demo main form:

vb.net Code:

Imports System.ComponentModel
Imports System.Threading
 
Public Class Form1
 
    Private Sub BackgroundWorkerForm_DoWork(sender As Object, e As DoWorkEventArgs)
        'Simulate some time-consuming work.
        For i = 0 To 100
            Dim worker = DirectCast(sender, BackgroundWorker)
 
            If worker.CancellationPending Then
                e.Cancel = True
 
                Exit For
            End If
 
            If reportProgressCheckBox.Checked Then
                worker.ReportProgress(i)
            End If
 
            Thread.Sleep(100)
        Next
    End Sub
 
    'This method will be executed by the BackgroundWorker in the dialogue.
    Private Sub BackgroundWorkerForm_ProgressChanged(sender As Object, e As ProgressChangedEventArgs)
        statusLabel.Text = (e.ProgressPercentage / 100).ToString("p0")
    End Sub
 
    'This method will be executed by the BackgroundWorker in the dialogue.
    Private Sub BackgroundWorkerForm_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs)
        statusLabel.Text = If(e.Cancelled, "Operation cancelled", "Operation complete")
    End Sub
 
    Private Sub runButton_Click(sender As Object, e As EventArgs) Handles runButton.Click
        'Display the dialogue to initiate the background work.
        Using waitDialogue = GetWaitDialogue()
            waitDialogue.ShowDialog()
        End Using
    End Sub
 
    Private Function GetWaitDialogue() As BackgroundWorkerForm
        Dim dialogue As BackgroundWorkerForm
 
        'Only provide a ProgressChanged handler if the corresponding CheckBox is checked.
        If reportProgressCheckBox.Checked Then
            dialogue = New BackgroundWorkerForm(AddressOf BackgroundWorkerForm_DoWork,
                                                AddressOf BackgroundWorkerForm_ProgressChanged,
                                                AddressOf BackgroundWorkerForm_RunWorkerCompleted)
        Else
            dialogue = New BackgroundWorkerForm(AddressOf BackgroundWorkerForm_DoWork,
                                                AddressOf BackgroundWorkerForm_RunWorkerCompleted)
        End If
 
        'Only display a Cancel button if the corresponding CheckBox is checked.
        dialogue.SupportsCancellation = allowCancellationCheckBox.Checked
 
        Return dialogue
    End Function
End Class

Actually, there's one small mistake in the original code I posted. The BackgroundWorker1_ProgressChanged method should not have a Handles clause on it. It won't stop things working but it means that that method will be executed twice when progress is enable.

Great code! Thanks a bunch...

Thank you! Works in VS 2015 with .net 4.5.2 out of the box.

Thanks for the example, I have one more request that I think would help me understand the full circle. If I wanted to add a label in the BackgroundWorkerForm and update the label from Form1 during the background work to add a label showing textual work along with the progress bar. I tried a few things using invoke and begininvoke but have not had any luck. Care to expand? Thank you!

Quote:

---

Originally Posted by grapegummy

Thanks for the example, I have one more request that I think would help me understand the full circle. If I wanted to add a label in the BackgroundWorkerForm and update the label from Form1 during the background work to add a label showing textual work along with the progress bar. I tried a few things using invoke and begininvoke but have not had any luck. Care to expand? Thank you!

---

In the ProgressChanged event handler, the sender parameter is a reference to the wait dialogue. You can use that to access any members of that dialogue you like. If you want to be able to update a Label on that dialogue form then add a method that does that to the class and call it in that event handler.

Thank you!

If you have an existing project that you would like to add this wait dialogue to but you're not sure how, you can follow the instructions below.

1. Open the Solution Explorer, right-click your project and select Add -> Existing Item.
2. Navigate to the project folder for the demo project and select the BackgroundWorkerForm.vb file. The BackgroundWorkerForm type should be added to your project.
3. Open your own form and add the following field declaration to it, importing the System.ComponentModel namespace if required:

vb.net Code:

Private WithEvents BackgroundWorkerForm As BackgroundWorker

4. Use the navigation bar at the top of the code window to create the required event handlers.
4a. Select BackgroundWorkerForm in the middle drop-down and then select DoWork in the right-hand drop-down.
4b. Repeat the step above for ProgressChanged and RunWorkerCompleted if required.
5. Delete the field declaration that you added in step 3.
6. Delete the Handles clauses from the event handlers you created in step 4.
7. Add the appropriate code to each of the event handlers just as you would for any BackgroundWorker. If you intend for the dialogue's ProgressBar to display actual progress, your calls to ReportProgress must pass values in the range 0 to 100.
8. Where you want to display the dialogue and perform the work in your own code, create an instance of the BackgroundWorkerForm with the appropriate event handlers and show it, e.g.

vb.net Code:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Using waitDialogue As New BackgroundWorkerForm(AddressOf BackgroundWorkerForm_DoWork)
        waitDialogue.ShowDialog()
    End Using
End Sub

9. If you would like to be able to cancel the work before it completes, set the SupportsCancellation property to True, e.g.

vb.net Code:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Using waitDialogue As New BackgroundWorkerForm(AddressOf BackgroundWorkerForm_DoWork,
                                                   AddressOf BackgroundWorkerForm_ProgressChanged,
                                                   AddressOf BackgroundWorkerForm_RunWorkerCompleted) With {.SupportsCancellation = True}
        waitDialogue.ShowDialog()
    End Using
End Sub

Hello jmcilhinney, very useful code, thank you very much.
I tried it in combination of OpenFileDialog() but seems not working, there is an "Exception thrown: 'System.Threading.ThreadStateException' in System.Windows.Forms.dll" do you know how to resolve it ?

Quote:

---

Originally Posted by t0ret0s

Hello jmcilhinney, very useful code, thank you very much.
I tried it in combination of OpenFileDialog() but seems not working, there is an "Exception thrown: 'System.Threading.ThreadStateException' in System.Windows.Forms.dll" do you know how to resolve it ?

---

If it didn't work then you did it wrong. I don't know what you did so I have no idea what you did wrong. Did someone tell you I was psychic?

That said, why would you try it with an OpenFileDialog in the first place? The whole point of this is to give the user something to look at and provide feedback while work is performed in the background. How exactly is an OpenFileDialog background work?

Quote:

---

Originally Posted by jmcilhinney

If it didn't work then you did it wrong. I don't know what you did so I have no idea what you did wrong. Did someone tell you I was psychic?

That said, why would you try it with an OpenFileDialog in the first place? The whole point of this is to give the user something to look at and provide feedback while work is performed in the background. How exactly is an OpenFileDialog background work?

---

The idea is to check some files into the computer, in case the exact file is missing, I want to let user select it.
This is the first approach code :

Code:

---

        Dim worker = DirectCast(sender, BackgroundWorker)

        'Simulate some time-consuming work.
        For i = 0 To 100
            If worker.CancellationPending Then
                e.Cancel = True

                Exit For
            End If

            If reportProgressCheckBox.Checked Then
                worker.ReportProgress(i)
            End If

            If i = 50 Then

                If MsgBox("Do you want to select it manually ?", CType(vbYesNo + vbQuestion, Global.Microsoft.VisualBasic.MsgBoxStyle), "test test test test") = vbYes Then
                    Dim myStream As Stream = Nothing
                    Dim openFileDialog1 As New OpenFileDialog()

                    openFileDialog1.Title = "File " & "2_333333"
                    openFileDialog1.InitialDirectory = "C:\"
                    openFileDialog1.Filter = "pdf files (*.pdf)|*.pdf|All files (*.*)|*.*|" & ".Test" & "|*" & ".Test"
                    openFileDialog1.FilterIndex = 2
                    openFileDialog1.RestoreDirectory = True


                    openFileDialog1.ShowDialog() 'here the error is generated

                    If openFileDialog1.ShowDialog() = DialogResult.OK Then
                        Try
                            myStream = openFileDialog1.OpenFile()
                            If (myStream IsNot Nothing) Then
                                myStream.Close()
                                MsgBox(openFileDialog1.FileName)
                            End If
                        Catch Ex As Exception
                            MessageBox.Show("Cannot read file from disk. Original error: " & Ex.Message)
                        Finally
                            If (myStream IsNot Nothing) Then
                                myStream.Close()
                            End If
                        End Try
                    End If
                End If
            End If

            Thread.Sleep(100)
        Next

---

Another thing : if I use modal wait, is not possible to debug in case of error or exception, is it correct ?

Quote:

---

Originally Posted by t0ret0s

The idea is to check some files into the computer, in case the exact file is missing, I want to let user select it.
This is the first approach code :

Code:

---

        Dim worker = DirectCast(sender, BackgroundWorker)

        'Simulate some time-consuming work.
        For i = 0 To 100
            If worker.CancellationPending Then
                e.Cancel = True

                Exit For
            End If

            If reportProgressCheckBox.Checked Then
                worker.ReportProgress(i)
            End If

            If i = 50 Then

                If MsgBox("Do you want to select it manually ?", CType(vbYesNo + vbQuestion, Global.Microsoft.VisualBasic.MsgBoxStyle), "test test test test") = vbYes Then
                    Dim myStream As Stream = Nothing
                    Dim openFileDialog1 As New OpenFileDialog()

                    openFileDialog1.Title = "File " & "2_333333"
                    openFileDialog1.InitialDirectory = "C:\"
                    openFileDialog1.Filter = "pdf files (*.pdf)|*.pdf|All files (*.*)|*.*|" & ".Test" & "|*" & ".Test"
                    openFileDialog1.FilterIndex = 2
                    openFileDialog1.RestoreDirectory = True


                    openFileDialog1.ShowDialog() 'here the error is generated

                    If openFileDialog1.ShowDialog() = DialogResult.OK Then
                        Try
                            myStream = openFileDialog1.OpenFile()
                            If (myStream IsNot Nothing) Then
                                myStream.Close()
                                MsgBox(openFileDialog1.FileName)
                            End If
                        Catch Ex As Exception
                            MessageBox.Show("Cannot read file from disk. Original error: " & Ex.Message)
                        Finally
                            If (myStream IsNot Nothing) Then
                                myStream.Close()
                            End If
                        End Try
                    End If
                End If
            End If

            Thread.Sleep(100)
        Next

---

Another thing : if I use modal wait, is not possible to debug in case of error or exception, is it correct ?

---

That makes no sense at all. Like I said, the whole point of this is to give the user something to look at while the application is doing work in the background and they can't use the UI. If you expect them select a file using a dialogue then that is the very definition of using the UI so why are you even trying to use this dialogue or do anything in the background? There's no reason for you to be using this dialogue so don't. That is the last I will say on the matter.

Thank you, John