[RESOLVED] Threading - Add textboxes to form in thread

[Jova]

Hi,

I would like your help again, please.

I'm just getting to grips with threading. I'm trying to add 20 textboxes to a form.

I have 2 forms. The first one (form1) has a button 'Load textboxes'. This will take me to the second form (form2) where in the OnLoad event, it will create 20 textboxes and place it on form2.

Each time, it adds a textbox to the form, it refreshes form2.

I used Threading for this. I wish I could use Backgroundworker. I'm using Visual Studio 2005 with Pocket PC 2003. The language is Visual Basic.

Here's my code.

This is in my module modPocketPhone

Imports System.Threading
Imports System.ComponentModel

Module modPocketPhone

    Private oThreadStart As ThreadStart
    Private oThread As Thread


    Public Sub loadMytextBox()
        oThreadStart = New ThreadStart(AddressOf populateScreen)

        oThread = New Thread(oThreadStart)

        oThread.Start()

        Dim myTextBox As New TextBox
        myTextBox.Text = "Test"
        myTextBox.Top = 0
        myTextBox.Left = 30
        myTextBox.BackColor = Color.Red
        myTextBox.ForeColor = Color.White
        Form2.Controls.Add(myTextBox)
        Form2.Refresh()

    End Sub


    Public Sub populateScreen()
        Dim myTextBox As TextBox = Nothing
        Dim iHeight As Integer = 50
        Dim iWidth As Integer = 200

        Dim iTop As Integer = 0
        Dim iOffset As Integer = 6

        Dim i As Integer = 1
        Dim j As Integer = 20

        For i = 1 To j
            myTextBox = New TextBox
            myTextBox.Text = "Box " & i
            myTextBox.Height = iHeight
            myTextBox.Width = iWidth
            myTextBox.BackColor = Color.Azure
            myTextBox.Visible = True
            myTextBox.Left = 0

            If i > 0 Then
                myTextBox.Top = iHeight + iTop + iOffset
            End If

            Try
                Form2.Controls.Add(myTextBox)
                Form2.Refresh()
                Debug.WriteLine("Control  " & i)
            Catch ex As Exception
                Debug.WriteLine(ex.Message)
            End Try

        Next
    End Sub

End Module

I ran the code. I didn't get any errors shown through my debugging.

The above code is executed when form2 is loaded once the button in form1 is pressed. Form2 loads and fires up the procedure 'loadMyTextbox'. When it does, it creates a thread calling up up the procedure 'populateScreen'. This is where it creates the textboxes onscreen.

This is my Form2 code.

Public Class Form2

    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        loadMyTextBox()
    End Sub
End Class

I am doing this to create a questionnaire application. I noticed if I did not use Threading the process is quite intensive in loading controls to the screen. I can add a textbox to form2 without threading as you see in the lines followin 'oThread.Start'. I can see it on screen.

When the thread runs, I do not see any of my controls.

Can anyone please advise what I'm doing wrong?

[petevick]

Have you stepped through your code to see what is happening - that would be the first port of call.

It will take the same time to draw the controls using threading or not - why not just use a waitcursor?

[Jova]

I did the step through the code but it broke down on the line.

 Form2.Controls.Add(myTextBox)

It said 'No Source Code Available for the current Location'.

I copied two lines of code before and after the For...Next function.

MessageBox.Show(Form2.Controls.Count.ToString & " controls")

When it hits the first one, it says "0 controls" and after the For...next completes, I get a messagebox "20 controls". The controls are there but not seen.

[petevick]

Stepping through your code, your textboxes stay at the same place in the loop

Try

If i > 0 Then
myTextBox.Top = iHeight + iTop + iOffset
iTop += (iHeight + iOffset)
End If

[Jova]

Hi Pete,

Thanks for your help.

This morning, I decided to come back to this wee problem after learning a lot more about VB.Net. I realised now I needed a delegate to add the controls. When you run a thread, you need to access the Main form's thread to add a control (if that makes sense).

Maybe my solution below is not tidy but it works. I'm going to reuse this function as a template.

I created a new project as I no longer have the old project.

Create a new project and copy the code into your form1.vb file.

Public Class Form1

    ' FORM LOADING
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load

        ' CREATE THREAD AND START IT
        Dim trdAddTextBox As New Threading.Thread(AddressOf AddTextBox)
        trdAddTextBox.IsBackground = True
        trdAddTextBox.Start()

    End Sub

    ' CREATE DELEGATE
    Private Delegate Sub AddTextBoxDelegate()

    ' CREATE 5 TEXTBOXES
    Private Sub AddTextBox()
        If Me.InvokeRequired = True Then
            Dim d As New AddTextBoxDelegate(AddressOf AddTextBox)
            Me.Invoke(d)
        End If

        Dim i As Integer = 1
        Dim j As Integer = 5

        Dim iOffset As Integer = 25
        Dim iTop As Integer = 0

        For i = 1 To 5
            Dim myTextBox As New TextBox

            myTextBox.Width = 150
            myTextBox.Height = 50
            myTextBox.Top = iTop
            myTextBox.Left = 0
            myTextBox.Multiline = True
            myTextBox.Text = "Box " & i

            Try
                Me.Controls.Add(myTextBox)
            Catch ex As Exception
                'MessageBox.Show(ex.Message)
            End Try

            iTop += 55
        Next

    End Sub

End Class

This is my first foray into Threading.

[Shaggy Hiker]

There's a slightly easier way to call a sub in a different thread, especially in the UI thread. I'd have to search for a link, or you could. The search would be on my user name and SynchronizationContext.

Basically, each thread has a synchronization context, and you can make a SynchronizationContext variable and set it to the current context in the main thread. Then in other threads, if you call the Post method of that SynchronizationContext variable, you can pass it the address of the method you want to call, and that method will be called in the thread of the SynchronizationContext, which if you saved the context in the UI thread, would be the UI thread. Voila, you are calling a method in the UI thread from a background thread. This takes only a single line to save the SynchronizationContext, and a single line to call the Post method of the context.

[bhavin12300]

Hi Pete,

Thanks for your help.

This morning, I decided to come back to this wee problem after learning a lot more about VB.Net. I realised now I needed a delegate to add the controls. When you run a thread, you need to access the Main form's thread to add a control (if that makes sense).

Maybe my solution below is not tidy but it works. I'm going to reuse this function as a template.

I created a new project as I no longer have the old project.

Create a new project and copy the code into your form1.vb file.

Public Class Form1

    ' FORM LOADING
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load

        ' CREATE THREAD AND START IT
        Dim trdAddTextBox As New Threading.Thread(AddressOf AddTextBox)
        trdAddTextBox.IsBackground = True
        trdAddTextBox.Start()

    End Sub

    ' CREATE DELEGATE
    Private Delegate Sub AddTextBoxDelegate()

    ' CREATE 5 TEXTBOXES
    Private Sub AddTextBox()
        If Me.InvokeRequired = True Then
            Dim d As New AddTextBoxDelegate(AddressOf AddTextBox)
            Me.Invoke(d)
        End If

        Dim i As Integer = 1
        Dim j As Integer = 5

        Dim iOffset As Integer = 25
        Dim iTop As Integer = 0

        For i = 1 To 5
            Dim myTextBox As New TextBox

            myTextBox.Width = 150
            myTextBox.Height = 50
            myTextBox.Top = iTop
            myTextBox.Left = 0
            myTextBox.Multiline = True
            myTextBox.Text = "Box " & i

            Try
                Me.Controls.Add(myTextBox)
            Catch ex As Exception
                'MessageBox.Show(ex.Message)
            End Try

            iTop += 55
        Next

    End Sub

End Class

This is my first foray into Threading.

thanks.
this help me as well.

[Bajrang]

12334

[petevick]

Hi,
see this as an explanation of why you are getting that error