Multi Threading and VB.Net

[richkid]

hi..

i am fairly new to VB.Net and I have a form thats calling a crystal report. The report however takes a long time to load. i tried using Threads and I keep getting the following error : [ controls created on one thread cannot be parented to a control on another thread ] how can i solve this error. Any assistance is greatly appreciated

 
 
    Public docReport As New rptStatus
    Public invReport As New rptInventory
    Public useReport As New rptUser
    Public oReport As Object
    Public rType as String
 
 
  Private Sub frmReports_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
 
        If rType = "Inventory" Then
            oReport = invReport
        ElseIf rType = "Status" Then
            oReport = docReport
        Else
            oReport = useReport
            oReport.SetParameterValue(0, param3)
            oReport.SetParameterValue(1, param4)
            oReport.SetParameterValue(2, param1)
            oReport.SetParameterValue(3, param2)
        End If
 
        Dim repThread As New Thread(AddressOf loadReport)
        repThread.IsBackground = True
        repThread.Priority = ThreadPriority.Normal
        repThread.Start()
 
    End Sub
 
 
 
 Private Sub loadReport()
 
        Control.CheckForIllegalCrossThreadCalls = False
        cviewer.Visible = True
        Me.Cursor = Cursors.WaitCursor
        frmMain.tslCurrent.Text = "Loading Report ..."
        Application.DoEvents()
 
        Try
            Dim myTable As CrystalDecisions.CrystalReports.Engine.Table
            Dim myLogin As CrystalDecisions.Shared.TableLogOnInfo
 
            For Each myTable In oReport.Database.Tables
                myLogin = myTable.LogOnInfo
                myLogin.ConnectionInfo.Password = strPass
                myLogin.ConnectionInfo.UserID = strUser
                myLogin.ConnectionInfo.ServerName = strServer
                myLogin.ConnectionInfo.DatabaseName = strDatabase
                myTable.ApplyLogOnInfo(myLogin)
            Next
 
 
            '******************ERROR OCCURS HERE *******************************
            cviewer.ReportSource = oReport
            cviewer.ShowRefreshButton = False
 
        Catch ex As Exception
 
            MsgBox(ex.Message)
            frmMain.tslCurrent.Text = "Report not Loaded"
 
        Finally
            Me.Cursor = Cursors.Default
            'frmMain.tslCurrent.Text = ""
        End Try
    End Sub
 
 
 

[jhaxo]

In windows you can't access a gui element from any thread except the ui thread. Microsoft has provided something called delegates that your thread can invoke on the gui thread. A delegate is an object that can point to a function.

Here is a tutorial
http://www.codeproject.com/KB/vb/Delegate.aspx

I looked for one on this site. I am sure there is one but I didn't see it.

The basic idea is every Form has a method BeginInvoke so you need to :

1. Define a delegate

public delegate void MyDelegate(string mssg); //in c#.

2. instantiate a delegate

MyDelegate mydelegate = new ShowStatusDelegate(myfunction)

3. define the function pointed to by the delegate

void myfunction(string txt)
{
   textbox1.Text=txt;
}

4. now in your thread:

BeginInvoke(mydelegate,new object[]{"hello delegate world");

[richkid]

hi..
thanks for that post.... I tried it and I am now getting the report to show.. only problem is that Im back at the original problem because now I have to wait on the report to load before I can do anything :(