I’m trying to use events to update a textbox from a background worker from a different class.
It is the same problem as mentioned in this SO post, except I'm using VB.NET. I'm trying to implement the 2nd suggested solution by @sa_ddam213.
I’m getting an error: “Cross-thread operation not valid: Control 'txtResult' accessed from a thread other than the thread it was created on.”
Here is my code:
Public Class DataProcessor
Public Delegate Sub ProgressUpdate(ByVal value As String)
Public Event OnProgressUpdate As ProgressUpdate
Private Sub PushStatusToUser(ByVal status As String)
RaiseEvent OnProgressUpdate(status)
End Sub
Public Sub ProcessAllFiles(ByVal userData As UserData)
'Do the work
End Sub
End Class
Public Class MainForm
Private bw As New BackgroundWorker
Private dp As New DataProcessor
Private Sub bw_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
Dim worker As BackgroundWorker = CType(sender, BackgroundWorker)
If bw.CancellationPending = True Then
e.Cancel = True
Else
dp.ProcessAllFiles(CType(e.Argument, UserData))
End If
End Sub
Private Sub dp_OnProgressUpdate(ByVal status As String)
txtResult.Text = status
End Sub
Private Sub MainForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load
bw.WorkerReportsProgress = True
bw.WorkerSupportsCancellation = True
AddHandler bw.DoWork, AddressOf bw_DoWork
AddHandler bw.ProgressChanged, AddressOf bw_ProgressChanged
AddHandler bw.RunWorkerCompleted, AddressOf bw_RunWorkerCompleted
AddHandler dp.OnProgressUpdate, AddressOf dp_OnProgressUpdate
End Sub
End Class
Thanks all!
OneFineDay :
The event still comes from a different thread than the UI. You need to delegate the woke back to the UI. I don't check InvokeRequired because I know it is from the worker thread.\n\nMe is the form, Invoke asks for the delegate that will handle the work of bring the data to the UI thread. Here my Delegate Sub is a lambda Sub instead of using a normal Sub routine - simpler design.\n\nPrivate Sub dp_OnProgressUpdate(ByVal status As String)\n 'invoke the UI thread to access the control\n 'this is a lambda sub\n Me.Invoke(Sub\n 'safe to access the form or controls in here\n txtResult.Text = status\n End Sub)\n End Sub\n",
2015-04-06T17:08:59