How Do I Cross-Threading Help

Question

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Hello everyone, im really sorry if i did anything wrong, i just don't know how to make this thing works !

So everyone here's the class i made it to store the logs into TextBox / txt.

VB

Public Class EventLogger

#Region " Events "
     Public Event EntryWritten As EntryWrittenEventHandler
    Public Delegate Sub EntryWrittenEventHandler(x As String)

#End Region

#Region " Methods "
     Sub WriteEntry([Text] As String)
        Try
           My.Computer.FileSystem.WriteAllText("D:\log.txt", [Text], True)
           RaiseEvent EntryWritten([Text])
        Catch ex As Exception
            Debug.Print(ex.Message)
        End Try
    End Sub

#End Region

End Class

Usage :

VB

Public Class frmMain

  Public Logger As New EventLogger


   Private Sub frmMain_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        AddHandler Logger.EntryWritten, AddressOf OnEntryWritten

        Logger.WriteEntry("Application initialized.")
        'This Works

         Threading.ThreadPool.QueueUserWorkItem(AddressOf Start)
    End Sub

    Private Sub OnEntryWritten(x As String)
        EventLog.Text = x
    End Sub

    Sub Start()

'Cross-thread operation not valid: Control 'EventLog' accessed from a thread other than the thread it was created on.

        Logger.WriteEntry(-1, "hello")

    End Sub

End Class

Anyone can help me ?

Thank you everyone.

Posted 24-Apr-14 12:15pm

nazarinlaw

Updated 24-Apr-14 13:00pm

v3

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Comments

Dave Kreskowiak 24-Apr-14 18:29pm

Why are you even raising an event?

Sergey Alexandrovich Kryukov 24-Apr-14 18:42pm

Good question. The purpose is really unclear, as well as the whole question.
I answered in a very general but detailed way, please see.
—SA

nazarinlaw 24-Apr-14 18:49pm

I raised an event to update my textbox bro !

Sergey Alexandrovich Kryukov 24-Apr-14 19:19pm

It does not explain it. To update something, you just need to Invoke it.
—SA

Dave Kreskowiak 24-Apr-14 23:57pm

First, don't call anyone you don't know "bro".

Second, in what you've posted, there's no reason you need an event at all. You just need to Invoke a function on the UI thread to update the TextBox.

As a side, if your log has more than a few messages in it, the TextBox is a terrible control to use. The string you keep appending to is being reallocated over and over again each time you log a message. Use a ListBox instead.

nazarinlaw 25-Apr-14 4:33am

Ok dude, let me have the class if you don't mind ! it only take 2 min for you ! :)

Dave Kreskowiak 25-Apr-14 7:10am

I'm not writing your code for you.

nazarinlaw 25-Apr-14 9:28am

Nevermind then !

nazarinlaw 24-Apr-14 18:53pm

Are you there ?

nazarinlaw 24-Apr-14 18:39pm

Thank you for reply, im about to update the textbox whenever i write.entry using multithread on different classes.

Example:

Module Program

Public Logger as New EventLogger

Sub Initialize()
AddHandler Logger.EntryWritten, AddressOf OnEntryWritten

End Sub

Private Sub OnEntryWritten(x As String)
frmMain.EventLog.Text = x
End Sub

End Module

I Update my Textbox from different class

Logger.WriteEntry("Something")

Sorry if iam wrong, is there anyother way to do that ! instead of using timer ?

nazarinlaw 24-Apr-14 18:47pm

@Experts

I just want to update my textbox from different classes ? how can i suppose to do that if im running in thread ?

[no name] 24-Apr-14 19:14pm

Well if you had actually read Sergey's answer you would have found many ways. Probably the one you would find easiest is http://msdn.microsoft.com/en-us/library/zyzhdc6b(v=vs.110).aspx

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Sergey Alexandrovich Kryukov · Accepted Answer · 2014-04-24T12:41:00

Solution 1

There is no such concept as "invoke in class". This is irrelevant. It's important in what thread you are running some code. There are two very different cases: if you need to invoke some operation to a UI thread, or to do it in some custom thread. I answered both question in detail in my past answer:
.NET event on main thread[^].

For the detailed explanation of the mechanisms involved, see my article referenced in that answer with some comments on it. Please see: Simple Blocking Queue for Thread Communication and Inter-thread Invocation[^].

—SA

Posted 24-Apr-14 12:41pm

Sergey Alexandrovich Kryukov

Comments

nazarinlaw 24-Apr-14 18:58pm

Sorry im rejecting this answer for just getting your attention ! please don't take this wrong :(

Sergey Alexandrovich Kryukov 24-Apr-14 19:19pm

No problem at all, but I still think this is all you really need. You just need to use this information properly.
If you have any follow-up question, you are quite welcome to ask them.
—SA

nazarinlaw 24-Apr-14 19:51pm

Thank you bro, please look at the code below and let me know is it correct or do i have to lock the object to perform the threads to update my textbox without any further issue ?

nazarinlaw 24-Apr-14 19:45pm

I think that i figured it out bro ! please tell me if im wrong :)

Public Class EventLogger

#Region " Methods "

Public Target As Control
Sub AssignControl(c As Control)
Target = c
End Sub

Private Delegate Sub WriteEntryDelegate(Index As Integer, [Text] As String)
Sub WriteEntry(Index As Integer, [Text] As String)
Try
If Target.InvokeRequired Then
Target.Invoke(New WriteEntryDelegate(AddressOf WriteEntry), Index, [Text])
Else
Target.Text &= "Thread: " & Index & [Text]
End If
Catch ex As Exception
Debug.Print(ex.Message)
End Try
End Sub

#End Region

End Class

Sergey Alexandrovich Kryukov 24-Apr-14 21:29pm

More or less...
Let's see:

AssignControl is pointless and Target is bad style. Should be, say, private-write public-read property instead (or whatever you need). Public fields means bad style, should be properties. Pretty obvious why.

InvokeRequired is only needed if called from the thread rather then UI. If this is the UI thread, no invoke needed. I have no idea in what thread are you going to call it...

—SA

nazarinlaw 25-Apr-14 4:13am

Ok dude, can you just get me full class if you don't mind ?

nazarinlaw 25-Apr-14 9:29am

Nevermind then i don't know how to do that, as long as it works ! there won't be any issue !

Thank you buddy