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How to solve "Cross thread operation not valid"

, 7 Oct 2006 CPOL
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how to access a control from another thread which didn't create this control.
how to access a control from another thread which didn't create this control.

I faced this issue more than 1 time, I decided to collect info about it and made some changes on the code to simplify this problem to you cause it's really annoying and confusing to work with threading stuff. Here is a small code solves this problem FOREVER and in ANY case.

Error:

Cross thread operation not valid: Control "XXXXXXXXXX" accessed from a thread other than the thread it was created.

Solution:

1- Create your thread:

 Private Strt As System.Threading.Thread   


2- Start your thread wherever you want:

  Strt = New System.Threading.Thread(AddressOf MyThread1)
  Strt.Start()


3- Add the thread sub (MyThread1) and put whatever you want and remember that the lines which access a control from this thread will be separated to into another sub (the Delegate sub)

 Sub MyThread1
       ' Working code
       ' Working code
       ' Working code
       ' Working code
       ' Working code
       ' Working code

       AccessControl()

End Sub


From the previous code you will notice 2 things:
1st: AccessControl the sub which will be delegated.
2nd: ' Working code - which doesn't need a delegate to get it work. In other mean, it doesn't show up the error message you receive.

4- and finally, add the delegated sub:

Private Sub AccessControl()
        If Me.InvokeRequired Then
            Me.Invoke(New MethodInvoker(AddressOf AccessControl)) 
        Else
    ' Code wasn't working in the threading sub
    ' Code wasn't working in the threading sub
    ' Code wasn't working in the threading sub
    ' Code wasn't working in the threading sub
    ' Code wasn't working in the threading sub
            Button2.Visible = True
            Button3.Visible = True
            Opacity = 1
            ShowInTaskbar = True
        End If
    End Sub


From the previous code you will notice that all the codes which wasn't working in the threading sub will be added after "Else" line.
examples for some codes which needs to be delegated:
(Control).Visible
Me.Opacity
Me.ShowInTaskbar

I hope i simplified it enough, and now no worry about this issue again.
Special thanks to jmcilhinney for his help. You can also find this article at this link:
http://www.bitsnips.com/forums/viewtopic.php?p=102#102
Have a nice day Smile | :)

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Elagizy
Software Developer (Senior) InfraDrive
Egypt Egypt
Egyptian freelance programmer and the founder of InfraDrive, Inc.
 
Check:
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http://www.tufoxy.com
http://www.bitsnips.com
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Comments and Discussions

 
Generalthank u PinmemberMember 1116174114-Nov-14 3:22 
Generalyou are awesome!!! PinmemberjediYL2-Sep-14 20:07 
QuestionNo need to use Delagates PinmemberTino Fourie26-Jan-14 0:33 
GeneralMy vote of 5 Pinmemberthams13-Jul-13 9:24 
QuestionCross thread Pinmembersabuni5-Jan-13 12:05 
GeneralMy vote of 5 PinmemberDisactive16-Dec-12 6:52 
QuestionNice Article PinmemberSatish_Tijare21-Oct-12 20:57 
GeneralMy vote of 5 [modified] PinmemberOsama El Shammari24-Jul-12 12:30 
GeneralYou Rock! PinmemberTimmyTwins3-Jul-12 13:55 
GeneralRe: You Rock! PinmemberJoBrittain6-Jul-12 13:18 
QuestionMy vote Pinmemberkmf8-Dec-11 0:10 
GeneralMy vote of 5 Pinmembergafoor123-Nov-11 20:55 
QuestionAlternative Method Pinmemberjlopez78814-Oct-11 9:24 
GeneralMy vote of 5 PinmemberSunasara Imdadhusen9-Sep-11 4:19 
GeneralMy vote of 5 PinmemberNanda_MR14-Mar-11 0:34 
GeneralI laughed a lot :) PinmemberMember 102216227-Oct-10 0:17 
GeneralYou missed the point. PinmemberElagizy27-Oct-10 5:14 
GeneralMy vote of 5 PinmemberL3CodeProject22-Oct-10 11:47 
GeneralSimply Great!! Pinmemberrahu_12221-Sep-10 21:37 
Generalthanks :) :) PinmemberArunJoseph 471639512-Sep-10 6:30 
GeneralThank You Pinmemberjb.jigar30-Jul-10 9:39 
GeneralMy vote of 5 Pinmemberjb.jigar30-Jul-10 9:11 
QuestionWhat if the method is a handler of a PropertyChanged Event from an updated class variable? Pinmemberbretddog1-Apr-10 1:01 
AnswerRe: What if the method is a handler of a PropertyChanged Event from an updated class variable? PinmemberElagizy1-Apr-10 8:53 
GeneralIf it doesn't work for anyone try this... PinmemberMichaelsg23-Mar-10 0:14 
GeneralRe: If it doesn't work for anyone try this... PinmemberElagizy1-Apr-10 8:56 
GeneralWrap 'em up :) PinmemberDerek R. White13-Mar-10 16:27 
GeneralThat was absolutely great Pinmemberchowdarysway15-Oct-09 23:34 
GeneralAccess the controls in Thread PinmemberMuhammad Ghufran13-Aug-09 4:21 
JokeSimple and Clear !!! Pinmembermarcos_zanella15-Jul-09 19:29 
GeneralThanks...This is very useful Pinmemberpmlchan18-Jun-09 23:58 
GeneralMy vote of 2 PinmemberDanilo Corallo8-May-09 3:11 
Generalthanks a lot for the tip Pinmemberwyn4429-Oct-08 7:54 
General[Message Removed] PinmemberMojtaba Vali10-May-08 23:22 
GeneralVery Good! Pinmembertedpap8-Apr-08 21:18 
GeneralA lot of thanx man PinmemberMidhunlal G29-Nov-07 22:58 
GeneralI love you man!!!! PinmemberRanceDowner12349-Nov-07 13:07 
GeneralExcellent! PinmemberBogdan Rechi10-Oct-07 11:09 
GeneralGreat thanks !!! Pinmemberiskenderun9-Jul-07 22:30 
Questionwriting all the code in access control? [modified] PinmemberHari Om Prakash Sharma24-Jun-07 20:14 
AnswerRe: writing all the code in access control? Pinmemberelagizy24-Jun-07 21:57 
GeneralThanks again PinmemberElrond15-Jun-07 1:20 
GeneralOutstanding! PinmemberFabio Videira8-Jun-07 11:10 
GeneralIt simply works :-) PinmemberDiego F.24-May-07 5:58 
Generalcross thread operation Pinmemberevergreen50115-May-07 5:07 
Generalthis is easy yet brilliant Pinmembersunlight2-May-07 18:46 
QuestionPlease excuse my ignorance... PinmemberHD-P26-Apr-07 11:38 
I cannot seems to apply your solution to a little program I was looking at...
I would appreciate any help in this matter. I saw the "Dirty Fix", which worked, but I would rather know what I was really doing wrong.
 
The errors occur in the "Private Sub logchange" and "Private Sub logrename"
 
I am VERY new to the .NET world... Thanks again...
 
Imports System.IO
Imports System.Diagnostics
 
Public Class Form1
Inherits Form
 
Public watchfolder As FileSystemWatcher
 
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
 
End Sub
 
Private Sub btn_startwatch_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_startwatch.Click
watchfolder = New System.IO.FileSystemWatcher()
 
'this is the path we want to monitor
watchfolder.Path = Txt_watchpath.Text
 
'Add a list of Filter we want to specify
'make sure you use OR for each Filter as we need to
'all of those
 
watchfolder.NotifyFilter = IO.NotifyFilters.DirectoryName
watchfolder.NotifyFilter = watchfolder.NotifyFilter Or _
IO.NotifyFilters.FileName
watchfolder.NotifyFilter = watchfolder.NotifyFilter Or _
IO.NotifyFilters.Attributes
 
' add the handler to each event
AddHandler watchfolder.Changed, AddressOf logchange
AddHandler watchfolder.Created, AddressOf logchange
AddHandler watchfolder.Deleted, AddressOf logchange
 
' add the rename handler as the signature is different
AddHandler watchfolder.Renamed, AddressOf logrename
 
'Set this property to true to start watching
watchfolder.EnableRaisingEvents = True
 
btn_startwatch.Enabled = False
btn_stop.Enabled = True
 
'End of code for btn_start_click
 

End Sub
 
Private Sub logchange(ByVal source As Object, ByVal e As _
System.IO.FileSystemEventArgs)
'The following stops the Cross-Tread operation not valid - Error
'System.Windows.Forms.Control.CheckForIllegalCrossThreadCalls = False
 
If e.ChangeType = IO.WatcherChangeTypes.Changed Then
txt_folderactivity.Text &= "File " & e.FullPath & _
" has been modified" & vbCrLf
End If
If e.ChangeType = IO.WatcherChangeTypes.Created Then
txt_folderactivity.Text &= "File " & e.FullPath & _
" has been created" & vbCrLf
End If
If e.ChangeType = IO.WatcherChangeTypes.Deleted Then
txt_folderactivity.Text &= "File " & e.FullPath & _
" has been deleted" & vbCrLf
End If
 
'Reverse "Check for Illegal Cross Thread"
'System.Windows.Forms.Control.CheckForIllegalCrossThreadCalls = True
 
End Sub
 
Private Sub logrename(ByVal source As Object, ByVal e As _
System.IO.RenamedEventArgs)
'The following stops the Cross-Tread operation not valid - Error
'System.Windows.Forms.Control.CheckForIllegalCrossThreadCalls = False
 
txt_folderactivity.Text &= "File " & e.OldName & _
" has been renamed to " & e.Name & vbCrLf
'Reverse "Check for Illegal Cross Thread"
'System.Windows.Forms.Control.CheckForIllegalCrossThreadCalls = True
End Sub
 
Private Sub btn_stop_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_stop.Click
' Stop watching the folder
watchfolder.EnableRaisingEvents = False
btn_startwatch.Enabled = True
btn_stop.Enabled = False
 
End Sub
End Class
 

 


GeneralAny Solution for Same In .net 3.0 Pinmembersumit_4palz25-Apr-07 0:04 
GeneralRe: Any Solution for Same In .net 3.0 Pinmemberelagizy25-Apr-07 4:00 
AnswerRe: Any Solution for Same In .net 3.0 PinmemberMaxtorM1236-Nov-08 6:50 

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