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IDProjectCategoryView StatusLast Update
0005341JEDI VCL00 JVCL Componentspublic2012-02-29 16:53
ReportertetarddAssigned Toobones 
Status resolvedResolutionfixed 
Product VersionDaily / GIT 
Target VersionFixed in Version3.45 
Summary0005341: Add BeginUpdate/EndUpdate to TJvScrollBox
DescriptionTJvScrollBox are meant to receive controls, sometimes these are buid at run-time and that can have ugly flickering effect on the scroll box while it's being populated.

It would be nice to have BeginUpdate/EndUpdate procedures added to it that send a wm_SetRedraw message to block refreshing the display.

Should also apply to TPanel, if there is such a thing as a TjvPanel.

Additional Information
    FLockCount : Integer;


Procedure TJvScrollBox.BeginUpdate;
     If FLockCount = 1 Then
          SendMessage(Handle, wm_SetRedraw, Ord(False), 0);

Procedure TJvScrollBox.EndUpdate;
     If FLockCount = 0 Then
         SendMessage(Handle, wm_SetRedraw, Ord(True), 0);
TagsNo tags attached.



2010-09-30 00:09

developer   ~0017727

Did you have a sample showing this problem?

Kind regards


2010-09-30 10:30

reporter   ~0017728

My project is too big and confidential to send to you to illustrate it.

However, it can be easy to simulated:

Procedure TForm1.Button1Click(Sender : TObject);
   i : Integer;
     { Remove remark to fix the flicker: }
     // SendMessage(ScrollBox1.Handle, wm_SetRedraw, Ord(False), 0);
     For i := 1 To 1000 Do
          With TLabel.Create(Self) Do
               Parent := ScrollBox1;
               Left := 0;
               Top := i * 20;
          // Simulate lengthy configuring of the newly created TLabel control:
     { Remove remarks to fix the flicker: }
     // SendMessage(ScrollBox1.Handle, wm_SetRedraw, Ord(True), 0);
     // ScrollBox1.Refresh;

When I observed it, I googled for the problem to find a suggested answer and found that some others encountered it too and had to use the trick proposed above in their code (SendMessage with wm_SetRedraw, as shown above) so I thought that the components itself should handle the locking of refresh as suggested, using a BeginUpdate/EndUpdate mechanism (as is found in TListView).

NB: In essence, this should have been part of the VCL in the first place but Borland/CodeGear/Embarcadero didn't do a good job with that.


2010-09-30 15:42

reporter   ~0017730

OK, I found a problem with my suggestion. If your scroll box contains VCL controls, it works well but if it contains frames, they are not repainted, which is worse than the flicker so I suggest either ditch this suggestion and let's live with the flicker or somebody might know a way to repaint the frames fully (calling Invalidate/refresh for the scroll box or frames does not work).


2010-09-30 16:29

reporter   ~0017731

Found a possible solution: instead of calling Refresh after sending the wm_SetRedraw message, do:

RedrawWindow(ScrollBox1.handle, Nil, 0, RDW_ERASE or RDW_INVALIDATE or

The EndUpdate would then look like:

Procedure TJvScrollBox.EndUpdate;
     If FLockCount = 0 Then
         SendMessage(Handle, wm_SetRedraw, Ord(True), 0);
         RedrawWindow(ScrollBox1.handle, Nil, 0, RDW_ERASE or RDW_INVALIDATE or


2010-10-08 16:40

administrator   ~0017841

I'm sorry, but if would make our testing easier if you could provide the zipped sources of a sample application showing this

2010-10-12 13:36


Demo JvScrollBox (562,382 bytes)


2010-10-12 13:38

reporter   ~0017877

I uploaded a demo. Simply run it and execute it with and without the check box ticked (to use or not a BeginUpdate/EndUpdate mechanism). Also in the zip file is my proposed changes to TJvScrollBox that was used to create the demo.


2010-11-09 15:10

administrator   ~0018060

Thanks, this is now integrated in SVN.
Next time, please to try to respect the JVCL style guide, it will make integration easier.

Issue History

Date Modified Username Field Change
2010-09-29 18:01 tetardd New Issue
2010-09-30 00:09 jfudickar Note Added: 0017727
2010-09-30 00:09 jfudickar Status new => feedback
2010-09-30 10:30 tetardd Note Added: 0017728
2010-09-30 15:42 tetardd Note Added: 0017730
2010-09-30 16:29 tetardd Note Added: 0017731
2010-10-08 16:40 obones Note Added: 0017841
2010-10-12 13:36 tetardd File Added: Demo JvScrollBox
2010-10-12 13:38 tetardd Note Added: 0017877
2010-11-09 15:10 obones Note Added: 0018060
2010-11-09 15:10 obones Status feedback => resolved
2010-11-09 15:10 obones Fixed in Version => Daily / SVN
2010-11-09 15:10 obones Resolution open => fixed
2010-11-09 15:10 obones Assigned To => obones
2012-02-29 16:53 obones Fixed in Version Daily / SVN => 3.45