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IDProjectCategoryView StatusLast Update
0005225JEDI VCL00 JVCL Componentspublic2011-06-10 16:10
ReportergebyAssigned Toobones 
Status resolvedResolutionfixed 
Product VersionDaily / GIT 
Target VersionFixed in Version3.40 
Summary0005225: runtime designer surface - Issue with WM_WINDOWPOSCHANGED handling
DescriptionI have next mysterious issue with runtime designer surface. Sometimes my application crashed when user working with runtime designer. Crashes are mysterious like in ticket 0004912 and have same symptoms.

So, I try to see code around WM_WINDOWPOSCHANGED handling again. All seems to be fine when I remove UpdateDesigner call. IMHO it causing never-ending message loop in some cases and application crash.

Is this call of UpdateDesigner really needed? I not see any designer problems when I remove this line.

I am using Delphi 7. I not know if I am able to reproduce error as some public code. If I can, then I attach it later.

Thank you.
TagsNo tags attached.



2010-05-14 12:54

reporter   ~0017386

After some time I got exactly same error on my modified code too. Problem seems to be much deeper inside.

I try to debug code much better now. Interesting is - latest problem does not occur on W7. It crashing only on WinXP!

Crash is caused by neverending recursiva call of WM_WINDOWPOSCHANGED while user click on the control at designer surface. But on some specific content on the surface only, usually after load surface from the file.

But why? Current code for handling WM_WINDOWPOSCHANGED message do enumerate all controls on the surface and trying to find right one by comparing handles. Here is the problem hidden! Problem is caused by reading Control.Handle.

While Control does not have allocated handle yet, then TControl touch parent and try to allocate new handle. And somewhere here inside it generate next WM_WINDOWPOSCHANGED message. Maybe on some control only and in some specific situations only.

So, my final fix is easy - check 'HandleAllocated' first. Then I can return UpdateDesigner call removed in my first post and all still working fine.

My current code looks like:

                Control := TAccessWinControl(Container.Components[I]);
                if Control.HandleAllocated then //Added by me!
                  if PosChangedHandle = Control.Handle then
                    if not (csDestroyingHandle in Control.ControlState) then
                      {$IFDEF DELPHI10_UP}
                      {$ENDIF DELPHI10_UP}

Thank you for updating your sources.


2010-06-07 10:34

administrator   ~0017436

Thanks, this is now in SVN

Issue History

Date Modified Username Field Change
2010-04-21 11:08 geby New Issue
2010-05-14 12:54 geby Note Added: 0017386
2010-06-07 10:34 obones Note Added: 0017436
2010-06-07 10:34 obones Status new => resolved
2010-06-07 10:34 obones Fixed in Version => Daily / SVN
2010-06-07 10:34 obones Resolution open => fixed
2010-06-07 10:34 obones Assigned To => obones
2011-06-10 16:10 obones Fixed in Version Daily / SVN => 3.40