Access violation if i try to change the ribbon style using a TRibbonCombobox

Question

i get an Access Violation if i try to change the ribbon style using a TRibbonCombobox.

then, i modified the delphi ribbon demo to provide a combobox method to set the style:

1. added a TRibbonCombobox on the ribbon bar
2. added an event handler

here is the event code:

procedure TfrmRibbonDemo.RibbonComboBox1Change(Sender: TObject);

begin

  if RibbonComboBox1.Text='Luna' then

    Ribbon1.Style:=RibbonLunaStyle

    else

    Ribbon1.Style:=RibbonSilverStyle;

end;

when i change the style (especially more than once) with the TRibbonCombobox, i get:

date/time         : 2009-10-02, 11:11:29, 843ms
operating system  : Windows XP Service Pack 3 build 2600
physical memory   : 583/2047 MB (free/total)
free disk space   : (C:) 71.72 GB
display mode      : 1280x1024, 32 bit
allocated memory  : 23.59 MB
executable        : RibbonDemo.exe
exec. date/time   : 2009-10-02 11:11
compiled with     : Delphi 2009
madExcept version : 3.0k
exception class   : EAccessViolation
exception message : Access violation at address 0054767C in module 'RibbonDemo.exe'. Read of address 0000005F.

main thread ($ed0):
0054767c +054 RibbonDemo.exe RibbonActnCtrls           TCustomRibbonComboBox.SetBounds
00546e52 +0a2 RibbonDemo.exe RibbonActnCtrls           TRibbonComboControl.SetBounds
00516f39 +0f1 RibbonDemo.exe ActnMan                   TCustomActionControl.CalcBounds
0051853d +005 RibbonDemo.exe ActnCtrls                 TCustomButtonControl.CalcBounds
00546482 +00a RibbonDemo.exe RibbonActnCtrls           TRibbonComboControl.CalcBounds
00516754 +030 RibbonDemo.exe ActnMan                   TCustomActionControl.SetSpacing
0051a243 +01b RibbonDemo.exe ActnCtrls                 TCustomActionToolBar.CreateControl
00557f16 +01a RibbonDemo.exe Ribbon                    TCustomActionControlBar.CreateControl
0056205a +006 RibbonDemo.exe Ribbon                    TCustomRibbonGroup.CreateControl
0051243f +087 RibbonDemo.exe ActnMan                   TCustomActionBar.CreateControls
00519b35 +005 RibbonDemo.exe ActnCtrls                 TCustomActionDockBar.CreateControls
0051a2c6 +022 RibbonDemo.exe ActnCtrls                 TCustomActionToolBar.CreateControls
00557fcb +027 RibbonDemo.exe Ribbon                    TCustomActionControlBar.CreateControls
00562075 +005 RibbonDemo.exe Ribbon                    TCustomRibbonGroup.CreateControls
00514542 +05e RibbonDemo.exe ActnMan                   TCustomActionBar.RecreateControls
0050e081 +04d RibbonDemo.exe ActnMan                   TCustomActionManager.SetStyle
0055dac3 +02f RibbonDemo.exe Ribbon                    TCustomRibbon.SetStyle
0056720c +04c RibbonDemo.exe RibbonDemoMainForm 387 +3 TfrmRibbonDemo.RibbonComboBox1Change

if i make a style change with a button on the ribbon bar, it works fine.

thank you for your help!

Answer 1

You are modifying the styles of the ribbon, which also modifies the combobox that triggers the event.

In order for this to work, a programming interface must be "re-entrant", and the ribbon system obviously isn't.

There are several possible solutions:

• Do not modify the ribbon from a ribbon, move the configuration GUI to somewhere else.
• Make the combobox store the desired action somewhere and trigger another event that will be executed after the termination of your combobox event. For instance, you can set a TTimer with a very small interval (1), and then enable that timer in the combobox event, so that when the TTimer event is fired, the ribbon system can be modified according to the new choice without requiring a reentrant api.