All Directions At Once - Wed, 9 Dec 2009

Hi Louis

Regarding your shortcut problem, here’s a link that might be helpful:
http://www.codenewsfast.com/isapi/isapi.dll/article?id=9361D893&article=2318724

There are similar issues when using TFrame, by the way.

Regards
Uwe

Louis

Sorry, I just saw that the above link timed out. Here’s the original text:

> Does anyone understand when and how action lists fire?
> An application I’m working on (developed by others, so my intimate knowledge
> is limited) uses action lists as a methodology of invoking Fx key actions on
> various frames. This app has only the main form descending from the Tform
> class, everything else is something of the frame variety. Each module of
> the app has it’s own frame on which one or more other frames and panels
> live. Each module (frame) has an action list, a pop-up menu list and/or a
> number of toolbuttons.
> The problem arises when I want to do something different for, say.. the ‘F6′
> key, in one module than in another. If I start in one of the inner modules
> and press F6, the proper event fires most of the time. If I start in
> another module and press F6, the proper thing for that frame happens again.
> If I go back to the first module I tried and press F6 again, the action from
> the other module fires. This behavior occurs usually, but not all the time.
> Sometimes after a series of the above errors, the behavior starts acting as
> I would expect.

Tom,

key handling in Delphi is fairly complex. The sequence of events as they
relate to your question are:

- user hits a key, a keydown message is placed into the message queue
- Application.ProcessMessage gets it from the queue, feeds it through a
number of Application methods, one of these is IsKeyMsg.
- IsKeyMsg sends the key down as a CN_KEYDOWN message to the control
with focus.
- TwinControl.CNKeyDown calls TwinControl.IsMenuKey
- after checking the popup menu of the control (if any) for the shortcut
without success IsMenuKey locates the controls parent form and calls its
IsShortcut method.
- Tcustomform.IsShortcut first checks the forms menu, if any. If not
finding a matching shortcut it then walks over the action lists registered
with the form and calls each lists IsShortcut method, which in turn walks
over the actions in the list looking for a shortcut.
- If nobody wanted the key as shortcut yet a CM_APPKEYDOWN message is send to
the Application window for the key, TApplication.WndProc handles this by
calling the main forms IsShortCut (if the window is enabled only, not when
a modal form is up). Note that this means that the main forms IsShortcut
will be called twice if the active control is on the main form and the
key is not a shortcut!

The critical part for you is the sequence in which TCustomform.IsShortcut
walks over the action lists. A TFrame will add its TActionlist to the parent
forms actionlists list when the parent is assigned to its Parent property (see
TCustomFrame.SetParent) and remove it when the Parent changes or the
actionlist is destroyed. As far as i see the sequence of the actionlists does
not change afterwards. So if you have several enabled frames on your form
their action lists will be queried in the sequence the frames were added to
the form, so the form containing the active control may not be the first to be
queried.

What this boils down to is this: if you have colliding shortcuts that may act
differently on different frames on your form then you need to override the
forms IsShortcut method and take steps there to make sure the frame the active
control is on gets first crack at the shortcut. Something like this:

Function TMyform.IsShortcut( var Message: TWMKey): Boolean; { override }
Var
ctrl: TWinControl;
comp: TComponent;
i: Integer;
Begin
ctrl := ActiveControl;
If ctrl Nil Then Begin
Repeat
ctrl := ctrl.Parent
Until (ctrl = nil) or (ctrl Is TCustomframe);
If ctrl nil Then Begin
For i:= 0 To ctrl.componentcount-1 Do Begin
comp:= ctrl.Components[i];
If comp Is TCustomActionList Then Begin
result := TCustomActionList(comp).IsShortcut( message );
If result Then
Exit;
End;
End;
End;
End;
inherited;
End;

Untested!

For performance reason you may want to make sure the actionlist on each frame
is the first item created (set it to first in the designers createorder menu)
and you may also want to assume only one action list will be on a frame and
Exit the for loop once you found it, regardless of Result.

Louis

Glad I could help. I was dealing with the same problem as you just a few weeks ago and remembered where I found the solution. Speaking of: I’m not on StackOverflow, so I would appreciate if you could add the reference to the thread. Thanks.

The Delphi Pool: yeah, that was an old project of mine. Although it was very successful (1 million+ page views) I had to stop it because it was too time consuming. Pity, really.

> But, if you want to avoid things too “time consuming”, then you’ll do well to avoid StackOverflow

It’s not that I want to … I *have* to avoid things that are too time consuming. Running my own business eats up most of my time anyway.