How to stop TRadioButton reacting at arrow keys? - delphi

Question

I have a panel with a few TRadioButtons placed horizontally. If the most left button is focused and I press Left Arrow, the focus jumps to the most right button. I want to stop this behavoir for all arrows when they reach the edge. Is it possible ?
I tried overriding the WM_KEYDOWN but the buttons never receive this message when a arrow key is pressed.
TRadioButton = class(StdCtrls.TRadioButton)
protected
procedure WMKeyDown(var Message: TWMKeyDown); message WM_KEYDOWN;
procedure WMKeyUp(var Message: TWMKeyUp); message WM_KEYUP;
public
BlockLeft, BlockRight: Boolean;
constructor Create(AOwner: TComponent); override;
end;
constructor TRadioButton.Create(AOwner: TComponent);
begin
inherited;
BlockLeft:= False;
BlockRight:= False;
end;
procedure TRadioButton.WMKeyDown(var Message: TWMKeyDown);
begin
if BlockLeft and (Message.CharCode = VK_LEFT) then Exit;
if BlockRight and (Message.CharCode = VK_RIGHT) then Exit;
inherited;
end;
procedure TRadioButton.WMKeyUp(var Message: TWMKeyUp);
begin
if BlockLeft and (Message.CharCode = VK_LEFT) then Exit;
if BlockRight and (Message.CharCode = VK_RIGHT) then Exit;
inherited;
end;

Answer 1

VCL offsets keyboard messages to become a control notification and sends it to the message's destined control. Hence you should be intercepting a CN_KEYDOWN message instead.
If this is for a one time design consideration, I would prefer to handle this behavior at the form level since IMO a control, itself, shouldn't care where it is placed on. For a form where all radio buttons are expected to behave similar, an example could be:
procedure TForm1.CMDialogKey(var Message: TCMDialogKey);
begin
if ActiveControl is TRadioButton then
case Message.CharCode of
VK_LEFT, VK_UP: begin
if ActiveControl.Parent.Controls[0] = ActiveControl then begin
Message.Result := 1;
Exit;
end;
end;
VK_RIGHT, VK_DOWN: begin
if ActiveControl.Parent.Controls[ActiveControl.Parent.ControlCount - 1]
= ActiveControl then begin
Message.Result := 1;
Exit;
end;
end;
end;
inherited;
end;
If this is not for a one time behavior, I'd go for writing a container control as Victoria mentioned in the comments to the question.