How to capture KeyDown when focused controls interfere? - delphi

Question

I have a form with KeyPreview=true and want to capture the arrow keys, unless we are in a control that should handle those.
The issue is: focus is always on one of those controls.
How can I adapt/design this to work?
.PAS file
unit uKeyDownTests;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.ExtCtrls;
type
TFrmKeyDownTests = class(TForm)
PnlBottom: TPanel;
PnlClient: TPanel;
Edit1: TEdit;
Edit2: TEdit;
Edit3: TEdit;
procedure FormKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
private
public
end;
var
FrmKeyDownTests: TFrmKeyDownTests;
implementation
{$R *.dfm}
type
THackWinControl = class(TWinControl);
procedure TFrmKeyDownTests.FormKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
var lActiveControl: TControl;
begin
// Earlier code, but that did not work either:
// if Edit1.Focused or Edit2.Focused or Edit3.Focused then Exit;
lActiveControl := ActiveControl;
if Assigned(lActiveControl) then
begin
if lActiveControl = Edit1 then
begin
THackWinControl(Edit1).KeyDown(Key,Shift);
Exit;
end;
if lActiveControl = Edit2 then
begin
THackWinControl(Edit2).KeyDown(Key,Shift);
Exit;
end;
if lActiveControl = Edit3 then
begin
THackWinControl(Edit3).KeyDown(Key,Shift);
Exit;
end;
end;
if (Key = VK_RIGHT) then
begin
PnlBottom.Caption := PnlBottom.Caption + 'R';
Key := 0;
Exit;
end;
if (Key = VK_LEFT) then
begin
PnlBottom.Caption := PnlBottom.Caption + 'L';
Key := 0;
Exit;
end;
if (Key = VK_UP) then
begin
PnlBottom.Caption := PnlBottom.Caption + 'U';
Key := 0;
Exit;
end;
if (Key = VK_DOWN) then
begin
PnlBottom.Caption := PnlBottom.Caption + 'D';
Key := 0;
Exit;
end;
end;
end.
.DFM file
object FrmKeyDownTests: TFrmKeyDownTests
Left = 0
Top = 0
Caption = 'Keydown tests'
ClientHeight = 336
ClientWidth = 635
Color = clBtnFace
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = 'Tahoma'
Font.Style = []
KeyPreview = True
OldCreateOrder = False
OnKeyDown = FormKeyDown
PixelsPerInch = 96
TextHeight = 13
object PnlBottom: TPanel
Left = 0
Top = 295
Width = 635
Height = 41
Align = alBottom
TabOrder = 0
end
object PnlClient: TPanel
Left = 0
Top = 0
Width = 635
Height = 295
Align = alClient
TabOrder = 1
object Edit1: TEdit
Left = 40
Top = 32
Width = 121
Height = 21
TabOrder = 0
Text = 'Edit1'
end
object Edit2: TEdit
Left = 40
Top = 72
Width = 121
Height = 21
TabOrder = 1
Text = 'Edit1'
end
object Edit3: TEdit
Left = 40
Top = 112
Width = 121
Height = 21
TabOrder = 2
Text = 'Edit1'
end
end
end

Answer 1

(Answering my own question for my specific situation, slightly different from the one in the 'Possible dupe', but based on the answers there)
In my case, the easiest solution was:
procedure DialogKey(var Msg: TWMKey); message CM_DIALOGKEY; which only calls inherited
KeyPreview=true for the form
A FormKeydown that handles what I want to do with arrow keys
Result:
The controls that have focus as well as the form handle the arrow keys
It does not matter if the controls have an OnKeyDown handler (the Edit2 control) or not (the others)
Modified code:
unit uKeyDownTests;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.ExtCtrls;
type
TFrmKeyDownTests = class(TForm)
PnlBottom: TPanel;
PnlClient: TPanel;
Edit1: TEdit;
Edit2: TEdit;
Edit3: TEdit;
procedure FormKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
procedure Edit2KeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
private
procedure DialogKey(var Msg: TWMKey); message CM_DIALOGKEY; public
end;
var
FrmKeyDownTests: TFrmKeyDownTests;
implementation
{$R *.dfm}
procedure TFrmKeyDownTests.DialogKey(var Msg: TWMKey);
begin
inherited;
end;
procedure TFrmKeyDownTests.FormKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
case Key of
VK_RIGHT: PnlBottom.Caption := PnlBottom.Caption + 'R';
VK_LEFT : PnlBottom.Caption := PnlBottom.Caption + 'L';
VK_UP : PnlBottom.Caption := PnlBottom.Caption + 'U';
VK_DOWN : PnlBottom.Caption := PnlBottom.Caption + 'D';
end;
end;
{ TFrmKeyDownTests }
procedure TFrmKeyDownTests.Edit2KeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
PnlBottom.Caption := PnlBottom.Caption + '-kd-';
end;
end.