Arrow key not working in component - delphi

Question

I use the Gecko SDK, a component that allows you to view web pages.
I use this component to create an html editor.
This problem happens when going off editing web pages.
The problem is that the arrow keys and the tab does not work with my component. I tried to find an answer to this problem, but I didn't find one. I found a track here, but the function does not work.
Function Movement (dx, dy) does not exist. Thank you for helping me solve this problem.
Procedure Tform1.TraiteMessages(Var msg : TMsg; Var Handled: boolean);
var
dx, dy : integer;
begin dx: 0; dy := 0;
With msg do
begin
IF Message = WM_KEYDOWN then
Case wparam of
VK_LEFT : dx := -1;
VK_RIGHT : dx := 1;
VK_UP : dy := -1;
VK_DOWN : dy := 1;
end;
end;
IF (dy = 0) AND (Dx = 0) then Handled := false else
begin
handled := true; // message traité
Mouvement(dx, dy) // exécution du tracé
end;
end;

Answer 1

Add this to your component's class:
procedure HandleDlgCode(var Msg:TMessage); message WM_GETDLGCODE;
and then in the implementation section:
procedure TComponentClass.HandleDlgCode(var Msg:TMessage);
var
M: PMsg;
begin
Msg.Result := DLGC_WANTALLKEYS or DLGC_WANTARROWS or DLGC_WANTCHARS or DLGC_HASSETSEL;
if Msg.lParam <> 0 then
begin
M := PMsg(Msg.lParam);
case M.message of
WM_KEYDOWN, WM_KEYUP, WM_CHAR:
begin
Perform(M.message, M.wParam, M.lParam);
Msg.Result := Msg.Result or DLGC_WANTMESSAGE;
end;
end;
end
else
Msg.Result := Msg.Result or DLGC_WANTMESSAGE;
end;
I've just copy-pasted this code from my own numeric editor, so it works.

Answer 2

This is not the way it is done!
This is the way we did things before Delphi, in 1996.
There no need for this complicated Windows stuff.
You are making an editor.
Delphi already has 2 editors build-in.
TMemo
TRichEdit.
Start with TMemo as your parent, and you have a ready made editor, no need to capture cursor keys.
interface
type
TMyComponent = class(TMemo)
// ^^^^^^^^^^^^^^^^^^^^<<- use this as your parent class
protected
procedure KeyPress(var Key: Char); override
...
implementation
procedure TMyComponent.KeyPress(var Key: Char);
begin
inherited;
//it works just like this, TMemo does everything.
end;
In fact you can leave out KeyPress and start working on other stuff.
No need to use lowlevel code. You are doing it too complex.
Get a book an delphi component design. Even for an older Delphi, not much has changed.
Every hour spend reading a book on this subject will save 20 hours of coding time.
Good luck.

Answer 3

Procedure Tform1.TraiteMessages(Var msg : TMsg; Var Handled: boolean);
var
dx, dy : integer;
begin
dx := 0;
dy := 0;
With msg do
begin
IF Message = WM_KEYDOWN then
begin
Case wparam of
VK_LEFT : dx := -1;
VK_RIGHT : dx := 1;
VK_UP : dy := -1;
VK_DOWN : dy := 1;
end;
end;
end;
Mouvement(dx, dy);
Handled := ((dy <> 0) or (dx <> 0));
end;
That cleans up your method... now, you should place a breakpoint on your IF statement, and another on your Case conditions to determine first and foremost if your message hook is ever being triggered, but also if the message being handled is what you would expect.
Does your component properly catch Key events? Do you have another visual component focused? Have you set your form's "KeyPreview" property to True?
You may also want to try using a TApplicationEvents control to deal with your key message hook (if your component is non-visual).
Take a look at this unit on my SVN repository (username and password are both "anon" without quotes) as it demonstrates how to intercept and handle key inputs even on non-visual components.
Hope this helps, and good luck!