Problem with Keyboard hook proc
- by Steve
The background: My form has a TWebBrowser. I want to close the form with ESC but the TWebBrowser eats the keystrokes - so I decided to go with a keyboard hook.
The problem is that the Form can be open in multiple instances at the same time.
No matter what I do, in some situations, if there are two instances open of my form, closing one of them closes the other as well.
I've attached some sample code. Any ideas on what causes the issue?
var
EmailDetailsForm: TEmailDetailsForm;
KeyboardHook: HHook;
implementation
function KeyboardHookProc(Code: Integer; wParam, lParam: LongInt): LongInt; stdcall;
var
hWnd: THandle;
I: Integer;
F: TForm;
begin
if Code < 0 then
Result := CallNextHookEx(KeyboardHook, Code, wParam, lParam)
else begin
case wParam of
VK_ESCAPE:
if (lParam and $80000000) <> $00000000 then
begin
hWnd := GetForegroundWindow;
for I := 0 to Screen.FormCount - 1 do
begin
F := Screen.Forms[I];
if F.Handle = hWnd then
if F is TEmailDetailsForm then
begin
PostMessage(hWnd, WM_CLOSE, 0, 0);
Result := HC_SKIP;
break;
end;
end; //for
end; //if
else
Result := CallNextHookEx(KeyboardHook, Code, wParam, lParam);
end; //case
end; //if
end;
function TEmailDetailsForm.CheckInstance: Boolean;
var
I, J: Integer;
F: TForm;
begin
Result := false;
J := 0;
for I := 0 to Screen.FormCount - 1 do
begin
F := Screen.Forms[I];
if F is TEmailDetailsForm then
begin
J := J + 1;
if J = 2 then
begin
Result := true;
break;
end;
end;
end;
end;
procedure TEmailDetailsForm.FormCreate(Sender: TObject);
begin
if not CheckInstance then
KeyboardHook := SetWindowsHookEx(WH_KEYBOARD, @KeyboardHookProc, 0, GetCurrentThreadId());
end;
procedure TEmailDetailsForm.FormDestroy(Sender: TObject);
begin
if not CheckInstance then
UnHookWindowsHookEx(KeyboardHook);
end;
