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These days, most Windows applications seem to hide their main menu, and only reveal it after pressing the "Alt" key. Of course I wanted to implement this for one of my applications as well (Rename My TV series). Took me a while to figure it out and it's still not quite perfect.
The idea;
By default the main menu is not visible. Pressing the Alt key toggles it visible or not visible.
This method does just that, with one downside. Pressing Alt reveals the menu, but since it get's focus, you'll need to press the Alt key 2 or 3 times before it disappears again (the menu is doing stuff with the Alt key as well).
Step 1: Show/Hide the menu
On start I hide the menu as such:
self.Menu:=nil;
This effectively will disconnect the mainmenu from the form.
Making it visible is as simple as (assuming your menu is called MainMenu1):
self.Menu:=MainMenu1;
Step 2: Catching that Alt Key
This appears to be a little bit more complex and NOT CROSSPLATFORM!
You'll need to add the unit "windows" to your "uses" clause.
Add the following to the "private" section of your form:
procedure KeyMessage(Msg: LongWord; wParam:longint);
Add this right after the "implementation" keyword:
var
AltKeyHook: HHOOK;
function MessageHookProc(nCode: Integer; wParam: WPARAM; lParam: LPARAM): LRESULT; stdcall;
var
Msg: LCLType.PMsg absolute lParam;
begin
if nCode >= 0 then
case Msg^.message of
WM_KEYDOWN, WM_KEYUP, WM_SYSKEYDOWN, WM_SYSKEYUP, WM_CHAR, WM_SYSCHAR:
Form1.KeyMessage(Msg^.message, Msg^.wParam); // make sure to use the right form variable here!
end;
Result := CallNextHookEx(AltKeyHook, nCode, wParam, lParam);
end;
procedure TForm1.KeyMessage(Msg: LongWord; wParam:longint);
begin
if (Msg=WM_SYSKEYDOWN) and (wParam=18{=Alt key}) then
begin
if self.Menu=nil then// Toggle menu, assuming your MainMenu is called Mainmenu1
self.Menu:=MainMenu
else
self.Menu:=nil;
end;
end;
In the FormCreate event add:
AltKeyHook := SetWindowsHookEx(WH_GETMESSAGE, @MessageHookProc, 0, MainThreadID);
In the FormDestroy event add:
if AltKeyHook <> 0 then
begin
UnhookWindowsHookEx(AltKeyHook);
AltKeyHook := 0;
end;
And that's it ... 
Keep in mind, in the Keymessage function, you can also catch these "Msg" values: WM_KEYDOWN, WM_KEYUP, WM_SYSKEYDOWN, WM_SYSKEYUP, WM_CHAR, and WM_SYSCHAR. The "wParam" value holds the character or key code eg. IntToStr(wParam) of Chr(wParam).
