Delphi custom button accel key

Question

I'm coding a custom button derived from tExCustomControl wich, in turn, is derived from tCustomControl. The tExCustomControl component, takes care of painting and showing the caption. I managed to display the caption with the accel char underlined, using WinAPI. How I can tell Windows that the accel key is associated with the tExButton, so it can handle the event?

Remy Lebeau Remy Lebeau · Accepted Answer · 2015-03-23T18:12:45

You don't tell Windows anything. When the user types an accelerator, Windows sends your app a WM_SYSCHAR message, which the VCL handles automatically. As the VCL searches for which control handles the accelerator, your component will receive a CM_DIALOGCHAR message, which you need to respond to, eg:

type
  TMyCustomButton = class(tExCustomControl)
  private
    procedure CMDialogChar(var Message: TCMDialogChar); message CM_DIALOGCHAR;
  end;

procedure TMyCustomButton.CMDialogChar(var Message: TCMDialogChar);
begin
  if IsAccel(Message.CharCode, Caption) and Enabled and Visible and
    (Parent <> nil) and Parent.Showing then
  begin
    Click;
    Result := 1;
  end else
    inherited;
end;

IsAccel() is a public function in the Vcl.Forms unit:

function IsAccel(VK: Word; const Str: string): Boolean;

It parses an accelerator from the provided Str value and compares it to the provided VK value.

The code above is exactly how TSpeedButton implements accelerators, for instance.

Delphi custom button accel key

1 Answers