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delphiinheritancekeypress

Delphi how to implement baseclass event?

I have an abstract Delphi XE form that acts as base class for a family of forms used in my application. I am trying to figure out the best way to make a help function (on F1 keypress) that opens a wiki-page for the active form.

I'd very much like this function to be implemented at base-class level and to call when the user presses F1 but I need some advice on how to do this in a smart way. Currently I just put a KeyDown-event on the base form but this gets overwritten if the subform receives its own KeyDown, at which point I have to manually call the baseKeyDown. Obviously, this is not optimal.. Is there a way to ensure I catch the F1 keypress at baseclass level, random overloads nonwithstanding?

I am running Delphi XE on Windows 7

Solution

  • You should override KeyDown method in your base form class.

    type
  TBaseForm = class(TForm)
  protected
    procedure KeyDown(var Key: Word; Shift: TShiftState); override;
  end;

procedure TBaseForm.KeyDown(var Key: Word; Shift: TShiftState);
begin
  // do your processing here
  // ...
  inherited; // call inherited method that will call OnKeyDown if assigned
end;

    This is default implementation of KewDown method that calls OnKeyDown events 

    procedure TWinControl.KeyDown(var Key: Word; Shift: TShiftState);
begin
  if Assigned(FOnKeyDown) then FOnKeyDown(Self, Key, Shift);
end;