TCustomControl: Focus erhalten wenn Programm aktiv wird

[TOndrej]

Zum Beispiel:

Delphi-Quellcode:

type
  TMyControl = class(TCustomControl)
  protected
    function MainWndHook(var Message: TMessage): Boolean;
    procedure Paint; override;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  end;

constructor TMyControl.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  if not (csDesigning in ComponentState) then
    Application.HookMainWindow(MainWndHook);
end;

destructor TMyControl.Destroy;
begin
  if not (csDesigning in ComponentState) then
    Application.UnhookMainWindow(MainWndHook);
  inherited Destroy;
end;

function TMyControl.MainWndHook(var Message: TMessage): Boolean;
begin
  case Message.Msg of
    CM_ACTIVATE,
    CM_DEACTIVATE:
      Invalidate;
  end;
  Result := False;
end;

procedure TMyControl.Paint;
const
  Colors: array[Boolean] of TColor = (clSilver, clRed);
begin
  Canvas.Brush.Color := Colors[(csDesigning in ComponentState) or  Application.Active];
  Canvas.Brush.Style := bsSolid;
  Canvas.FillRect(ClientRect);
end;