How to detect when the mouse move away from a TPanel in Delphi 6?

Question

I am using the OnMouseMove event to detect when the mouse pointer is over my TPanel, is there a way to know when the mouse pointer had moved away from it?

I need the panel to change colour when the mouse pointer is over it and return to its original colour once it moved away from it?

I am using Delphi 6 by the way.

Please help.

Best Regards.

Answer 1

You can use OnMouseEnter/OnMouseLeave event pair to detect mouse

procedure TForm1.Panel1MouseEnter(Sender: TObject);
begin
  Panel1.Caption:= 'IN';
  Panel1.Color:= clBlue;
end;

procedure TForm1.Panel1MouseLeave(Sender: TObject);
begin
  Panel1.Caption:= 'OUT';
  Panel1.Color:= clWhite;
end;

---

I can't test the following code in Delphi 6, but I hope it is OK

Updated

TrackMouseEvent code added - thanks to Sertac Akyuz answer

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls;

type
  TForm1 = class(TForm)
    Panel1: TPanel;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Panel1MouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
  private
    { Private declarations }
    FOldWndProc: TWndMethod;
    FMouseInPanel: Boolean;
    procedure PanelWndProc(var Message: TMessage);
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  FOldWndProc:= Panel1.WindowProc;
  Panel1.WindowProc:= PanelWndProc;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  Panel1.WindowProc:= FOldWndProc;
end;

procedure TForm1.Panel1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
var
  mEvnt: TTrackMouseEvent;
begin
  if not FMouseInPanel then begin
    mEvnt.cbSize := SizeOf(mEvnt);
    mEvnt.dwFlags := TME_LEAVE;
    mEvnt.hwndTrack := Panel1.Handle;
    TrackMouseEvent(mEvnt);
    Panel1.Caption:= 'IN';
    FMouseInPanel:= True;
  end;
end;

// if not defined in Delphi 6, WM_MOUSELEAVE = $02A3
procedure TForm1.PanelWndProc(var Message: TMessage);
begin
  if Message.Msg = WM_MOUSELEAVE then begin
    Panel1.Caption:= 'OUT';
    FMouseInPanel:= False;
  end;
  FOldWndProc(Message);
end;

end.

Answer 2

Yet another solution, using TrackMouseEvent to receive WM_MOUSELEAVE;

type
  TMyPanel = class(TPanel)
  private
    FMouseTracking: Boolean;
    FOnMouseLeave: TNotifyEvent;
    procedure WMMouseLeave(var Msg: TMessage); message WM_MOUSELEAVE;
  protected
    procedure MouseMove(Shift: TShiftState; X, Y: Integer); override;
  published
    property OnMouseLeave: TNotifyEvent read FOnMouseLeave write FOnMouseLeave;
  end;

procedure TMyPanel.MouseMove(Shift: TShiftState; X, Y: Integer);
var
  mEvnt: TTrackMouseEvent;
begin
  inherited;
  if not FMouseTracking then begin
    mEvnt.cbSize := SizeOf(mEvnt);
    mEvnt.dwFlags := TME_LEAVE;
    mEvnt.hwndTrack := Handle;
    TrackMouseEvent(mEvnt);
    FMouseTracking := True;
  end;
end;

procedure TMyPanel.WMMouseLeave(var Msg: TMessage);
begin
  Msg.Result := 0;
  FMouseTracking := False;
  if Assigned(FOnMouseLeave) then
    FOnMouseLeave(Self);
end;