Catching ALL mouse events

Problem/Question/Abstract:

I tried to override the MouseDown() method in a subclass of TForm to get every event for a general handler.

Answer:

The Application.OnMessage event will see all mouse messages before they are delivered to the control under the mouse. You work at the API level there, however. If none of the controls needs to do special mouse processing just hook the same event to all OnMouse* events of interest.
The Sender parameter will tell you which control fired the handler.

Start with the example below:

  
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;

type
  TForm1 = class(TForm)
    ListBox1: TListBox;
    procedure FormCreate(Sender: TObject);
  private
    { private declarations }
    procedure MyMouseEvent(var Msg: TMsg; var Handled: Boolean);
  public
    { public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.MyMouseEvent(var Msg: TMsg; var Handled: Boolean);
var
  s: string;
begin
  case Msg.message of
    wm_LButtonDown: s := 'left mouse down';
    wm_LButtonUp: s := 'left mouse up';
    wm_MouseMove: s := 'mouse move';
  else
    s := '';
  end;
  if s <> '' then
    ListBox1.Items.Insert(0, s);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Application.OnMessage := MyMouseEvent;
end;

end.