I want to minimize a Delphi application to the systray instead of the task bar.

The necessary steps seem to be the following:

1. Create icon which should then be displayed in the systray.
2. When the user clicks the [-] to minimize the application, do the following:
   1. Hide the form.
   2. Add the icon (step #1) to the systray.
   3. Hide/delete the application's entry in the task bar.
3. When the user double-clicks the application's icon in the systray, do the following:
   1. Show the form.
   2. Un-minimize the application again and bring it to the front.
   3. If "WindowState" is "WS_Minimized" set to "WS_Normal".
   4. Hide/delete the application's icon in the systray.
4. When the user terminates the application, do the following:
   1. Hide/delete the application's icon in the systray.

That's it. Right?

How could one implement this in Delphi?

I've found the following code but I don't know why it works. It doesn't follow my steps described above ...

unit uMinimizeToTray;

interface

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

const WM_NOTIFYICON = WM_USER+333; 

type
  TMinimizeToTray = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure CMClickIcon(var msg: TMessage); message WM_NOTIFYICON;
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  MinimizeToTray: TMinimizeToTray;

implementation

{$R *.dfm}

procedure TMinimizeToTray.CMClickIcon(var msg: TMessage);
begin
  if msg.lparam = WM_LBUTTONDBLCLK then Show;
end;

procedure TMinimizeToTray.FormCreate(Sender: TObject);
VAR tnid: TNotifyIconData;
    HMainIcon: HICON;
begin
  HMainIcon := LoadIcon(MainInstance, 'MAINICON');
  Shell_NotifyIcon(NIM_DELETE, @tnid);
  tnid.cbSize := sizeof(TNotifyIconData);
  tnid.Wnd := handle;
  tnid.uID := 123;
  tnid.uFlags := NIF_MESSAGE or NIF_ICON or NIF_TIP;
  tnid.uCallbackMessage := WM_NOTIFYICON;
  tnid.hIcon := HMainIcon;
  tnid.szTip := 'Tooltip';
  Shell_NotifyIcon(NIM_ADD, @tnid);
end;

procedure TMinimizeToTray.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action := caNone;
  Hide;
end;

end.