Sample project screenshot. Windows 7

NB #2 All manipulatations with taskbar buttons must be done after button will be created, to catch this moment we should subscribe to WM_TASKBARBUTTONCREATED event, that must firstly registered by RegisterWindowMessage(‘TaskbarButtonCreated’); – I reccomend you to add this registration to initialization section of unit with your form:

//.....//
initialization
  WM_TASKBARBUTTONCREATED := RegisterWindowMessage('TaskbarButtonCreated');
end.

NB #3 You must be sure that Application.MainFormOnTaskbar is True; or drop on form TLMDFormVista for delphi 6-2005 versions

Now, when we registered message we can handle it in WndProc method to setup taskbar button:

type
  TForm8 = class(TForm)
    Timer1: TTimer;
    ImageList1: TImageList;
    ProgressBar1: TProgressBar;
    procedure FormCreate(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    FTick: Int64;
    FButtons: array[0..2] of TThumbButton;
    FNormalIcon: Cardinal;
    FPauseIcon: Cardinal;
    FTaskBar: ITaskbarList3;
  protected
    procedure WndProc(var Message: TMessage); override;
    { Private declarations }
  public
    { Public declarations }
  end;
//...//
procedure TForm8.WndProc(var Message: TMessage);
begin
  inherited;
  // Is tasbar button created?
  if Message.Msg = WM_TASKBARBUTTONCREATED then
  begin
    // Create instance of ITaskbarList3
    CoCreateInstance(CLSID_TaskbarList, nil, CLSCTX_INPROC_SERVER, IID_ITaskbarList3, FTaskBar);
    // Init
    FTaskBar.HrInit;
    // This method set progress state of tasbar button.
    // Button has next states: error, paused, normal and indetermintate
    FTaskBar.SetProgressState(Handle, TBPF_NORMAL);
    FNormalIcon := LoadIcon(0, IDI_ASTERISK);
    FPauseIcon := LoadIcon(0, IDI_WARNING);
    // Set overlay icon for taskbar button - "!" - asterix
    FTaskBar.SetOverlayIcon(Handle, FNormalIcon, 'In progress');

    // Buttons setup
    // Set imagelist handle that contains glyphs for our buttons
    FTaskBar.ThumbBarSetImageList(Handle, ImageList1.Handle);
    // This identificator will be used to determinate what button pressed
    FButtons[0].iId := 40001;
    FButtons[0].dwFlags := THBF_ENABLED;
    FButtons[0].iBitmap := 0;
    StringToWideChar('Reset', FButtons[0].szTip, 260);
    FButtons[0].dwMask := THB_BITMAP or THB_FLAGS or THB_TOOLTIP;

    FButtons[1].iId := 40002;
    FButtons[1].dwFlags := THBF_DISABLED;
    FButtons[1].iBitmap := 1;
    StringToWideChar('Play', FButtons[1].szTip, 260);
    FButtons[1].dwMask := THB_BITMAP or THB_FLAGS or THB_TOOLTIP;

    FButtons[2].iId := 40003;
    FButtons[2].dwFlags := THBF_ENABLED;
    FButtons[2].iBitmap := 2;
    StringToWideChar('Pause', FButtons[2].szTip, 260);
    FButtons[2].dwMask := THB_BITMAP or THB_FLAGS or THB_TOOLTIP;
    // Add buttons to thumbnail
    FTaskBar.ThumbBarAddButtons(Handle, 3, @FButtons[0]);
    FTaskBar.SetThumbnailTooltip(Handle, 'Test');
    Timer1.Enabled := True;
  end;
end;

To handle buttons click we need to catch WM_COMMAND message, WParamLo field will contains id of clicked button:

procedure TForm8.WndProc(var Message: TMessage);
begin
  //...//
  if Message.Msg = WM_COMMAND then
  begin
    // Handle 'Reset' button
    if Message.WParamLo = 40001 then
    begin
      Timer1.Enabled := True;
      FTaskBar.SetProgressState(Handle, TBPF_NORMAL);
      FTick := 0;
    end;
    // Handle 'Play' button
    if Message.WParamLo = 40002 then
    begin
      // Run timer again
      Timer1.Enabled := True;
      FTaskBar.SetProgressState(Handle, TBPF_NORMAL);
      // Set overlay icon to asterix icon
      FTaskBar.SetOverlayIcon(Handle, FNormalIcon, 'In progress');
      ProgressBar1.State := pbsNormal;
      // Disable 'Play' button
      FButtons[1].dwFlags := THBF_DISABLED;
      // Enable 'Pause' button
      FButtons[2].dwFlags := THBF_ENABLED;
      // Update buttons
      FTaskBar.ThumbBarUpdateButtons(Handle, 3, @FButtons[0])
    end;
    // Handle 'Pause' button. Almost the same as for 'Play'
    if Message.WParamLo = 40003 then
    begin
      Timer1.Enabled := False;
      FTaskBar.SetProgressState(Handle, TBPF_PAUSED);
      FTaskBar.SetOverlayIcon(Handle, FPauseIcon, 'Paused');
      ProgressBar1.State := pbsPaused;
      FButtons[1].dwFlags := THBF_ENABLED;
      FButtons[2].dwFlags := THBF_DISABLED;
      FTaskBar.ThumbBarUpdateButtons(Handle, 3, @FButtons[0])
    end;
  end;
end;

And finally OnTimer handler code:

procedure TForm8.Timer1Timer(Sender: TObject);
begin
  FTaskBar.SetProgressValue(Handle, FTick, 200);
  ProgressBar1.Position := FTick;
  Inc(FTick);
  // It's all?
  if FTick >= 200 then
  begin
    // Set indeterminate progress mode for tasbar button
    FTaskBar.SetProgressState(Handle, TBPF_INDETERMINATE);
    Timer1.Enabled := False;
  end;
end;

That’s all for “Part 1″ – I hope that it will be useful for someone.