EOutOfResources exception when trying to restore tray icon - delphi-xe

Question

I'm getting an EOutOfResources exception 'Cannot remove shell notification icon' when trying to implement code to restore the tray icon after an Explorer crash/restart. My code is based on the old solution found here. The exception occurs when trying to hide the trayicon. Why does the Delphi XE code below not work?
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ImgList, ExtCtrls;
type
TForm1 = class(TForm)
TrayIcon1: TTrayIcon;
ImageListTray: TImageList;
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
protected
procedure WndProc(var Message: TMessage); Override;
public
{ Public declarations }
end;
var
Form1: TForm1;
msgTaskbarRestart : Cardinal; {custom systemwide message}
implementation
{$R *.dfm}
//ensure systray icon recreated on explorer crash
procedure TForm1.FormCreate(Sender: TObject);
begin
msgTaskbarRestart := RegisterWindowMessage('TaskbarCreated');
end;
procedure TForm1.WndProc(var Message: TMessage);
begin
if (msgTaskbarRestart <> 0) and (Message.Msg = msgTaskbarRestart) then begin
TrayIcon1.Visible := False; {Destroy the systray icon here}//EOutOfResources exception here
TrayIcon1.Visible := True; {Replace the systray icon}
Message.Result := 1;
end;
inherited WndProc(Message);
end;
end.

Answer 1

The TTrayIcon.Visible property setter raises EOutOfResources when a NIM_DELETE request fails:
procedure TCustomTrayIcon.SetVisible(Value: Boolean);
begin
if FVisible <> Value then
begin
FVisible := Value;
...
if not (csDesigning in ComponentState) then
begin
if FVisible then
...
else if not (csLoading in ComponentState) then
begin
if not Refresh(NIM_DELETE) then
raise EOutOfResources.Create(STrayIconRemoveError); // <-- HERE
end;
...
end;
end;
end;
Where Refresh() is just a call to the Win32 Shell_NotifyIcon() function:
function TCustomTrayIcon.Refresh(Message: Integer): Boolean;
...
begin
Result := Shell_NotifyIcon(Message, FData);
...
end;
When you receive the TaskbarCreated message, your previous icons are no longer present in the Taskbar, so Shell_NotifyIcon(NIM_DELETE) returns False. When the Taskbar is (re-)created, you are not supposed to try to remove old icons at all, only re-add new icons with Shell_NotifyIcon(NIM_ADD) as needed.
TTrayIcon has a public Refresh() method, but that uses NIM_MODIFY instead of NIM_ADD, so that will not work in this situation, either:
procedure TCustomTrayIcon.Refresh;
begin
if not (csDesigning in ComponentState) then
begin
...
if Visible then
Refresh(NIM_MODIFY);
end;
end;
However, you don't actually need to handle the TaskbarCreated message manually when using TTrayIcon, because it already handles that message internally for you, and it will call Shell_NotifyIcon(NIM_ADD) if Visible=True:
procedure TCustomTrayIcon.WindowProc(var Message: TMessage);
...
begin
case Message.Msg of
...
else
if (Cardinal(Message.Msg) = RM_TaskBarCreated) and Visible then
Refresh(NIM_ADD); // <-- HERE
end;
end;
...
initialization
...
TCustomTrayIcon.RM_TaskBarCreated := RegisterWindowMessage('TaskbarCreated');
end.
If, for some reason, that is not working correctly, and/or you need to handle TaskbarCreated manually, then I would suggest calling the protected TCustomTrayIcon.Refresh() method directly, eg:
type
TTrayIconAccess = class(TTrayIcon)
end;
procedure TForm1.WndProc(var Message: TMessage);
begin
if (msgTaskbarRestart <> 0) and (Message.Msg = msgTaskbarRestart) then begin
if TrayIcon1.Visible then begin
// TrayIcon1.Refresh;
TTrayIconAccess(TrayIcon1).Refresh(NIM_ADD);
end;
Message.Result := 1;
end;
inherited WndProc(Message);
end;
Otherwise, simply don't use TTrayIcon at all. It is known to be buggy. I have seen a lot of people have a lot of problems with TTrayIcon over the years. I would suggest using Shell_NotifyIcon() directly instead. I have never had any problems using it myself.