Author: Jonas Bilinkevicius

I use a timer to check some conditions. If something special happens, I display a 
message form (using MyMessage.ShowModal, because I need an answer from the user). 
The timer goes on, so several of this Messages could be displayed simultaneously. 
What I want to do: Queue this messages and just display one. If the message is 
done, the next one is to be displayed.

Answer:

Simple idea: Instead of immediately popping up each message, queue them up into a 
stringlist. With a second timer (set to an appropriate interval) , process the 
message list, and delete/ take action. See example below (variations with enabling/ 
disabling timer2 are possible)

1   procedure TForm1.FormCreate(Sender: TObject);
2   begin
3     MsgList := TStringList.Create;
4   end;
5   
6   procedure TForm1.FormDestroy(Sender: TObject);
7   begin
8     MsgList.Free;
9   end;
10  
11  {check for abnormal conditions}
12  
13  procedure TForm1.Timer1Timer(Sender: TObject);
14  const
15    msgNumber: integer = 0;
16  begin
17    if Random > 0.5 then
18    begin
19      MsgList.Add('message ' + IntToStr(msgNumber) + ' @ ' + TimeToStr(Now));
20      inc(MsgNumber);
21    end;
22  end;
23  
24  {process messages}
25  
26  procedure TForm1.Timer2Timer(Sender: TObject);
27  begin
28    Timer2.Enabled := false; {extremely important !}
29    while MsgList.Count > 0 do
30    begin
31      {show oldest messages first}
32      ShowMessage(MsgList[0] + ' viewed @' + TimeToStr(Now));
33      MsgList.Delete(0);
34      {your specific actions ...}
35    end;
36    Timer2.Enabled := true;
37  end;