Author: Jonas Bilinkevicius 

I'm trying to restore/ set focus to my app after re-running the exe. I've tried 
using the Windows.Setfocus(FormHandle) command without success. I've also tried 
using ShowWindow. Doing this doesn't set focus to the window. If the the window is 
minimizied it restores it to the screen ok but the application still believes it is 
minimized, thus you can't minimize the window. You can overcome this by first right 
clicking the app's taskbar button and selecting restore. The minimize button then 
works correctly.

Answer:

You have to deal with the first instances Application window, not with the main 
form.
1   
2   {$R *.RES}
3   
4   function AlreadyRunning: Boolean;
5   var
6     wndmain, wndapp: HWND;
7   begin
8     wndmain := FindWindow('TMDIForm', nil);
9     {should really use a more unique classname}
10    result := wndmain <> 0;
11    if result then
12    begin
13      wndapp := GetWindowLong(wndmain, GWL_WNDPARENT);
14      if IsIconic(wndapp) then
15        SendMessage(wndapp, WM_SYSCOMMAND, SC_RESTORE, 0)
16      else
17        SetForegroundWindow(wndapp);
18    end;
19  end;
20  
21  begin
22    if AlreadyRunning then
23      Exit;
24    Application.Initialize;
25    Application.Title := 'J&S Library Manager';
26    Application.CreateForm(TMDIForm, MDIForm);
27    Application.CreateForm(TEditTextForm, EditTextForm);
28    Application.CreateForm(TOptionForm, OptionForm);
29    Application.CreateForm(TAboutBox, AboutBox);
30    Application.Run;
31  end.


I have a deep aversion against directly manipulating a window from outside, so I usually don't restore/show the first instances window from the second instance but instead send a message to the first instances main form and have it restore/show itself in a handler for the message. Using WM_COPYDATA it is also easy to pass on a commandline to the first instance this way.