Unique Instance Terminate Application

[Weitentaaal]

Hi,

i tried to use unique instance and put this in my on create of the main Form

Code: Pascal  [Select][+][-]

1.    if UniqueInstance.PriorInstanceRunning then begin
2.       //raise Exception.Create('Application already Running !');
3.       ShowMessage('Application already Running !');
4.       Close;
5.       Exit;
6.    end;
7.  

i do always get Access Violations. How do i correctly Terminate Application?

[bobby100]

This works for me in FormCreate:

Code: Pascal  [Select][+][-]

1. if UniqueInstance1.PriorInstanceRunning then
2.   begin
3.     Close;
4.   end;

And I also use this to bring the previous instance to the screen:

Code: Pascal  [Select][+][-]

1. procedure TfrmMain.UniqueInstance1OtherInstance(Sender: TObject;
2.   ParamCount: integer; const Parameters: array of string);
3. begin
4.   frmMain.WindowState := wsNormal;
5.   frmMain.Show;
6. end;

[Weitentaaal]

This works for me in FormCreate:

Code: Pascal  [Select][+][-]

1. if UniqueInstance1.PriorInstanceRunning then
2.   begin
3.     Close;
4.   end;

And I also use this to bring the previous instance to the screen:

Code: Pascal  [Select][+][-]

1. procedure TfrmMain.UniqueInstance1OtherInstance(Sender: TObject;
2.   ParamCount: integer; const Parameters: array of string);
3. begin
4.   frmMain.WindowState := wsNormal;
5.   frmMain.Show;
6. end;

Hey thanks !

works for me too but how do i avoid the Code to continue executing ? The Close wont stop my Application from still loading. i but the same Check ("UniqueInstance1.PriorInstanceRunning") in my Mainform in the OnClose and OnDestroy Events but something will still get executed.

"And I also use this to bring the previous instance to the screen"

didn't thought about this ! thanks, i will use it.

[Zvoni]

Hi,

i tried to use unique instance and put this in my on create of the main Form

Code: Pascal  [Select][+][-]

1.    if UniqueInstance.PriorInstanceRunning then begin
2.       //raise Exception.Create('Application already Running !');
3.       ShowMessage('Application already Running !');
4.       Close;
5.       Exit;
6.    end;
7.  

i do always get Access Violations. How do i correctly Terminate Application?

"Exit" exits the Function/Procedure this code is in.
You're probably looking for "Terminate"

[AlexTP]

Code: Pascal  [Select][+][-]

1. Application.Terminate; //better

or

Code: Pascal  [Select][+][-]

1. Halt; //not good for GUI apps

[Thaddy]

In my opinion testing for a Unique instance should be in the project.lpr file and before application.initialize and application.run are called.
In that case, though, you should not use showmessage, which relies on the LCL, but a native OS messagebox or not at all.
This pattern gives you the least amount of overhead.
Bail out as early as you can....

[Weitentaaal]

In my opinion testing for a Unique instance should be in the project.lpr file and before application.initialize and application.run are called.
In that case, though, you should not use showmessage, which relies on the LCL, but a native OS messagebox or not at all.
This pattern gives you the least amount of overhead.
Bail out as early as you can....

Thanks i didn't think of that. i will try to do it here

[Weitentaaal]

Added this Code to my lpr:

Code: Pascal  [Select][+][-]

1.    if InstanceRunning then begin
2.       Application.Terminate;
3.       Exit;
4.    end;
5.  

i thought after "Application.Terminate" was executed, all the Code after it would be ignored. It did not so thats why i was using the Exit in the first place.

[Zvoni]

Added this Code to my lpr:

Code: Pascal  [Select][+][-]

1.    if InstanceRunning then begin
2.       Application.Terminate;
3.       Exit;
4.    end;
5.  

i thought after "Application.Terminate" was executed, all the Code after it would be ignored. It did not so thats why i was using the Exit in the first place.

I‘d say that’s normal since it runs in its own thread and might have to do cleanup

Or just change your if clause to an if then else

If instance running then
  Terminate
Else
   Regular startup code

[KodeZwerg]

I guess in .lpr file I would do like

Code: Pascal  [Select][+][-]

1.   if not InstanceRunning then begin

followed by the basic code to initialize forms etc...

[Weitentaaal]

is it still possible to bring the already existing Application to screen when using the RAW version of it. Didn't find anything in the Unit itself.

[kwyan]

Because I want to bring the already existing Application to screen, I don't use I use EnumWindowsProc search for the existing Application and SetForegroundWindow API to set to Foreground.

Code: Pascal  [Select][+][-]

1. program MySample;
2.  
3. var
4.    HasUniqueProcess : boolean;
5.    
6. function EnumWindowsProc(wHandle: HWND; lParam: LPARAM): BOOL; export; stdcall;
7. type
8.    TWindowName = array[0..max_path] of WChar;
9. var
10.    cTitle : TWindowName;
11.    sTitle : string;
12. begin
13.    Result := true;
14.    cTitle := default(TWindowName);
15.    GetWindowTextW(wHandle, cTitle, MAX_PATH);
16.    sTitle := cTitle;
17.    if sTitle='My Sample' then
18.       begin
19.          SetForegroundWindow(wHandle);
20.          HasUniqueProcess := true;
21.          Result := false;
22.       end;
23. end;
24.  
25. function UniqueInstance : boolean;
26. begin
27.    HasUniqueProcess := false;
28.    EnumWindows(@EnumWindowsProc, 0);
29.    Result := HasUniqueProcess;
30. end;
31.  
32. begin
33.    if not UniqueInstance then
34.       exit;
35.  
36.    Application.Scaled := True;
37.    Application.Initialize;
38.    Application.CreateForm(TFrmMain, FrmMain); // FrmMain will set Main Form Caption to 'My Sample'
39.    Application.Run;
40. end.
41.  

Any one have better solution?

[d7_2_laz]

Not easier, but interesting though (but i guess it's Windows only):
I'm using the proposal as from reply #7 in:
https://forum.lazarus.freepascal.org/index.php/topic,27927.msg173384.html#msg173384

My special use case is that my app might be placed in more than one folder, where each one is dedicated for a special working context / config / data.
Here i'd want to allow the app running concurrently when started from different folders,
but to prohibit each one to be started twice from a same folder.
When started again from the same folder, it simply would be brought to foreground.
When started from a different folder, that should be allowed.

[kwyan]

So the magic is on folder name. I propose you change the Main Form Caption with folder name, e.g. : "My Sample (Folder1) " by using the following logic:

Code: Pascal  [Select][+][-]

1. function GenCaptionWithFolder : string;
2. var
3.    StartupPath : string;
4.    Index : integer;
5. begin
6.    StartupPath := ExtractFilePath(ParamStr(0));
7.    if (Length(StartupPath)>0) and (StartupPath[Length(StartupPath)]='\') then
8.       Delete(StartupPath, Length(StartupPath), 1);
9.    Index := RPos('\', StartupPath);
10.    if Index>0 then
11.       Delete(StartupPath, 1, Index);
12.    Result := 'My Sample (' + StartupPath + ')';
13. end;
14.  

Then you call this in Main Form activation:

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormActivate(Sender: TObject);
2. begin
3.    Caption := GenCaptionWithFolder;
4. end;  
5.  

You also call this in EnumWindowsProc when you compare the process's title with this value.

[d7_2_laz]

Previously I had temporarily considered this approach (via Caption), but didn't pursue it,
because i didn't want to be dependent on a form's caption for this. But that's surely a matter of taste of course. Fortunately multiple ways do exist ...