How do I create a single instance of MATLAB app (.mlapp file)?

I am using MATLAB 2017a and creating a GUI using app designer. However every time I run the app it creates a new instance of the GUI. GUIDE has a feature for creating singleton GUI. How do I achieve similar functionality with app designer.

Answer 1

[Jonathan Jacobs]

Here's (partially) my skanky hack. I place this in the startup function:

           set(0,'ShowHiddenHandles','on')
           ch = get(0,'Children');
           found=zeros(1,length(ch));
           keeper=zeros(1,length(ch));
           for i=1:length(ch)
              if strcmpi(ch(i).Name, 'EM Data Manager')
                 found(i)=i;
                 if strcmpi(ch(i).Tag,'EM Data Manager')
                    keeper(i)=i;
                 end
              end
           end

           if length(find(keeper>0)) > 1
              disp('Panic! Multiple keeper windows found!')
              keyboard
           elseif length(find(keeper>0))==1
              % control window already exists.
              ML_W_switch('mlw')
              figure(ch(keeper(keeper>0)))
              delete(app.EMDataManagerUIFigure)
              %close(app.EMDataManagerUIFigure)
              %clear app
              app=ch(keeper(keeper>0)).UserData;
              % doesn't go up the line back to orig caller.
              %assignin('caller','app',app);
           else
              % create new control window
              olddir=pwd;
              cd(findomprefs)
              scrsize=get(0,'ScreenSize');
              if exist('datamgr.mat','file')
                 load datamgr.mat wpos autofilt
                 try
                    app.auto_filt.Value = autofilt;
                 catch
                    app.auto_filt.Value = 1;
                 end
              else
                 wpos = [scrsize(3)/2 scrsize(4)/2];
              end
              try
                 cd(olddir)
              catch
              end
              cursize=app.EMDataManagerUIFigure.Position;
              newsize = [wpos(1:2) cursize(3) cursize(4)];
              app.EMDataManagerUIFigure.Position = newsize;
              app.loaded_data.UserData = app.f_info;
              app.EMDataManagerUIFigure.Tag = 'EM Data Manager';
              app.EMDataManagerUIFigure.NextPlot = 'new';
              app.EMDataManagerUIFigure.UserData = app;
              app.handholder.UserData = app;
          end

Basically, I check to see if there is a previous open instance. If there is, I grab its UserData (where I previously stored the original instance's 'app'). I delete the new instance and continue on using the previous 'app' structure.

It works fine, as long as you don't care about the handle that is returned when you call the mlapp. The NEW 'app' is deleted, and that is that all the middle-man functions between your mlapp's startupFcn and the call to it (either command line or from another function) only remember the NEW app, which was deleted. I tried assignin('caller'... but that only gets as far as the next level up in the caller stack.

Another option might be to regularly save all important values from the original instance and transfer them to the new instance before deleting the old instance.

It's a mess.

Answer 2

[Nitin Phadkule]

In design View of App designer you can select(enable) Single Running Instance Option in code options.

[stefano rota]

when calling again the app running in single instance from caller, it seems thar startupfnc in no more precessed in the called app. How can I update input arguments?