How do I use uiopen in a class method?

I am new to Matlab, and trying to build a GUI. In App Designer, I dragged a Menubar to the window and copied the class definition to my app. Now I need to make it open a file using uiopen, I assume. Here is the OpenMenu component:

app.OpenMenu = uimenu(app.FileMenu);

app.OpenMenu.txt = 'Open';

app.OpenFile = uiopen; <---- doesn't work

The error message reads: Error using uiopen: Too many output arguments

What is the proper syntax to use uiopen, and where do I put it?

Answer 1

[Kurt]

Solution found: I needed a callback function.