You dont have to use setappdata, getappdata in app designer.
You can store the values that you want to be available in your app as public or private properties.
You need to add the properties to your app in the GUI before you use them.
These can then be accessed in your function as follows.
function somefunction(app)
app.Propertyname = 12;
end
function someotherfunction(app)
disp(app.Propertyname);
end
