How could I get the handler of an uiobject inside a function?

For example, I have this script main:

In main I call a function( func1) that creates a figure and some uiobjects;

func1 should looks like this:

function [return1,return2]= func1(arg1,arg2,arg3,etc) 
figure('Name','notRelevant',...
    'Units','normalized',...
    'Position',[0.1 0.2 0.7 0.6],...
    'NumberTitle','off','color','#B2BABB');
%uipanel
--
%
uicontrol('Style','PopupMenu',...
    'Units','normalized',...
    'Position',[0.26 0.48 0.1 0.15],...
    'String',someString,...
    'Value','1',...,
    'Tag','d',...
    'Callback','func2(neededHandler)',...
    'Parent',Rgr);%I have the buttons in an ui panel
neededHandler=uicontrol('Style','PopupMenu',...
    'Units','normalized',...
    'Position',[0.26 0.68 0.1 0.15],...
    'String',string1,...
    'Value',1,...,
    'Tag','d',...
    'Callback','',...
    'Parent',Rgr);
end

Inside func2:

function func2(neededHandler)
x=get(gcbo,'Value');
switch x
    case 1
        set(neededHandler,'String',string1);%I want to change the contents of the secod popup using the 1st one;
    case 2
        set(set(neededHandler,'String',string2);
        ...
    
end
end

I get an error saying that neededHandler cannot be found,ineed it does no appear in the workspace.I know that functions use some sort of 'private' workspace but I don't know how to acces them.

Answer 1

[Divyajyoti Nayak]

Hi @Adrian Nicolae Culic,

I see that you’re trying to pass a ‘uicontrol’ object handle as an argument to a callback function but you’re getting an error saying the handle cannot be found. This is because the callback function is being created before the ‘neededHandler’ object is being defined, hence MATLAB is not able to find the handle. Defining the callback function after the ‘neededHandler’ object should resolve the error. I edited your code to show the solution:

clear;
clc;
func1();
function func1()
figure('Name','notRelevant',...
    'Units','normalized',...
    'Position',[0.1 0.2 0.7 0.6],...
    'NumberTitle','off','color','#B2BABB');
    Rgr = uipanel;
    popup = uicontrol('Style','popupMenu',...
    'Units','normalized',...
    'Position',[0.26 0.48 0.1 0.15],...
    'String',"Some String",...
    'Value',1,...,
    'Tag','d',...
    'Parent',Rgr);%I have the buttons in an ui panel

    neededHandler=uicontrol('Style','PopupMenu',...
    'Units','normalized',...
    'Position',[0.26 0.68 0.1 0.15],...
    'String','string1',...
    'Value',1,...,
    'Tag','d',...
    'Callback','',...
    'Parent',Rgr);

    popup.Callback = {@func2,neededHandler};
end

Another issue I see in the code is in the arguments of the callback function. When a callback function is called, MATLAB automatically passes two arguments (‘source’ and ‘event’) to it. Therefore to use a function as a callback function, the first two arguments should be reserved for these. Here’s the documentation for it:

https://www.mathworks.com/help/releases/R2020b/matlab/creating_plots/callback-definition.html?searchHighlight=callback%20function&s_tid=doc_srchtitle

Here’s how the callback function should look like:

function func2(~,~,neededHandler)
x=2;
switch x
    case 1
        set(neededHandler,'String',"string1");%I want to change the contents of the secod popup using the 1st one;
    case 2
        set(set(neededHandler,'String','string2'));
     
end
end

Hope this helps!