MATLAB: Input Arguments for Callback Function in a listener

addlistenerevent.eventdatamatlab gui

I am trying to use a listener to update one GUI when the data in another GUI changes. I think I got the listener defined, at least I can see that it has been added to the handle structure, but I dont understand what I should set the inputs to the callback function to. From the documentation I can see that that inputs must be a object handle and event.EventData object but I'm not quite sure what that refers to.

%Get GUI_1 data
gui1_handle = findobj('tag','GUI1');
gui1_data = guidata(gui1_handle);
% Add listener to GUI_2 with trigger from GUI_1
handles.listener=addlistener(gui1_data.pitch1,'Value','PostSet',@updategui2);
% Update handles structure
guidata(hObject, handles);
function updategui2(?????,??????)
gui1_handle = findobj('tag','GUI1');
gui1_data = guidata(gui1_handle);
x=num2str(guidata(gui1_data.pitch1))
set(handles.text3,'string',x);

Thank you for your help

Best Answer

If you do not need to use those inputs, then define your function using input placeholders:

 function updategui2(~,~)

https://www.mathworks.com/help/matlab/matlab_prog/ignore-function-inputs.html

FYI, the object handle is quite useful if you want to know the value or status of the calling object, e.g. what value a button or text box has.

Related Solutions

MATLAB: How to update guidata in the addlistener callback function

Note:

for i = 1:10
   checkbox(i-1) = ...

will error on the first iteration, since checkbox(1-1=0) is not a valid index.

Note 2:

@(hObject, eventdata, handles) callback(hObject, eventdata, handles)

Since this anonymous function only job is to pass all its inputs to another function unchanged, it could just be skipped. That is

@callback

would do the same.

Note 3:

function handle = callback(...)

A proper callback never returns anything since there is no mechanism for getting that return value.

Now for your question, the immediate problem comes from the anonymous function you've defined. An listener callback must have two inputs arguments and only two. These are, the object generating the event, and some event data. Therefore, the inputs to your anonymous function can only be:

@(hobject, eventdata) ...

handles cannot be an input since it won't be sent by the event. Now, if you wanted handles to be passed to your callback function, you could define your anonymous function as:

@(hobject, eventdata) callback(hobject, eventdata, handle)

This would work with you example, but I wouldn't recommend that. The anonymous function captures the content of the handle structure at the point it is defined, so any change to that handle structure after that line won't be seen by your callback, e.g.:

lh = addlistener(handles.checkboxes, 'Value', 'PostSet', @(hObject, eventdata) callback(hObject, eventdata, handles));
handles.text = uicontrol('Style', 'text', 'String', 'some new control');  %add a new control to handle

The handle received by your callback will not contain the text field as it was created after handle was captured.

A safer way is simply to get the handle structure with guidata inside your callback, so:

lh = addlistener(handles.checkboxes, 'Value', 'PostSet', @callback);  %not passing handle to callback
function callback(hObject, eventdata) %not receiving handle
   handle = guidata(hobject);   %get handle inside the callback. 
   %...

MATLAB: Image file transfer from one GUI to another using setappdata and getappdata

Rupam - there are probably several different ways to do this, so here is one. Let's assume that you have two GUIs named Gui1 and Gui2 and that they are distinct GUIs (i.e. you are not running two instances of the same one). In the Property Inspector for Gui1, set the HandleVisibility property to on, and the Tag property to Gui1. This will allow us to search for the GUI given its (unique) tag. Do the same for Gui2 (except name the tag Gui2). Save both.

Now suppose that in Gui2 you want access to some of the data in Gui1. What you require, is the handle to the latter. In a (say) push button callback of Gui2, you can add the following code

 function pushbutton1_Callback(hObject, eventdata, handles)
 % get the handle of Gui1
 h = findobj('Tag','Gui1');
 % if exists (not empty)
 if ~isempty(h)
    % get handles and other user-defined data associated to Gui1
    g1data = guidata(h);
    % maybe you want to set the text in Gui2 with that from Gui1
    set(handles.text1,'String',get(g1data.edit1,'String'));
    % maybe you want to get some data that was saved to the Gui1 app
    x = getappdata(h,'x');
 end

The above example tests out two ways in which we can get data from the other GUI - use either guidata which gives us the handles to all widgets of Gui1 AND any user-defined data that had been saved in Gui1 to the handles object as

 function pushbutton3_Callback(hObject, eventdata, handles)
 % in some Gui1 callback, we create the following xData field in the handles

 % structure

 handles.xData = -2*pi:0.0001:2*pi;
 % now we save the data

 guidata(hObject,handles);

We then access this data as shown previously.

The other way is to use the setappdata and getappdata pairings. Using the previous callback for Gui1, we can save the app data as

 function pushbutton3_Callback(hObject, eventdata, handles)
 % in some Gui1 callback, we create the following xData field in the handles
 % structure
 handles.xData = -2*pi:0.0001:2*pi;
 % now we save the data
 guidata(hObject,handles);
 setappdata(handles.Gui1,'x',[1:53]);

and then retrieve it with getappdata.

NOTE how we use must use the handles.Gui1 to save/set the data. And that is it. Try the above and see what happens!

Best Answer

Related Solutions

MATLAB: How to update guidata in the addlistener callback function

MATLAB: Image file transfer from one GUI to another using setappdata and getappdata

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