Q:

Get data cursor callback in Matlab GUI

How can I set the Matlab GUI data cursor callback for a specific GUI axes?
I was able to add the data cursor icon in GUI toolbar. I can selected 3D point on the plotted data, but I need to add more info in the data cursor text and also do some other stuff with the coordinates it is getting.     
I tried to follow "How to add additional info to the data cursor?", but doesn't work for GUI.
GUI axes are not figures, so I'm getting this error:
Error using datacursormode (line 149)
Invalid figure handle
I need the same here, but for GUI axes (figures?):
function test_main
% Plots graph and sets up a custom data tip update function
fig = figure('DeleteFcn','doc datacursormode');
X = 0:60;
t = (X)*0.02;
Y = sin(-16*t);
plot(X,Y)
dcm_obj = datacursormode(fig); % tried here "handles.MyFigHandle"
set(dcm_obj,'UpdateFcn',{@myupdatefcn,t})

function txt = myupdatefcn(~,event_obj,t)
% Customizes text of data tips
pos = get(event_obj,'Position');
I = get(event_obj, 'DataIndex');
txt = {['X: ',num2str(pos(1))],...
       ['Y: ',num2str(pos(2))],...
       ['I: ',num2str(I)],...
       ['T: ',num2str(t(I))]};

For now I can get only the default datacursor behavior, like this image:

A:

I've not found any difference between the use of the data cursor in a GUI and in a figure.
Re-using part of your code, I've created a GUI in which a checkbox enable / disable the datacursormode.
The GUI contains two axes in which two lines and a 3D surface are plotted respectively.
Also three radiobuttons control the string that will be printed in the textbox generated when the datacursormode is enabled.
The tags of the GUI are the folowing:

left axes: axes_2d
right axes: axes_3d
left pushbutton: pushbutton_2d
right pushbutton: pushbutton_3d
checkbox: checkbox_enable_dc
left radiobutton: radiobutton1
middle radiobutton: radiobutton2
righ radiobutton: radiobutton3

The GUI works this way:

the pushbuttons plot in the axes and enable the checkbox
the checkbox enable / disable the datacursormode
by default, the left radiobutton is selected and sets the default string
the other two radiobutton set a different string

Based on the selected radiobutton, the first line of the string in the textbox will be either:

DEFAULT STRING
STRING OPTION ONE
STRING OPTION TWO

the string to be written in the textbox is created in your myupdatefcn that has been modified to handle the options selected by the radiobutton.
Notice: in order not to limit the modification to your version of the myupdatefcn function, I've hard coded the t array.
This is the .m file of the GUI:
function varargout = gui_datacursormode(varargin)
% GUI_DATACURSORMODE MATLAB code for gui_datacursormode.fig
%      GUI_DATACURSORMODE, by itself, creates a new GUI_DATACURSORMODE or raises the existing
%      singleton*.
%
%      H = GUI_DATACURSORMODE returns the handle to a new GUI_DATACURSORMODE or the handle to
%      the existing singleton*.
%
%      GUI_DATACURSORMODE('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in GUI_DATACURSORMODE.M with the given input arguments.
%
%      GUI_DATACURSORMODE('Property','Value',...) creates a new GUI_DATACURSORMODE or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before gui_datacursormode_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to gui_datacursormode_OpeningFcn via varargin.
%
%      *See GUI Options on GUIDE's Tools menu.  Choose "GUI allows only one
%      instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES

% Edit the above text to modify the response to help gui_datacursormode

% Last Modified by GUIDE v2.5 02-Apr-2017 17:45:45

% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @gui_datacursormode_OpeningFcn, ...
                   'gui_OutputFcn',  @gui_datacursormode_OutputFcn, ...
                   'gui_LayoutFcn',  [] , ...
                   'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end

if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT

% --- Executes just before gui_datacursormode is made visible.
function gui_datacursormode_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% varargin   command line arguments to gui_datacursormode (see VARARGIN)

% Choose default command line output for gui_datacursormode
handles.output = hObject;

% Update handles structure
guidata(hObject, handles);

% UIWAIT makes gui_datacursormode wait for user response (see UIRESUME)
% uiwait(handles.figure1);

% --- Outputs from this function are returned to the command line.
function varargout = gui_datacursormode_OutputFcn(hObject, eventdata, handles) 
% varargout  cell array for returning output args (see VARARGOUT);
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Get default command line output from handles structure
varargout{1} = handles.output;

% --- Executes on button press in pushbutton_2d.
function pushbutton_2d_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton_2d (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Plot two lines in the first axes
t=0:.1:2*pi;
plot(handles.axes_2d,t,sin(t),'r');
hold(handles.axes_2d,'on')
plot(handles.axes_2d,t,cos(t),'b');
% Enable the checkbox that will set datacorsormode on
handles.checkbox_enable_dc.Enable='on';

% --- Executes on button press in pushbutton_3d.
function pushbutton_3d_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton_3d (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Plot a 3D graph in the second axes
axes(handles.axes_3d);
peaks

% Enable the checkbox that will set datacorsormode on
handles.checkbox_enable_dc.Enable='on';

function txt = myupdatefcn(~,event_obj,t)
% Customizes text of data tips

% Get the handles of the GUI to access to the radiobuttons
my_guidata=guidata(gcf);
% Define the additional string to be written
if(my_guidata.radiobutton1.Value)
   str='DEFAULT STRING ';
elseif(my_guidata.radiobutton2.Value)
   str='STRING OPTION ONE ';
else
   str='STRING OPTION TWO ';
end

% Get the datacursor data
pos = get(event_obj,'Position');
I = get(event_obj, 'DataIndex');
% Create the whole string to be written
txt = {[str], ...
       ['X: ',num2str(pos(1))],...
       ['Y: ',num2str(pos(2))],...
       ['I: ',num2str(I)],...
       ['T: ',num2str(t(I))]}

% --- Executes on button press in checkbox_enable_dc.
function checkbox_enable_dc_Callback(hObject, eventdata, handles)
% hObject    handle to checkbox_enable_dc (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% If the checkbox is set
if(hObject.Value)
   %  enable the radiobuttons that control the string to be written
   handles.radiobutton1.Enable='on';
   handles.radiobutton1.Value=1;
   handles.radiobutton2.Enable='on';
   handles.radiobutton3.Enable='on';
   % Create the datacursormode object
   dcm_obj = datacursormode(gcf)
   t=rand(1,10000);
   set(dcm_obj,'DisplayStyle','datatip',...
      'SnapToDataVertex','off','Enable','on', ...
      'UpdateFcn',{@myupdatefcn,t})
else
   % If the checkbox is not set, disable the datacursormode
   datacursormode 'off'
end

% --- Executes on button press in radiobutton1.
function radiobutton1_Callback(hObject, eventdata, handles)
% hObject    handle to radiobutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of radiobutton1

% Toggle the other radiobuttons
handles.radiobutton2.Value=0
handles.radiobutton3.Value=0

% --- Executes on button press in radiobutton1.
function radiobutton2_Callback(hObject, eventdata, handles)
% hObject    handle to radiobutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of radiobutton1

% Toggle the other radiobuttons
handles.radiobutton1.Value=0
handles.radiobutton3.Value=0

% --- Executes on button press in radiobutton1.
function radiobutton3_Callback(hObject, eventdata, handles)
% hObject    handle to radiobutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of radiobutton1

% Toggle the other radiobuttons
handles.radiobutton1.Value=0
handles.radiobutton2.Value=0

Hope this helps,
Qapla'

