Blank GUI figure handle? (noob question)

sorry for this noob question, i just started to learn about GUI making, but i cannot figure out this:

when i create a new blank GUI using GUIDE, an .m file is generated. i cannot find inside this .m file the handle of the blank figure. callback functions of all gui elements (e.g. push buttons) are pointing to the same handles "hObject".

 so what is the handle of the blank figure, and what are the handles of added gui elements?

Answer 1

[Jan]

Although it might look confusing, the situation is clear and surely will become clear to you soon. You can create a button programatically or by guide. Both are equivalent, when you write:

handles.myButton1 = uicontrol('Style', 'PushButton', 'Tag', 'myButton1', ...
'Callback', @myButton1Callback);

Now the callback of the button is called as:

function myButton1Callback(hObject, EventData)

And inside this function you can obtain the current version of the handles struct easily:

handles = guidata(hObject);

GUIDE appends the handles struct as 3rd input automatically already, such that you get:

function myButton1Callback(hObject, EventData, handles)

But I'm not sure, if this handles struct is the newest version already (I'm not working with GUIDE), but the guidata method shown above will work also.

Each object in a GUI has its own handles, which can be seen as a pointer or address of the GUI object. In all callbacks, the handle of the activated object is called "hObject", but you can modify the name of the variable freely:

function myButton1Callback(ButtonHandle, EventData)
set(ButtonHandle, 'String', 'I am pressed');

Answer 2

[Vishal Rane]

The hObject is the handle to the object/component triggering the callback. Also the gui/figure handle would be probably in handles.figure. The handles structure contains handles of all the gui components and the gui itself.

[thomas mann]

thank you for your answer, yes, thats true, the handle of the GUI is 'hObject', because if i add set(hObject,'Color',[1,0.4,0.6]) to the .m code, it works! BUT!

if i add 2 buttons via GUIDE, it creates 2 callback functions inside .m file:

function pushbutton1_Callback(hObject, eventdata, handles) and function pushbutton2_Callback(hObject, eventdata, handles)

and both callbacks have the same handles 'hObject'. so if i want to change backgoundcolor of button nr. 2 by pressing button nr. 1, i put

set(hObject,'BackgroundColor',[1,0.4,0.6])

under callback of button nr.1. This changes bckcolor of button nr.1 , not nr.2! i want to point to handle of button nr.2. like

set(handles.pushbutton2,'BackgroundColor',[1,0.4,0.6]) which actually works

but the problem is, if i add a pushbutton via GUIDE, it places only a callback to .m file , but it does not add a button with handle like

handleofpushbutton2 = uicontrol

so i cannot modify handle handles.pushbutton2 to my own when its added to gui.

Answer 3

[Image Analyst]

In GUIDE, double click on the figure to bring up the property inspector. Look at the "Tag" property - that is the handle name of the figure. For example, if the tag is figMainWindow, then in your code you use handles.figMainWindow whenever you need to refer to the main window (GUI) that contains all of your other controls (listboxes, radio buttons, etc.). If you add a push button with the tag "Go", then you will refer to handles.Go.

See the tutorial: http://blogs.mathworks.com/videos/category/gui-or-guide/

[thomas mann]

thank you for your answer, yes, handles.objectTag is the handle, but it is possible to modify from the code the handle, when the uicontorl is added to the gui? like this:

andleofpushbutton2 = uicontrol

please see my answer above for Vishal Rane

Answer 4

[thomas mann]

let me clear up the things:

the reason im confused is, when i add an uicontrol by coding to the .m file, i can explicitly specify the handle of that button like this

myhandle = uicontrol

and then calling back to a function when clicked:

function callback(myhandle,...)

BUT when i place a button via GUIDE, there is no 'myhandle = uicontorl' added to .m file, so i cannot change the handle from the .m file. The handle is already given as handles.tagofthebutton and the callback as function tagofthebutton_callback(hObject,...)

where hObject does NOT specify the handle of a given or different button, but always points to itself. am i right?

[Jan]

Please do not post clarifications in the answers section. If new information are helpful to understand the question, they should appear inside the question, e.g. marked by "[EDITED]" to show readers, that a addition has been inserted.