Is it possible to use a script as a callback or ButtonDownFcn in uicontrol?

What I am trying to do is add a button to a figure CIW and when that button is pressed I want a script to execute. This seems like a very simple task, but the only way I found it to work is by going through functions. I don't see why i should need to go through a function, but this is the only way I have gotten it to work.

What I am trying to do.. Where displayText is a script with 1 line of code: disp('success')

% Add Proceed Button To Figure
pButton = uicontrol(CIW,'Style','pushbutton','Units','pixels',...
                    'FontName','Tw Cen MT','FontSize',16,...
                    'String','Proceed','Position',[pBpos,Bdim],...
                    'ButtonDownFcn', displayText);

What I found that works

% Add Proceed Button To Figure
pButton = uicontrol(CIW,'Style','pushbutton','Units','pixels',...
                    'FontName','Tw Cen MT','FontSize',16,...
                    'String','Proceed','Position',[pBpos,Bdim],...
                    'Callback', @displayText);

function displayText(src,event)
disp('success')
end

Is there a way to execute a script without going through a function?

Answer 1

[Voss]

% Add Proceed Button To Figure
pButton = uicontrol(CIW,'Style','pushbutton','Units','pixels',...
                    'FontName','Tw Cen MT','FontSize',16,...
                    'String','Proceed','Position',[pBpos,Bdim],...
                    'Callback', 'displayText');

[Voss]

Of course, you'll have to make sure displayText.m is a script and that there's no function called displayText somewhere, e.g., from when you created the function displayText for testing purposes.

[Christopher Headley]

It worked!! Gosh, I could have sworn i tried this. Thanks a lot Voss, you too Jan.

[Voss]

You're welcome!

Maybe it was 'ButtonDownFcn','displayText' when you tried it before.

[Christopher Headley]

That is quite possible. Sticking to Callback from now on!

[Walter Roberson]

Note: When you provide a character vector as a callback, the character vector is executed in the base workspace. Local variables are not available, and neither are nested functions or local functions. That is why you would need displayText.m to exist as a separate file -- because as a separate file is the only way to locate it from the base workspace.

Answer 2

[Jan]

'ButtonDownFcn', @(h,e) run('displayText')

[Christopher Headley]

That didn't work. Nothing runs when I hit the button using that code.

[Voss]

Use Callback instead of ButtonDownFcn. From the documentation:

"The ButtonDownFcn callback is a function that executes when the user clicks a mouse button on a UI component. The callback executes in the following situations:

• The user right-clicks the UI component, and the Enable property is set to 'on'.
• The user right-clicks or left-clicks the UI component, and the Enable property is set to 'off' or 'inactive'."

[Christopher Headley]

even with the enable property set to on, this answer still didn't work.

[Voss]

The ButtonDownFcn executes when you right-click on an enabled uicontrol, or when you click a disabled or inactive uicontrol. So it's not usually what you want.

[Christopher Headley]

Disregard my comments above. The code does work, but as Voss pointed out, you must right click in order for the button to work. Not very intuitive, but the mistake is on my end for reading over the fact that you must right click.

[Jan]

@Christopher Headley: Sorry, using the 'Callback' is the way to go, if you want a reaction to a left click. I've copied the 'ButtonDownFcn' from the original question.

Using CHAR vectors to define a callback is still supported, but deprecated since Matlab 6.5 - 20 years now. The CHAR vector is evaluated in the base worksapce, so if you are using the name of a script, it modifies the variables stored there. You do not have access to the data stored in the GUI.

But you can call a script from inside a function callback:

handles.FigH = figure;
handles.ButtonH = uicontrol('Style', 'Pushbutton', ...
    'Callback', @myCallback);
guidata(handles.FigH, handles);

function myCallback(ButtonH, EventData)
handles = guidata(ButtonH);
yourScript;
end

Now the contents of handles is visible in the script and you could use the results to modify the GUI. But you still have the drawback, that yourScript is still a script only. Using functions instead is more reliable and recommended for productive code.

[Christopher Headley]

Thanks for the advice Jan. I was unaware of the base workspace and how it could affect visibility of variables. Or maybe I am aware of it but don't fully understand what you and Walter are referring to. Either way, after each button click I plan on wiping the figure and repopulating it with different images and callbacks so I believe I'll be okay going the script route.

I get what you are saying though with adding a figure so I could see the data from my script. I'll keep y'all updated if I have any issues with my application

[Walter Roberson]

@Christopher Headley

MATLAB has what it calls "workspaces". Those are more or less independent containers with lists of variables and corresponding values. Each time a variable is to be evaluated, it is looked up within the context of a workspace.

There is the "base" workspace, which is the workspace you access at the command line when you are not stopped inside the debugger inside a function. If you are executing code that involves only scripts (and scripts calling other scripts) with no functions involved, then those are all evaluating inside the "base" workspace. If you are executing inside a function, you can deliberately access the base workspace by using evalin('base') and assignin('base')

There is the "global" workspace of variables that can be deliberately shared. There is no evalin('global') or assignin('global') but if you use the global command you can tell your current workspace that any reference to the given name is to work with the global workspace. global variables are not visible inside of functions unless you specifically use global to access them.

There is a workspace for each function. Inside a function, any variable declared as "persistent" is shared by all invocations of the function, and will continue to exist after the function returns, being available the next time the function is run. Inside a function, any variable not marked as persistent or global will be destroyed when the function returns.

The only user-accessible way for one function to look at the local variables of another function, is the very limited evalin('caller') and assignin('caller') that a function can use to interact with the workspace of the function that called it.

Now, suppose you had code something like

function handles = pushbutton1_init(handles)
    count = handles.count;
    handles.pushbutton1 = uicontrol('style', 'push', 'Callback', 'disp(count)');
end

and suppose that your intention was that every time the pushbutton was called, that the variable count would be displayed. But... as soon as you return from pushbutton1_init, the count that is inside the function workspace for pushbutton1_init would be destroyed. The pushbutton being created will outlive the workspace of the function that creates the uicontrol. If the disp(count) were referring to that variable count then when you pushed the button sometime later it would be trying to display a variable that did not exist.

But in fact when you code a text Callback, the callback is not executed inside the workspace of the function that created the callback: instead the text callback is executed inside the base workspace. The base workspace always exists -- but if the base workspace happens to have a variable count at all then that variable might not happen to have any relationship to the variable you tried to create in pushbutton1_init

What can be done? Well, see http://matlab.wikia.com/wiki/FAQ#How_can_I_share_data_between_callback_functions_in_my_GUI.28s.29.3F . Most of the time, using a text callback is not the best answer. You can use

function handles = pushbutton1_init(handles)
    assignin('base', 'count', handles.count);
    handles.pushbutton1 = uicontrol('style', 'push', 'Callback', 'disp(count)');
end

and that would do something.