I am trying to programmatically create some GUI pushbuttons, but I am unable to retrieve the values passed in the callback. I want to find out the value and string attribute of the button pressed.

 function autobuttongenrate

        f = figure;

        numOfButtons = 7;
        p = uipanel(f,'Title','My Panel',...
             'Position',[0 0 .3 1]);
        buttonHeightPercent = (100/(numOfButtons + (numOfButtons*0.1)))/100;
        unitDistanceBtwButtons = ((100 - (buttonHeightPercent*100*numOfButtons))/(numOfButtons+1))/100;
        bArr =  zeros(1, numOfButtons);
        for n = 1:numOfButtons 
            newButtonButtomMargin = 1 - ((unitDistanceBtwButtons + buttonHeightPercent) * n);
            bnew = uicontrol(p,'Style','pushbutton','String',n,...
                               'Value',n,...
                               'Units','normalized',...
                               'Position',[.1 newButtonButtomMargin .8 buttonHeightPercent],...
                               'Callback', @setmap);
            bArr(n) = bnew;
        end

        ax = axes('Parent',f,'Position',[.4 .25 .5 .5]);

        function setmap(source,event)
            src = source;
            eve = event;
            h = msgbox({'pushbutton pressed'});
        end

 end

Answer 1

[Walter Roberson]

If you are using R2014b or later, you need to replace

bArr =  zeros(1, numOfButtons);

with

bArr = gobjects(1, numOfButtons);

Your callback should be something more like

        function setmap(source,event)
            button_string = get(source, 'String');
            button_value = get(source, 'Value');
            h = msgbox( sprintf('Button with string "%s" now has value %d', button_string, button_value);
        end

If you are using R2014b or later this can be written as

        function setmap(source,event)
            button_string = source.String;
            button_value = source.Value;
            h = msgbox( sprintf('Button with string "%s" now has value %d', button_string, button_value);
        end

Note: The _Value' property of a uicontrol style 'pushbutton' will remain what you originally configured it as, 'Value',n, until the button is pressed. During the Callback that is processed upon the button being pressed, the Value property will have the same number as the Max property, which defaults to 1 -- so during that callback the Value will be 1. Then as soon as that callback finishes, the Value property will be set to the same number as the Min property, which defaults to 0 -- so after the callback the Value will be 0. This 1 (Max) and 0 (Min) applies no matter what Value you originally configured with, so there is probably no point in setting the Value to n originally. If you want the 1 to persist then consider using a 'toggle' instead of a push: toggle switch between Min and Max values each time they are pressed.

Also: if you have reason to look directly at a pushbutton, you might want to consider giving it a Tag, as you can then findobj() on the Tag. On the other hand, it is more efficient to store them in an array and index the array -- you just have to save the array somewhere... such as in the handles structure.

[Abhay Aradhya]

Thank you for that, I will update my Matlab Version and check.

It would be really helpful if you could elaborate more on findobj() and indexed array methods probably with a small peace of code. Thank you in advance.

I am new to MatLab GUI so please excuse.

[Walter Roberson]

Suppose you have multiple figures and you have a button with 'Tag' 'Launch' that might or might not be associated with the "current" figure. Then provided there are no other items with the same Tag,

launch_button = findobj(0, 'tag', 'Launch');
launch_is_currently_pressed = get(launch_button, 'Value')

This involves searching all of the graphics objects that exist.

If you happen to have a handle to the figure it is in, say f, then you can cut down the search with

    launch_button = findobj(f, 'tag', 'Launch');

This does not require any knowledge of the relative order in which you created the objects.

But on the other hand, suppose you do have that handle available to your code, and you do know that it was (say) the 5th button you are interested in. Then after the loop in which you assigned to bArr you might perhaps do

set(f, 'UserData', bArr);

And then when you want to fetch the handle to it,

bArr = get(f, 'UserData');
launch_button = bArr(5);

This does not require any searching, so it can be significantly more efficient.

Here, I stored bArr into a property of f and pulled it out later under the assumption that you will be wanting to retrieve the value within some function or callback that does not have access to the original bArr variable that you stored the information into.

[Abhay Aradhya]

Thanks a lot tried out everything that you suggested. Was a great learn.

I was trying to find out which among the buttons generated is currently pressed. Is there a better way to find out which among the buttons is pressed?

My ultimate aim here would be to have different set of data associated with each button(as an array of objects), and upon the click of a specific button I would like to display the corresponding data on the plot to the right of the pushbuttons.

[Walter Roberson]

You could do that, or you could use a listbox to select which one to plot.

If you have an array of buttons like your bArr then, for example,

set(bArr, 'Callback', @(src, event) fprintf('index was: %d\n', find(bArr == src)) )

[Stephen23]

"is there a better way to find out which among the buttons is pressed?"

A simple anonymous function does the trick:

for n = ...
    bnew = uicontrol(p,...,'Callback', @(h,e)setmap(n)
end

and

function setmap(n)
fprintf('button %d was pressed.\n',n)
end

[Abhay Aradhya]

Thank you Walter and Stephen both the methods worked well. Great leanings.