selectionChangedFcn repeatedly called after mouse click and key presses

I am using MATLAB 2022b on Windows 10. With the following script and functions, if I left click on the rightmost radio button then press a key twice, the selectionChangedFcn is called endlessly: What did I do wrong?

fig = uifigure( ...
    "WindowKeyPressFcn", @windowKeyPressFcn);

fig.UserData.buttonGroup = uibuttongroup(fig, ...
    'SelectionChangedFcn', @selectionChangedFcn);

width = fig.UserData.buttonGroup.Position(3) / 2;

height = fig.UserData.buttonGroup.Position(4);

fig.UserData.control(1) = uicontrol(fig.UserData.buttonGroup, ...
    'Style', 'radiobutton', ...
    'Position', [1 1 width height]);

fig.UserData.control(2) = uicontrol(fig.UserData.buttonGroup, ...
    'Style', 'radiobutton', ...
    "Position", [(width+1) 1 width height]);

fig.UserData.controlIndex = 1;

function windowKeyPressFcn(source, event)

if source.UserData.controlIndex == 1
    source.UserData.controlIndex = 2;
    source.UserData.control(2).Value = 1;
else
    source.UserData.controlIndex = 1;
    source.UserData.control(1).Value = 1;
end

end % function windowKeyPressFcn

function selectionChangedFcn(source, event)

if event.NewValue.String == "1"
    fprintf("1");
else
    fprintf("2");
end

end % function selectionChangedFcn

Answer 1

[T.Nikhil kumar]

Hello Roberto,

According to the code, you have created a figure with two radio buttons inside a button group. When a user presses any key, the ‘windowKeyPressFcn’ is called, through which you want to toggle the selection between the two radio buttons. You are trying to achieve this by setting the ‘Value’ property of the radio buttons to 1 (which means selected) or 0 (which means not selected).

I would like to point out to you that programmatically changing the ‘Value’ property of a radio button triggers the callback corresponding to ‘SelectionChangedFcn’ property. If a key is pressed again while the ‘SelectionChangedFcn’ is executing, it can lead to a situation where it is going to be called endlessly.

For resolving this issue, I would recommend you to modify the ‘windowKeyPressFcn’ to check if the ‘Value’ of the radio button is already what it is being set to. If it is, the function should not do anything. This prevents the ‘SelectionChangedFcn’ from being called if the radio button is already in the desired state. Please look at the below code snippet for the new ‘windowKeyPressFcn’:

function windowKeyPressFcn(source, event)
    if source.UserData.controlIndex == 1
        if source.UserData.control(2).Value == 0 % Only change if not already selected
            source.UserData.controlIndex = 2;
            source.UserData.control(2).Value = 1;
        end
    else
        if source.UserData.control(1).Value == 0 % Only change if not already selected
            source.UserData.controlIndex = 1;
            source.UserData.control(1).Value = 1;
        end
    end
end % function windowKeyPressFcn

Additionally, I assume that you intend for the ‘selectionChangedFcn’ to print "1" or "2" based on which radio button was selected. For this, I would suggest you modify ‘selectionChangedFcn’ to use ‘Tag’ property of the radio buttons to differentiate between them. Refer to the following code snippet for the modified ‘selectionChangedFcn’:

function selectionChangedFcn(source, event)
    fprintf("%s", event.NewValue.Tag);
end % function selectionChangedFcn

Note that, the ‘Tag’ property is a user-defined identifier for UI components. This requires setting it’s value for each radio button as shown below, prior to usage:

fig.UserData.control(1).Tag = '1';
fig.UserData.control(2).Tag = '2';

Hope this helps you proceed further!

[Roberto Marino]

Hello, T.Nikhil Kumar, and thank you for your response. I tried the changes which you suggested, and they prevent the endless cycle on the left mouse click on the rightmost radio button followed by two key presses. However, the problem recurred when I clicked on the leftmost radio button followed by a single key press.