How to select only two items from the list box?

I want to select only two items from a list box. The list box should not accept more than two selected items.

Please provide an example for this.

Answer 1

[Matthew Simoneau]

You can accomplish this by reacting to the selection with a callback and removing the new selection if there are too many.

Create a callback function like this one:

function twoOnly(h,~)

oldValues = get(h,'UserData');
newValues = get(h,'Value');

if numel(newValues) > 2    
    newValues = oldValues;
end

set(h,'Value',newValues)
set(h,'UserData',newValues)

end

Here's an example of how to use it:

close all;
u = uicontrol( ...
    'style','listbox','Max',2,'Position',[10 10 100 100], ...
    'String',{'one','two','three','four','five'}, ...
    'Callback',@twoOnly)

Note that the 'Max' property with a value of "2" has nothing to do with the limit of two selections. For more information, see the uicontrol reference page.

[Joe S]

Works great, tested using both the CTRL and SHIFT button multl-select. Note: If using GUIDE for a GUI, you'll likely need to change "h" to "hObject" and remove "function twoOnly(h,~)"

Answer 2

[Walter Roberson]

There is no (documented) MATLAB mechanism for restricting the number of multi-selected items in a listbox. Your callback function will need to detect the situation and decide what to do, such as setting the Value property to only reflect the first (or last) two of the chosen values, or popping up an error dialog.