(App Designer) ListBox Callback - does my value need to change to get a callback?

Hi all,

I have a ValueChangedFnc (Value changed function) for my listbox that correctly responds when I select a different item in my list. I would like the same callback to occur when I click the currently selected item (the value does not change but I would like to repeat the callback).

Is there any other way to add callbacks to the listbox? or do I need to de-select the current item in order to repeat it?

Thanks!

HG

[Geoff Hayes]

Hannah - for the ValueChangedFnc callback, I suspect that the value (selected item) would need to change in order for the callback to fire. Why would you like to re-select the the already selected item? What would be the purpose of doing that?

[Hannah Gillespie]

Hi Geoff,

I basically have two listboxes, one contains x axis information and one contains y axis information. When I select any item in the y axis information box, my gui plots it with respect to whatever is selected in the x axis information box. Now I want to be able to compare the plots with other conditions, so I want to plot the same y axis information with different data sets uploaded. However, my y axis selection is not deselected and I cannot plot the same y data again without first selecting something different. Thanks!

[Marcus Adkins]

Yes, this is a real pain. I initially populate the listbox from an input file (i.e. the items are not set until a file is loaded). I would like to select the listbox item and have it deconstruct the menu string to populate other fields which can then be used, modified, etc. This works fine if the initial data file has more than one item, but if there is only one then I'm stuck.

If anyone finds a workaround for this, I would be very interested.

Answer 1

[Guillaume]

It sounds like you need to change your design slightly. At the moment, it sounds like you're only plotting when y changes but actually you also want to plot when some other information changes. So, extract the plotting code in its own function and call that plotting function from the callback of each relevant control (x, y, etc.)

[Hannah Gillespie]

For further context, I am taking old code from GUIDE and translating it to App Designer. Unfortunately it appears App Designer has decreased functionality.

In GUIDE, "The callback function listbox1_callback executes when the user clicks a list box item."

In App Designer, the ValueChangedFnc "executes when the user selects a different item in the list box."

My question is simply how can I incorporate the GUIDE callback function to execute when the user clicks a list box item, not the App Designer callback that requires the value to actually change.

Thanks!

[Guillaume]

In this instance, I wouldn't say that the App designer has reduced functionality, I'd say it has a much saner design.

As the name indicates, ValueChangedFnc only fires when the values changes. You could possibly detect "when the user clicks a list box item" by catching the WindowButtonDown event of the app but your app would only work properly for mouse users. Keyboard users would be left out.

In any case, that wouldn't be very good design. As I said, if you want something to change in response to any of several things changing, the best course of action is to call that change function from the event handler of each of these things.

If you really need to you can also have a Refresh button.

[Hannah Gillespie]

True, App Designer is much more user friendly!

The WindowButtonDown event actually sounds like exactly what I would need. How do I incorporate that callback in App Designer?

[Guillaume]

Again, I wouldn't recommend using any ***Button*** event as you leave keyboard users (like me) unable to use your GUI. ***Change events can be triggered by keyboard or mouse interactions and are thus more useful.

Furthermore, the WindowButtonDown event of a figure might get intercepted by controls in the figure or might not be triggered on some controls. See the documentation.

As to how incorporate it, the same way you create any other App designer callback. The simplest way is to select the UIFigure in the list of components, go to callbacks and let matlab create the callback function for you.

[Lee]

How can you say this is not reduced functionality? I am experiencing the same problem, whereby after migrating from GUIDE to App Designer, callbacks are no longer firing. I have multiple listboxes, with common action buttons, so it's necessary to know which listbox is currently 'active'. In GUIDE, it was enough to just click inside the Listbox. Now the callback only activates if the value is changed > so what if my listbox sometimes only contains one value? It is now IMPOSSIBLE to 'activate' this listbox. I may be forced to duplicate all my buttons for every listbox unless I find a workaround...

Still think we have the same functionality? objectively NO. Matlab could simply add a kind of SelectionCallback, but there is no option to add any callback other than ValueChanged, thank you Mathworks!

[Marcus Adkins]

OK. Here's an ugly workaround:

When populating my listboxes, I insert a dummy first item with a recognized pattern (space, special character or something). In my callback code, I have a line to ignore that if selected, i.e. the listbox only reacts if one of the other lines are selected. It's not elegant but at least it will allow me never to get 'stuck' by only having one item in the listbox to operate on.

It would be much better if Mathworks simply offered a 'selected' callback for listboxes in addition to the 'value changed' callback which is the only option now.