When a tag is defined for an app designer slider, the value-changing-function for that slider is not triggered.

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Sherman Marcus 2024-10-7

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https://ww2.mathworks.cn/matlabcentral/answers/2157825-when-a-tag-is-defined-for-an-app-designer-slider-the-value-changing-function-for-that-slider-is-not

评论： Sherman Marcus 2024-10-8

I'm using Version R2024a. When I create a slider component in App Designer and define a ValueChangingFcn for it, it works fine ... as long as "Tag" (in the "Identifiers" section of the slider) has not been defined. That is, the ValueChangingFcn callback is called as I drag the slider. However, if I define Tag (e.g. 'abc' without the quotes), then the ValueChangingFcn is no longer called when I drag the slider.

I should mention that this appears to occur only with the slider. With a Numeric Edit Field, the presence of a tag has no adverse effect on the call to its callback.

Does anyone know a workaround?

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dpb 2024-10-7

Have you checked for any updates for your installation? Which OS and updates for it? Added any new apps to the system?

Does the symptom appear for all sliders or only one?

Does the existing slider then trigger if you clear the 'Tag' property?

Does the problem reoccur if you delete the slider(s) and recreate them?

If the symptom does not go away if you delete all sliders and recreate them and since you note it did not appear in a new app, it would appear something has corrupted the particular project and you may have no recourse but to recreate it unless you have an earlier save version from before the time the symptom appeared that you can use as a starting point.

If it doesn't go away and you can't recreate, the only alternatives I see would be to

Don't use the 'tag' property on the affected slider(s), or
Use 'UserData' in lieu of 'Tag', presuming that also doesn't cause the symptom

I would also suggest you could attach the .mlapp file to the forum and others could then see if the symptom is reproducible on other installations.

If none of the above resolve the issue, then submit an official support request...

dpb 2024-10-8

编辑：dpb 2024-10-8

That is interesting observation and indeed undoubtedly there's something related somehow; those symptoms would seem to imply the conversion still leaves links to older code left over from GUIDE days despite all the visible user source code being in the new app designer interface.

I would think this would be of interest to Mathworks; I wonder if it is intended or an artifact of the translation that isn't doing what is expected. Or, maybe there's stuff buried so deep behind the scenes it simply isn't possible for the conversion app to be able to fix.

Does your UI rely on the 'Changing' callback to do something different than from the 'Changed' callback?

Sherman Marcus 2024-10-8

My UI definitely takes advantage of 'changing' rather than 'changed'. When 'changing', I can show the effects while moving the pointer, thereby providing ongoing insight into the various physical phenomena. As a matter of fact, even in GUIDE, I recall I used some "listener" function to provide that same 'changing' effect.

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When a tag is defined for an app designer slider, the value-changing-function for that slider is not triggered.

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When a tag is defined for an app designer slider, the value-changing-function for that slider is not triggered.

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