The label on the button should reflect what the button does, that is, it should describe the change that the button makes.
For example, if you have a call registration system, the button should say “Close call” and the user can click it to close the call. The button should not have the label “Call is Open”, and the user clicks to change the status of the call as very intuitive, since the button effectively does the opposite of what it says on it.
In my opinion, the shortcut - and therefore the function - of a button should rarely, if ever, change. The button is supposed to look like a physical button, and usually they only do one thing. (There are a few exceptions, such as play-pause on the media player, where it is normal to change the icon / button icon, but at least it is copying the button from a real physical device.)
, , : "Open Call" "Close Call" , . , .
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