Updates the state of the action. Default implementation does nothing.
Override this method to provide the ability to dynamically change action's
state and(or) presentation depending on the context (For example
when your action state depends on the selection you can check for
selection and change the state accordingly).
This method can be called frequently, and on UI thread.
This means that this method is supposed to work really fast,
no real work should be done at this phase. For example, checking selection in a tree or a list,
is considered valid, but working with a file system or PSI (especially resolve) is not.
If you cannot determine the state of the action fast enough,
you should do it in the
AnAction.actionPerformed(AnActionEvent) method and notify
the user that action cannot be executed if it's the case.
If the action is added to a toolbar, its "update" can be called twice a second, but only if there was
any user activity or a focus transfer. If your action's availability is changed
in absence of any of these events, please call
ActivityTracker.getInstance().inc() to notify
action subsystem to update all toolbar actions when your subsystem's determines that its actions' visibility might be affected.