A test of whether or not your
vm function should run in
response to a State change. For advanced use only.
Some changes to the State of your application will mean your
vm function can't produce a useful Model. In these cases, such as when
performing exit animations on data that has been removed from your Store,
it can be best to ignore the State change while your animation completes.
To ignore a change, provide a function that returns true or false. If the
returned value is false, the change will be ignored.
If you ignore a change, and the framework needs to rebuild the Widget, the
builder function will be called with the latest Model produced
typedef ShouldUpdateModel<St> = bool Function(St state);