onWillChange property Null safety

OnWillChangeCallback<St, Model>? onWillChange

A function that will be run on State change, before the Widget is built. This function is passed the Model, and if distinct is true, it will only be called if the Model changes. This can be useful for imperative calls to things like Navigator, TabController, etc


final OnWillChangeCallback<St, Model>? onWillChange;