How do I declare setState in flutter?

setState method Null safety Notify the framework that the internal state of this object has changed. Whenever you change the internal state of a State object, make the change in a function that you pass to setState: setState(() { _myState = newValue; }); The provided callback is immediately called synchronously.

Read more

Where we can use setState in Flutter?

When you change the state of a Stateful Widget , use setState() to cause a rebuild of the widget and its descendants. You don’t need to call setState() in the constructor or initState() of the widget, because build() will be run afterward anyway. Also don’t call setState() in synchronous code inside build().28 May 2021

Read more