Answers for "how to fix floating action button on stack flutter"

set floating action button invisible flutter

floatingActionButton: new Visibility( 
        visible: false,
        child: new FloatingActionButton(
          onPressed: _incrementCounter,
          tooltip: 'Increment',
          child: new Icon(Icons.add),
        ),
      ),

flutter floatingactionbutton position

Scaffold(
	floatingActionButton: FloatingActionButton(
        onPressed: () {
          // Add your onPressed code here!
        },
        child: const Icon(Icons.navigation),
      ),
      //BUTTON LOCATION
      floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
);