Passing data to list from json in flutter

Question

I am trying to add data to a list in flutter i have a model class Visitors with a method getVisitors as below

List<Visitor> _visitors=[]

void getVisitors(id, name) {

print(name) //to check if im receiving correct data

var newVisitor=Visitor(id,name);

_visitors.add(newVisitor )

}

My function runs and prints a name on the the debug console but when i run _visitors. Length i get 0 which i don't understand because i thought _visitors.add(newVisitor) would push a mew object to the list

}