Example sort, https://www.facebook.com/groups/1330912973657674/permalink/3112199812195639/

main.dart

class Product{
  String title;
  bool isSale;
  int price;
  Product({this.title,this.isSale,this.price});
  
  toString(){
    return "title = $title, isSale = $isSale, price = $price";
  }
}

void main() {
  List<Product> products = List.generate(30,(i){
    return Product(title: "No.$i",isSale: i %  4 ==0,price: (i * 1000) );
  });
  
  
  products.sort((a,b){
    if((a.isSale && b.isSale) || (!a.isSale && !b.isSale) ){
      if(a.price > b.price){
        return -1;
      }else if(a.price == b.price){
        return 0;
      }else{
        return 1;
      }
    }else if (a.isSale && !b.isSale){
      return -1;
    }
    else{ // !a.isSale && b.isSale
      return 1;
    }
  });
  
 
  
  products.forEach((p){
   print(p.toString());
  });
  
}