Flutter The error I received when firebase listing

Question

I've been investigating a problem for days. This is how I use Firebase Database. My goal is to list the contents of the firebase database. but every time I try, I get an error.

-urunler
  -elyapimi
    --LB445dadwSDA5
       ad: "deneme"
       fiyat: "110"
       imageurl: "https://firebasestorage.googleapis.com/v0/b/ben..."
       infiyat: "85.55"
    --LbVuRaL2eslQ4deD-C7
       ad: "deneme"
       fiyat: "110"
       imageurl: "https://firebasestorage.googleapis.com/v0/b/ben..."
       infiyat: "85.55"

I want to list the contents of the database. but I get this error.

E/flutter ( 9624): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled 
Exception: type 'double' is not a subtype of type 'String'
E/OpenGLRenderer( 9624): SFEffectCache:clear(), mSize = 0
W/ManagedEGLContext( 9624): doTerminate failed: EGL count is 2 but 
managed count is 1

these are the codes I use

import 'package:denemeflutter/database.dart';
import 'package:firebase_database/firebase_database.dart';
import 'package:flutter/material.dart';

class YenilenCicek extends StatefulWidget{
 @override
State<StatefulWidget> createState() => YenilenCicekState();

 }

class YenilenCicekState extends State  with TickerProviderStateMixin{
static const EndColor = Color.fromARGB(255, 150, 202, 230);
static const StartColor = Color.fromARGB(255, 64, 222, 194);
static const softmavi = Color.fromARGB(255, 142, 226, 210);
List<MyDatabase> list = [];

  @override
 void initState() {
 super.initState();
 DatabaseReference postRef = 
FirebaseDatabase.instance.reference().child("urunler").child("elyapimi");

  postRef.once().then((DataSnapshot snap)
  {
   var keys = snap.value.keys;
   var data = snap.value;

    list.clear();

     for(var key in keys)
     {

       MyDatabase myDatabase = new MyDatabase
         (

         data[key]["ad"],
         data[key]["imageurl"],
         data[key]["infiyat"],
         data[key]["fiyat"]);
     list.add(myDatabase);
   }

   setState(() {
     print("Lenght : $list.lenght");
   });
  });

   }

  @override
 Widget build(BuildContext context) {
  return Scaffold(
  body: Stack(
    children: <Widget>[
      Container(
        height: 100,
        width: double.maxFinite,
        color: Colors.white,
      ),
      Positioned(
        child:Container(
          padding: EdgeInsets.only(left: 170, top: 30),
          height: 100.0,
          decoration: BoxDecoration(
            gradient: new LinearGradient(colors: [StartColor,EndColor]),
            borderRadius: BorderRadius.only(bottomLeft: 
    Radius.elliptical(300, 10) , bottomRight: Radius.elliptical(300, 10) 
  ) ,
          ),
          child: null,
        ),
      ),

      Positioned(
        child: Container(
          padding: EdgeInsets.only(top: 35, left: 0),
          child: FlatButton(
              padding: EdgeInsets.only(left: 0,right: 25),
              onPressed: (){Navigator.pop(context);},
              child: Icon(Icons.keyboard_arrow_left,color: 
      Colors.white,size: 50,)
          ),
        ),
      ),
      Positioned(
          child: Container(
            alignment: Alignment.center,
            margin: EdgeInsets.only(bottom: 525),
            child: Text("YENİLEN ÇİÇEKLER", style: TextStyle(color: 
     Colors.white, fontSize: 19),),
          )
      ),
      Container(
        margin: EdgeInsets.only(top: 130),
        child: list.length == 0 ?  new Text("Bu Kategoride\nÜrün 
      Bulunmamaktadır.", textAlign: TextAlign.center,) : new 
    ListView.builder(

          itemCount: list.length,
          itemBuilder: (_,index){
            return ListUI(list[index].title, list[index].imageurl, 
           list[index].promoprice, list[index].price);
          },

        ),
      )
    ],
  ),
 );
}

 Widget ListUI(String ad,String imageurl,String infiyat,String fiyat,)
{
 return new Card(
  elevation: 10.0,
  margin: EdgeInsets.all(15.0),
  child: new Container(
    padding: new EdgeInsets.all(14.0),
    child: new Row(
      mainAxisAlignment: MainAxisAlignment.spaceBetween,
      children: <Widget>[
        Container(
          child: Image.network("$imageurl"),
        ),
        Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
          Text("$ad", style: TextStyle(color: Color.fromARGB(255, 64, 
       222, 194), fontSize: 18, ),textAlign: TextAlign.center,),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: <Widget>[
                Text("$infiyat", style: TextStyle(color: 
       Color.fromARGB(255, 64, 222, 194), fontSize: 18),),
                Text("$fiyat", style: TextStyle(color: 
        Color.fromARGB(255, 64, 222, 194), fontSize: 18),),
              ],
            )
          ],
        ),
      ],
    ),
   ),
  );
  }
 }

I Thanks in advance to friends who can help.

Solution

In your MyDatabase class, you have infiyat as type String, but it is comming in as a double i.e "85.55". Either change the type in your database or your class.