ios - Unable to download firebase database to my app -

i new programming in swift. trying make app downloads student data firebase database. unable app running. json file:

{"classa":[ { "name": "student1", "usn": "1ds16cs095" }, { "name": "student2", "usn": "1ds16cs065" }, { "name":"student3", "usn":"1ds16cs047" } ] } 

this code download above json file , put in tableview. modelstudent class have variables name , usn stored. , marksstudentlisttableviewcell class using manipulate labels of prototype cell.

import uikit import firebase import firebasedatabase  struct studentdata { let studentname : string let studentusn : string }  class marksstudentlist: uiviewcontroller, uitableviewdelegate, uitableviewdatasource{  var fetchedstudentids = [studentdata]()  @iboutlet weak var tableview: uitableview! var ref: databasereference! var _selectedsub: int! var selectedsub: int {     {         return _selectedsub     }set {         _selectedsub = newvalue     } }      override func viewdidload() {         tableview.delegate = self         tableview.datasource = self         if(classselected==0){         ref = database.database().reference().child("classa")         ref.observe(dataeventtype.value, with: { (snapshot) in             if snapshot.childrencount>0{                 students in snapshot.children.allobjects as! [datasnapshot]{                     let studentobject = students.value as? [string: string]                     let studentname = studentobject?["name"]                     let studentusn = studentobject?["usn"]                     let student = modelstudent(name: studentname , usn: studentusn)                     self.fetchedstudentids.insert(studentdata(studentname :(studentname as? string!)! , studentusn : (studentusn as? string!)! ) , at: 0)                 }                 self.tableview.reloaddata()             }         })   } }  override func didreceivememorywarning() {     super.didreceivememorywarning()     // dispose of resources can recreated. }  func numberofsections(in tableview: uitableview) -> int {     return 1 } func tableview(_ tableview: uitableview, numberofrowsinsection section: int) -> int {     return fetchedstudentids.count }  func tableview(_ tableview: uitableview, cellforrowat indexpath:  indexpath) -> uitableviewcell {      let cell = tableview.dequeuereusablecell(withidentifier:     "marksstudentlistcell", for: indexpath) as! marksstudentlisttableviewcell      cell.namelbl.text = fetchedstudentids[indexpath.row].studentname//    student name comes firebase     cell.usnlbl.text = fetchedstudentids[indexpath.row].studentusn     return cell }      @ibaction func backbtn(_ sender: any) {     dismiss(animated: true, completion: nil) } } 

using swift struct best way firebase data inside tableview,

let's started

on tableview swift file, above class , stuff paste this

   struct studentdata {    let studentobject : string // if it's    let studentname : string // returns string right?    let studentusn : string                    // others. } 

okay create var down below class call it

var fetchedstudentids = [studentdata]() 

then got reading method firebase

     ref = database.database().reference().child("classa")             ref.observe(dataeventtype.value, with: { (snapshot) in                 if snapshot.childrencount>0{                     self.studentslist.removeall()                     students in snapshot.children.allobjects as! [datasnapshot]{                         let studentobject = students.value as? [string: anyobject]                         let studentname = studentobject?["name"]                         let studentusn = studentobject?["usn"]                         let student = modelstudent(name: studentname as! string?, usn: studentusn as! string?) //storing in modelstudent class                         self.  fetchedstudentids.insert(studentdata(studentname:studentname as! string , studentusn : studentusn as! string  ) , at: 0) // student name comes struct above, others                     }                     self.tableview.reloaddata() // make sure call                 }             }) 

return tableview

    func numberofsections(in tableview: uitableview) -> int {     return 1 } func tableview(_ tableview: uitableview, numberofrowsinsection section: int) -> int {     return fetchedstudentids.count } 

your cellforrowatindexpath

    func tableview(_ tableview: uitableview, cellforrowat indexpath: indexpath) -> uitableviewcell {        let cell = tableview.dequeuereusablecell(withidentifier: "cell", for: indexpath) as! tableviewcell   cell.examplelabel.text = fetchedstudentids[indexpath.row].studentname// student name comes firebase         return cell } 

hope helps