Why flutter think that my variables are null ?

See more:

Android

HTML5

Dart

Flutter

So I've already had a problem with this code before and got some help to fix my error, but I have a new one. So basically I'm waiting for a variable and this variable is not null because when I print it, I can see the value of this variable. The screen returns the fallback values and I don't know why. I have two screens: one for create my variable and the other for all the graphic stuff.

This is the detail screen:

class DetailScreen extends StatefulWidget {
  const DetailScreen({Key? key, required this.mangaImg, required this.mangaTitle, required this.mangalink}) : super(key: key);
  final String mangaImg,mangaTitle,mangalink;
  @override
  _DetailScreenState createState() => _DetailScreenState();
}

class _DetailScreenState extends State<DetailScreen> {
    String? mangaGenre,mangaStatus,mangaAuthor,mangaDesc;
  List<Map<String,dynamic>>? mangaDetail;
  List<Map<String,dynamic>>? mangaDescList;
  List<Map<String,dynamic>>? mangaChapters;

  Future<void> getMangaInfo() async {
    String  TempBaseurl = widget.mangalink.split(".com")[0] + ".com";
    String TempRoute = widget.mangalink.split(".com")[1];
    final webscraper = WebScraper(TempBaseurl);
    if (await webscraper.loadWebPage(TempRoute)){
     mangaDetail = webscraper.getElement("div.panel-story-info > div.story-info-right > table > tbody > tr > td.table-value", []);
     mangaDescList = webscraper.getElement("div.panel-story-info > div.panel-story-info-description", []);
   }

   mangaGenre  = mangaDetail![3]['title'].toString().trim();
   mangaStatus = mangaDetail![2]['title'].toString().trim();
   mangaAuthor = mangaDetail![1]['title'].toString().trim();
   mangaDesc   = mangaDescList![0]['title'].toString().trim();
   print(mangaDesc);
   print(mangaGenre);
   print(mangaStatus);

  }

    @override

    Future<void> getMangaInfos()async {
    await getMangaInfo();
    }

  @override
  Widget build(BuildContext context) {
    Size screensize = MediaQuery.of(context).size;

    return Scaffold(
      appBar: AppBar(
        backgroundColor: Constants.mygreen,
        title: Text(widget.mangaTitle),
        centerTitle: true,
      ),
      body: Container(
        height: screensize.height,
        width: screensize.width,
        child: SingleChildScrollView(
          child: Column(
            children: [
              MangaInfo(
                mangaImg: widget.mangaImg,
                mangaStatus: mangaStatus??"Error" ,
                mangaAuthor : mangaAuthor??"Error" ,

And this is the graphic screen:

class MangaInfo extends StatelessWidget {
  const MangaInfo({Key? key,  required this.mangaImg,    required this.mangaStatus,   required this.mangaAuthor}) : super(key: key);
  final String mangaImg, mangaStatus,mangaAuthor;

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 300,
      width: double.infinity,

      child: Column(

        children: [
          Expanded(child: Center(child: Column(
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: [
              Container(height: 170, width: 130,child: Image.network(mangaImg, fit: BoxFit.cover,)
              ),
              Text("By $mangaAuthor - $mangaStatus"
                  , style: const TextStyle(
                fontFamily: "SFProDisplay",
              ))
            ],
          ))),
          const SizedBox(
            height: 10,
          ),
          Container(
            height: 80,
            width: double.infinity,
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: const[
                MangaInfoBtn(icon:Icons.play_arrow, title: "Read"),
                MangaInfoBtn(icon:Icons.library_add_check, title: "Favorites"),
                MangaInfoBtn(icon:Icons.list, title: "Chapters"),]

If someone can help me with that I will be really grateful. Thanks!

What I have tried:

At first I change my future into a void, but it was really stupid because it was impossible to await for getMangaInfo()