How to get the value of the variable outside the Future method in Flutter?

Question

I am developing in a book app and am stuck on the screen where will open the file . pdf.

I need to get the path of the mobile directory using path_provider to send to pdfviewer but I can’t get the path in the variable outside the method. However if I give hot realod the path is obtained, but when I return to the screen select book, low, and try to open the path becomes null.

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';
import 'package:flutter_pdf_viewer/flutter_pdf_viewer.dart';

class PdfScreen extends StatefulWidget {

  final DocumentSnapshot document;

  PdfScreen(this.document);

  @override
  _PdfScreenState createState() => _PdfScreenState(document);
}

class _PdfScreenState extends State<PdfScreen> {

  final DocumentSnapshot document;

  _PdfScreenState(this.document);

  dynamic path;

  Future<dynamic> loadPdf() async{

    try{

     var  dir = await getApplicationDocumentsDirectory();

     setState(() {
        path = "${dir.path}/${document["title"]}.pdf";
    }

      return **path**;

    }catch(e){
      print("ERRO: $e");
      return e;
    }
  }

  @override
  Widget build(BuildContext context) {

    loadPdf();
    // path = "/data/data/br.com.apps.d.baixa_livros/app_flutter/${document["title"]}.pdf";
    print(path); // **Aqui printa null**


    return Container();
  }

}

Answer 1

The problem is in the method loadPdf(), do as follows:

Future<void> loadPdf() async {
    try{

        var dir = await getApplicationDocumentsDirectory();

        setState(() {
            path = "${dir.path}/${document["title"]}.pdf";
        }

    }catch(e){
        print("ERRO: $e");
    }
}

The setState() informs for its application that the Widget must be rebuilt, ie, will be executed the block Widget build(BuildContext context) again and its variable path you’ll be fed by then.

Answer 2

It was necessary to use loadPdf() method inside iniState;