Question

我想将一个列表从一个类传递到另一个类，我尝试了不同的方式来做，但是列表却返回空，如何将一个类中的列表传递给另一个类？我需要创建具有该列表的PDF文件，但是当我打印它时，我得到的是[]。

我已经尝试过了：

List<String> getProducts() {
    return listaProductos; // This is the list that I'm trying to print in another class, if I call this method in the same class where the method is, I get the filled list, same that I'm trying to pass to another class
}

在我的另一堂课中，我这样做了：

BotanaxState botana2 = new BotanaxState();

List<String> calledList = botana2.getProducts();    

print(calledList);

但是它返回一个空列表。

import 'package:dropdown_list/src/pages/firma.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

/****CLASS ONE****/


class Botanax extends StatefulWidget {
  @override
  BotanaxState createState() => BotanaxState();
}

class BotanaxState extends State<Botanax> {
  final List<String> _dropdownValues = [
    "One",
    "Two",
    "Three",
    "Four",
    "Five"
  ]; //The list of values we want on the dropdown
  String _currentlySelected = ""; //var to hold currently selected value

  List<String> listaProductos = new List<String>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Selected Index - DropdownButton'),
      ),
      //display currently selected item on dropdown
      body: Container(
        alignment: Alignment.center,
        child: ListView(
        //mainAxisAlignment: MainAxisAlignment.start,
        children: <Widget>[
          Text(_currentlySelected),
          SizedBox(
            height: 20.0,
          ),
          DropdownButton(
            //value: _currentlySelected,
            //map each value from the lIst to our dropdownMenuItem widget
            items: _dropdownValues
                .map((value) => DropdownMenuItem(
                      child: Text(value),
                      value: value,
                    ))
                .toList(),
            hint: Text('Selecciona producto'),
            onChanged: (String value) {
              //once dropdown changes, update the state of out currentValue
              setState(() {
                _currentlySelected = value;
                listaProductos.add(_currentlySelected);
              });
            },
            //this wont make dropdown expanded and fill the horizontal space
            isExpanded: false,
          ),
          new Column(
            children: <Widget>[
              SizedBox(
                height: 300,
                child: ListView.builder(
                  itemCount: listaProductos.length,
                  itemBuilder: (BuildContext ctxt, int index) {
                    return new Center(
                      child: (new Center(
                        child: new Text(listaProductos[index]),
                      )),
                    );
                  },
                ),
              ),
              RaisedButton(
                child: Text('Aceptar', style: TextStyle(fontSize: 20)),
                onPressed: () {
                  Navigator.push(
                    context,
                    MaterialPageRoute(
                        builder: (context) => FirmaPage()),
                  );

                  //print(getProducts());
                },
              ),
              /*RaisedButton(
                child: Text('Remove item', style: TextStyle(fontSize: 20)),
                onPressed: () {},
              )*/
            ],
          )
        ],
      )),
    );
  }

  List<String> getProducts()
  {
      return listaProductos;
  }

  /*List<String> MyList
    {
        get { return myList; }
    }*/

    List<String> get productos => listaProductos;
}




/****CLASS TWO****/
import 'package:dropdown_list/src/pages/botanax.dart';
import 'package:flutter/material.dart';

import 'package:pdf/widgets.dart' as pdfLib;
import 'package:open_file/open_file.dart';
import 'package:path_provider/path_provider.dart';
import 'package:pdf/pdf.dart';
import 'dart:io';

class FirmaPDF extends StatefulWidget {
  @override
  _FirmaPDFPageState createState() => new _FirmaPDFPageState();
}

class _FirmaPDFPageState extends State<FirmaPDF> {
  List<String> listaProductos = new List<String>();

  @override
  Widget build(BuildContext context) {
    /*listaProductos.add('odwjef');
    listaProductos.add('34f');
    listaProductos.add('db5');
    listaProductos.add('Wolf');
    listaProductos.add('fv 4f');
    listaProductos.add('Lando');*/


    return new Scaffold(
              body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: <Widget>[
            new RaisedButton(
                child: new Text('Print Document'),
                onPressed: () => generatePdfAndView(context))
          ],
        ),
      ),
      );
  }

  generatePdfAndView(context) async {
    final pdfLib.Document pdf = pdfLib.Document(deflate: zlib.encode);
    final String dir = (await getApplicationDocumentsDirectory()).path;
    final String path = '$dir/ejemplo.pdf';
    final File file = File(path);

    BotanaxState botana2 = new BotanaxState();

    List<String> calledList = botana2.getProducts();    

    print(calledList); //Here I'm getting the empty list
    //print(calledList);
    print(botana2.productos);

    //Botanax drop = new Botanax();
    //print();

    pdf.addPage(pdfLib.Page(
        pageFormat: PdfPageFormat.a4,
        build: (pdfLib.Context context) {
          return pdfLib.Center(
              child: pdfLib.ListView(
                children: <pdfLib.Widget>[
                  pdfLib.Text(calledList.toString()),
                  //pdfLib.Text("Hola"),
                  //pdfLib.Text("Lando"),
                ]
              )
            ); // Center
        }
      )
    );

    file.writeAsBytesSync(pdf.save());
    print(file);
    OpenFile.open(path);
  }

  /*String getTicket(List<String> strings)
  {
    List<String> list = new List<String>();

    for(int i = 0; i < strings.length; i++)
    {
        list.add(strings[i]);
    }

    for (var name in list) 
    {
      list.add(strings[name]);
    }

    return strings.toString();
  }*/
}

第二堂课我需要有相同的清单。

Answer 1

您正在创建new的 BotanaxState 实例，因此它不包含您在另一个实例中存储的数据是有意义的，即您需要访问包含原始实例的变量。

Answer 2

您可以将列表传递给第二堂课。

<table>
  <tr>
    <td>some order things</td>
  </tr>
  <tr>
    <td>some order things</td>
  </tr>
  <!-- ... -->
  <tr t-foreach="o.order_line" t-as="l">
    <td t-field="l.product_id.name" />
    <!-- ... -->
  </tr>
</table>

在第二个类中，在构造函数中声明列表

Navigator.push(
     context,
             MaterialPageRoute(
                         builder: (context) => FirmaPage(listaProductos)),
          );

然后您可以通过以下方式访问它：

class FirmaPDF extends StatefulWidget {
  @override
  _FirmaPDFPageState createState() => new _FirmaPDFPageState();

  FirmaPDF(this.listaProductos)

  List<String> listaProductos;
}

我想将变量从一类传递到另一类

2 个答案: