Question

我有下面的代码，它向我发出如下警告，并在运行时显示 build函数返回null。

此函数的返回类型为“窗口小部件”，但不以return语句结尾。尝试添加return语句，或将返回类型更改为'void'。

更新：下面的代码有什么问题？..

import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:io';
import 'package:path/path.dart';

import 'package:permission_handler/permission_handler.dart';

List<FileSystemEntity> _pdf = [];

class BrowserScaffold extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return TabsApp();
  }
}

Future<List> loadfiles() async {
  _pdf = [];
  int filecount = 0;
  var status = await Permission.storage.status;
  if (status.isUndetermined) {
    await [
      Permission.storage,
    ].request();
  }
  Directory dir = Directory('/storage/emulated/0/');
  String pdfpath = dir.toString();
  print('PATH IS ' + pdfpath);
  List<FileSystemEntity> _files;
  _files = dir.listSync(recursive: true, followLinks: false);
  for (FileSystemEntity entity in _files) {
    String path = entity.path;
    if (path.endsWith('.pdf')) _pdf.add(entity);
  }

  for (var i = 0; i < _pdf.length; i++) {
    //print(_pdf[i]);
  }
  filecount = _pdf.length;
  print('#############ENTERED');
  print(filecount);
  return _pdf;
}

class TabsApp extends State<BrowserScaffold> {


  @override
  Widget build(BuildContext context) {
    return Container(
      child: DefaultTabController(
        length: 2,
        child: Scaffold(
          appBar: AppBar(
            title: Text('MY Files'),
            bottom: TabBar(tabs: [
              Tab(text: 'ALL FILES'),
              Tab(text: 'RECENT FILES'),
            ]),
          ),
          body: TabBarView(
            children: [
              RaisedButton(
                child: Text('LIST FILES'),
                onPressed: () => loadfiles(),
              ),
              FutureBuilder(
                  future: loadfiles(),
                  builder: (context, AsyncSnapshot snapshot) {
                    if (snapshot.hasData) {
                      print('OKOK##################################');
                      if (snapshot.data != null) {
                        return ListView.builder(
                            itemCount: snapshot.data.length,
                            itemBuilder: (context, index) {
                              return Container(
                                  child: Card(
                                child: Text(
                                  basename(snapshot.data[index].path),
                                  style: TextStyle(
                                      fontWeight: FontWeight.bold,
                                      fontSize: 18),
                                ),
                              ));
                              //return Text(snapshot.data[index].path);
                            });
                      } else {
                        print('FAIL##################################');
                        return new CircularProgressIndicator();

                      }
                    } else {
                      print('FAIL2##################################');
                      return Text("Empty");
                    }
                  }),
            ],
          ),
        ),
      ),
    );
  }
}

Answer 1

此函数的返回类型为“小部件”，但不以结束返回声明。尝试添加return语句，或更改将类型返回为“ void”。

警告告诉了您一切。您在那里有两个if，因此您也需要两个else。

if (snapshot.hasData) {
  if (snapshot.data != null) {
    ...
 }else{
    return Text("It is null");
  }
}else{
  return Text("Empty");
}

Flutter FutureBuilder期望返回值

1 个答案: