触发了Flutter FutureBuilder返回空值错误

Question

我试图从Firestore数据库中的给定文档返回一个注释和文章字段。我利用future builder通过listtile返回这些数据。

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

class PostGetter extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
// TODO: implement build
return new Scaffold(
  body: new Container(
    child: new FutureBuilder(
        future: Firestore.instance
            .collection('post')
            .where('article', isEqualTo: 'lpquVtoRNsu0vBLjNByS')
            .getDocuments(),
        builder: (BuildContext context, AsyncSnapshot snapshot) {
          if (snapshot.hasData) {
            if (snapshot.data != null) {
              return new Column(
                children: <Widget>[
                  new Expanded(
                    child: new ListView(
                      children: snapshot.data.documents
                          .map<Widget>((DocumentSnapshot document) {
                        return new ListTile(
                          title: new Text(document['comment']),
                          subtitle: new Text(document['author']),
                        );
                      }).toList(),
                    ),
                  ),
                ],
              );
            } else {
              return new CircularProgressIndicator();
            }
          }
        }),),
);
  }
}

为什么循环进度指示器不能满足返回小部件的需要？

谢谢你的帮助。

Answer 1

试试这个：

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

class PostGetter extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
// TODO: implement build
return new Scaffold(
  body: new Container(
    child: new FutureBuilder(
        future: Firestore.instance
            .collection('post')
            .where('article', isEqualTo: 'lpquVtoRNsu0vBLjNByS')
            .getDocuments(),
        builder: (BuildContext context, AsyncSnapshot snapshot) {
          if (snapshot.hasData) {
            if (snapshot.data != null) {
              return new Column(
                children: <Widget>[
                  new Expanded(
                    child: new ListView(
                      children: snapshot.data.documents
                          .map<Widget>((DocumentSnapshot document) {
                        return new ListTile(
                          title: new Text(document['comment']),
                          subtitle: new Text(document['author']),
                        );
                      }).toList(),
                    ),
                  ),
                ],
              );
            } 
          }else {
              return new CircularProgressIndicator();
            }
        }),),
);
  }
}

否则应该在snapshot.hasdata上，而不是在snapshot.data上！=null