将时间戳转换为日期而没有时间的抖动省道错误

Question

我把饭菜和日期存储在Cloud_Firestore中，没有时间。把它拿回来会增加时间。现在我要移除时间以便只留下日期。

我尝试了下面显示的代码，我得到了错误。从dart和cloud_firestore文档中，我找不到将其更改为time的公共方法。formatter.format（现在）错误称为：

我试过这个解决方案

String now The argument type 'String' can't be assigned to the parameter type 'DateTime'.

════════ Exception caught by widgets library ═══════════════════════════════════
Class 'Timestamp' has no instance method 'now'.
Receiver: Instance of 'Timestamp'
Tried calling: now()
The relevant error-causing widget was
    StreamBuilder<QuerySnapshot>

import 'package:flutter/material.dart';
import 'package:mealapp/models/Widgets/whenAndWhatToEat.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:intl/intl.dart';
import 'package:mealapp/models/global.dart';

class MealTile extends StatefulWidget {
  final MealsAndWhen mealsAndWhen;
  MealTile ({ this.mealsAndWhen });

  @override
  MealTileState createState() {
    return MealTileState();
  }
}
class MealTileState extends State<MealTile> {
  String id;
  final db = Firestore.instance;
  String meal;


  Widget buildItem(DocumentSnapshot doc) {
   var now = '${doc.data['Date'].toDate()}';
   var formatter = new DateFormat('dd-MM-yyyy');
    String formatted = formatter.format(now);
    print (formatted);
    return Container(
        margin: const EdgeInsets.all(8.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            Text(
              'Meal: ${doc.data['Meal']}',
              style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold, color: Colors.white),
              textAlign: TextAlign.center,
            ),
            Text(
              'Date: ${doc.data['Date']}',
              style: TextStyle(fontSize: 20, fontWeight: FontWeight.bold, color: Colors.white),
              textAlign: TextAlign.center,
            ),
            SizedBox(height: 12),
            Row(
              mainAxisAlignment: MainAxisAlignment.end,
              children: <Widget>[
                SizedBox(width: 8),
                FlatButton(
                  onPressed: () => deleteData(doc),
                  child: Text('Delete',
                  style: TextStyle(fontWeight: FontWeight.bold,
                  color: Colors.white)
                  ),
                ),
              ],
            ),
          ],
        ),
        decoration: BoxDecoration(
          color: lightBlueColor,
          borderRadius: BorderRadius.all(Radius.circular(12)),
        ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: darkGreyColor,
      body: ListView(
        padding: EdgeInsets.only(top: 220),
        children: <Widget>[
          StreamBuilder<QuerySnapshot>(
            stream: db.collection('mealList').snapshots(),
            builder: (context, snapshot) {
              if (snapshot.hasData) {
                return Column(children: snapshot.data.documents.map((doc) => buildItem(doc)).toList());
              } else {
                return SizedBox();
              }
            },
          )
        ],
      ),
    );
  }

  void deleteData(DocumentSnapshot doc) async {
    await db.collection('mealList').document(doc.documentID).delete();
    setState(() => id = null);
  }
}

Answer 1

当在引号内使用DateTime时，您将它转换为字符串，并且在编译时不会出错，因为您将它分配给var，而不是DateTime。在大多数情况下，避免使用var，并明确变量的类型；

DateTime now = doc.data['Date'].toDate();
DateFormat formatter = DateFormat('dd-MM-yyyy');
String formatted = formatter.format(now);