使用 Sqflite 时遇到 Flutter 中的错误

Question

import 'package:flutter/material.dart';


import 'package:todoapp/data/data.dart';

import 'package:todoapp/data/task.dart';

class TodoHome extends StatefulWidget {TodoHome({Key? key}) : super(key: key);

  @override
  _TodoHomeState createState() => _TodoHomeState();
}

class _TodoHomeState extends State<TodoHome> {

  Color mainColor= Color(0XFF0d0952);

  Color secondColor=Color(0XFF212061); 

  Color btnColor=Color(0XFFff955b);

  Color editorColor=Color(0XFF4044CC);

  TextEditingController inputcontroller= TextEditingController();
  String newTasktxt='';
  getTasks()async{
   final tasks =await DBProvider.dataBase.getTasks();
   print(tasks);
   return tasks;
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        elevation: 0.0,
        backgroundColor: mainColor,
        title: Text("BMS ToDo",style: TextStyle(
          fontSize: 20.0,
          fontStyle: FontStyle.italic,
        ),),
        centerTitle: true,
      ),
      backgroundColor: mainColor,
      body: Column(
        children: [
          Expanded(child: FutureBuilder(
            future: getTasks  (),
            builder: (_,taskData) {
          
              switch (taskData.connectionState) {
                case ConnectionState.waiting:
                  {
                    return Center(child: CircularProgressIndicator());
                  }
                  case ConnectionState.done:
                  {
                    if (taskData.data != Null) {
                      
                      return Padding(padding: const EdgeInsets.all(9.0),
                    child: ListView.builder(

                      itemCount: taskData.data.length,
                      itemBuilder:( context, index) {
                        String task= taskData.data [index]['task'].toString();
                        String day= DateTime.parse(taskData.data [index]['creationDate']).day
                        .toString();
                        return Card(
                          color: secondColor,
                          child: InkWell(
                            onTap: (){},
                            child: Row(
                              children: [
                                Container(
                                  margin: EdgeInsets.only(right: 20.0),
                                  padding: EdgeInsets.all(8.0),
                                  decoration: BoxDecoration(
                                    color: Colors.redAccent,
                                    borderRadius: BorderRadius.circular(12.0),
                                  ),
                                  child: Text(day),

                                ),
                                Expanded(child: Padding(  
                                  padding: EdgeInsets.all(9.0),

                                child:
                                
                                Text(task)),
                                ),
                              ],
                            ),
                          ),
                        );
                      },
                      ),
                      );
                    } else{
                      return Center(
                      child: Text('Enter Your Task'),
                      );
                    }
                  }
                
                case ConnectionState.none:
                  
                  break;
                case ConnectionState.active:
                 
                  break;
              }
            }
            )),
          Container(
             padding: EdgeInsets.symmetric(horizontal: 12.0,vertical: 18.0),
            decoration: BoxDecoration(color: editorColor,borderRadius: BorderRadius.only(
              topLeft: Radius.circular(19.0),
              topRight: Radius.circular(19.0),
            )),
            
            child: Row(
              children: [
                Expanded(child:TextField(
                  controller: inputcontroller,
                  decoration: InputDecoration(  
                    filled: true,
                    fillColor: Colors.white70,
                    hintText: "Enter Your Task",
                    focusedBorder: InputBorder.none,
                    
                  ),
                ),),
                SizedBox(width: 14.0),
                FlatButton.icon(icon: Icon(Icons.add), label: Text("Add  Task"),
                color: btnColor,
                shape: StadiumBorder(),
                onPressed: (){
                  setState(() {
                    newTasktxt=inputcontroller.text.toString();
                    inputcontroller.text='';
                  });
                  Task newTask=Task(task: newTasktxt,datetime: DateTime.now() );
                  DBProvider.dataBase. addnewtask(newTask);
                },),
                
              ],
            ),
          ),
        ],
      ),
    );
  }

  
}

*The body might complete normally, causing 'null' to be returned, but the return type is a potentially non-nullable type. Try adding either a return or a throw statement at the end. *The property 'length' can't be unconditionally accessed because the receiver can be 'null'. Try making the access conditional (using '?.') or adding a null check to the target ('!'). *The property 'length' can't be unconditionally accessed because the receiver can be 'null'. Try making the access conditional (using '?.') or adding a null check to the target ('!'). *The method '[]' can't be unconditionally invoked because the receiver can be 'null'. Try making the call conditional (using '?.') or adding a null check to the target ('!').

Answer 1

在您的 FutureBuilder 上，小部件不会针对所有可能的情况返回小部件，您需要处理其他状态，将 Container 替换为您的小部件。

 ....
 case ConnectionState.none:
  return Container();
case ConnectionState.active:
  return Container();
default:
  return Container();

第二个问题来自空安全，你需要检查数据是否为空，然后分配它

喜欢 itemCount

itemCount: taskData.data?.length,
 String task = taskData.data == null
    ? "no data found"
    : taskData.data![index]['task'].toString();

对其他人也这样做。

查看更多关于 null-safety

使用 Sqflite 时遇到 Flutter 中的错误

Facing Errors In Flutter When Using Sqflite

flutter

sqflite

dart-null-safety