我被困在這個空錯誤上，我無法修復這個錯誤，上面寫著“錯誤：引數型別'Null'不能分配給引數型別'int'。” 錯誤顯示在選定的：null，行。我在下面添加了我的代碼，希望有人能提供幫助。讓我知道是否需要任何其他代碼。
floatingActionButton: FloatingActionButton(
child: Icon(Icons.add),
onPressed: () async {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => StudyPage(
title: 'Add a study',
selected: null,
)));
添加
import 'package:flutter/material.dart';
import 'package:timestudy_test/models/study.dart';
import 'package:timestudy_test/models/task.dart';
import 'package:timestudy_test/viewmodels/study_viewmodel.dart';
class StudyPage extends StatefulWidget {
final String title;
final int selected;
StudyPage({required this.title, required this.selected});
@override
State createState() => StudyPageState();
}
class StudyPageState extends State<StudyPage> {
late Study study;
late TextField nameField;
TextEditingController nameController = new TextEditingController();
late TextField taskNameField;
TextEditingController taskNameController = new TextEditingController();
@override
void initState() {
nameField = new TextField(
controller: nameController,
decoration: InputDecoration(
labelText: 'Study name'),
);
taskNameField = new TextField(
controller: taskNameController,
decoration:
InputDecoration(labelText: 'Task name'),
);
if(widget.selected != null) {
study = StudyViewModel.studies[widget.selected];
nameController.text = study.name;
} else {
study = new Study(
name: "",
tasks: <Task>[]
);
}
super.initState();
}
@override
void dispose() {
nameController.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
return Scaffold(
resizeToAvoidBottomInset: false,
appBar: AppBar(
title: Text(widget.title),
),
body: Material(
child: Padding(padding: EdgeInsets.all(16.0), child: Column(
children: <Widget>[
Padding(padding: EdgeInsets.only(bottom: 8.0), child: nameField),
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text('Tasks:', style: TextStyle(fontSize: 18.0),),
IconButton(
icon: Icon(Icons.add),
onPressed: () async {
await showDialog(
context: context,
builder: (context) {
return AlertDialog(
title: Text('Add a task'),
content: taskNameField,
actions: <Widget>[
FlatButton(
child: Text('Cancel'),
onPressed: () {
Navigator.of(context).pop();
},
),
FlatButton(
child: Text('Accept'),
onPressed: () {
if(taskNameController.text == ""){
errorDialog(context, 'Please enter a task name!');
} else {
setState(() {
study.tasks.add(new Task(
name: taskNameController.text,
elapsedTime:
StudyViewModel.milliToElapsedString(
0)));
taskNameController.clear();
});
Navigator.of(context).pop();
}
},
),
],
);
});
},
)
],
),
Expanded(
child: ListView.builder(
itemCount: study.tasks.length,
itemBuilder: (context, int index) {
return ListTile(
title: Text(study.tasks[index].name),
trailing: IconButton(
icon: Icon(Icons.delete),
onPressed: () {
setState(() {
study.tasks.removeAt(index);
});
},
),
);
},
),
), Spacer(),
Center(
child: RaisedButton(
color: Theme.of(context).accentColor,
child: Text('Save'),
onPressed: () async {
if (nameController.text == "") {
errorDialog(context, 'Please enter a study name!');
} else {
if (study.tasks.length < 1) {
errorDialog(context, 'Please add at least one task!');
} else {
study.name = nameController.text;
if (widget.selected != null) {
StudyViewModel.studies[widget.selected] = study;
await StudyViewModel.saveFile();
Navigator.of(context).pop();
} else {
if (StudyViewModel.checkName(nameController.text)) {
errorDialog(context, 'Study name already taken!');
} else {
StudyViewModel.studies.add(study);
await StudyViewModel.saveFile();
Navigator.of(context).pop();
}
}
}
}
},
))
],
),
)));
}
void errorDialog(BuildContext context, String message) async {
await showDialog(
context: context,
builder: (context) {
return AlertDialog(
content: Text(message),
actions: <Widget>[
FlatButton(
child: Text('Close'),
onPressed: () {
Navigator.of(context).pop();
},
)
],
);
}
);
}
}
uj5u.com熱心網友回復：
您不能將值 null 分配給非 Null 變數
整數選擇；<------- 它只允許0,1,2,3等int值，并繼續
如果您嘗試將值傳遞給此頁面，您可以檢查該值是整數還是空值
int? nullableInterger;
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => StudyPage(
title: 'Add a study',
selected: nullableInterger ?? 0,// here 0 is const value you can chose whatever you want
)));
uj5u.com熱心網友回復：
您不能傳遞null給非空屬性
class StudyPage extends StatefulWidget {
final String title;
final int selected;
.....
change to
class StudyPage extends StatefulWidget {
final String title;
final int? selected; <<<-----
uj5u.com熱心網友回復：
您必須將 StudyPage 的選定引數指定為可為空。這樣做
編輯此代碼：
class StudyPage extends StatefulWidget {
final String title;
final int selected;
StudyPage({required this.title, required this.selected});
@override
State createState() => StudyPageState();
}
并將其更改為
class StudyPage extends StatefulWidget {
final String title;
final int? selected;
StudyPage({required this.title, required this.selected});
@override
State createState() => StudyPageState();
}
uj5u.com熱心網友回復：
在你的 study_page.dart 添加 '?' 使選定的可選資料型別同時接受 int 和 null 值。
class StudyPage extends StatefulWidget {
final String title;
final int? selected;
StudyPage({required this.title, required this.selected});
@override
State createState() => StudyPageState();
}
在 StudyViewModel 中，將研究引數設為可選int? studies;
轉載請註明出處，本文鏈接：https://www.uj5u.com/qiye/431290.html
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