【发布时间】：2021-07-01 11:06:16
【问题描述】：
我已经实现了一个允许用户在我的颤振应用程序中输入的 TextField。现在，我想在按下按钮时将用户输入数据保存到变量中，以便以后使用。正如我所看到的，为了实现这一点，我必须创建有状态小部件及其状态的特定实例，以便当我调用小部件以提取变量时，它不会创建带有空文本字段。有问题的文本字段是 ProjectNameField 和 ProjectDescriptionField。 这是我的实现：
ProjectDescriptionField savedDescription = ProjectDescriptionField();
ProjectNameField savedName = ProjectNameField();
AddPage savedPage = AddPage();
_AddPageState savedPageState = _AddPageState();
List<String> image_list_encoded = [];
class AddPage extends StatefulWidget {
final _AddPageState _addPageState = _AddPageState();
AddPage({Key? key}) : super(key: key);
@override
_AddPageState createState() => _AddPageState();
}
class _AddPageState extends State<AddPage> {
List<Asset> images = <Asset>[];
String _error = NOERROR;
@override
Widget build(BuildContext context) {
if (images.isEmpty)
return AppLayout(logicalHeight * 0.15);
else
return AppLayout(logicalHeight * 0.01);
}
List<Asset> getImages() {
return images;
}
Widget AppLayout(double distanceFromImages) {
return Scaffold(
appBar: AppBar(
leading: BackButton(color: Colors.white),
title: Text(CREATEPROJECT),
actions: <Widget>[
IconButton(
icon: Icon(
Icons.check,
color: Colors.white,
),
onPressed: () {
SavedData _savedData = SavedData(
savedName._nameFieldState.myController.value.text,
savedDescription
._descriptionFieldState.myController.value.text,
savedPage._addPageState.getImages());
print(_savedData.saved_Project_Description);
print(_savedData.saved_Project_Name);
print(_savedData.saved_images.toString());
saveNewProject(_savedData);
},
),
],
),
body: Column(children: <Widget>[
Padding(
padding: EdgeInsets.fromLTRB(0, logicalHeight * 0.02, 0, 0),
child: Center(
child: Container(
height: logicalHeight * 0.05,
width: logicalWidth * 0.9,
child: savedName)),
),
Padding(
padding: EdgeInsets.fromLTRB(0, logicalHeight * 0.01, 0, 0),
child: ElevatedButton(
child: Text(PICKIMAGES),
onPressed: loadAssets,
)),
Center(
child: Padding(
padding: EdgeInsets.fromLTRB(0, logicalHeight * 0.01, 0, 0),
child: getWidget())),
Padding(
padding: EdgeInsets.fromLTRB(
logicalWidth * 0.05, distanceFromImages, logicalWidth * 0.05, 0),
child: Center(child: Container(child: savedDescription)),
),
]),
);
}
Widget getWidget() {
if (images.length > 0) {
return Container(
height: logicalHeight * 0.4,
width: logicalWidth * 0.8,
child: ImagePages());
} else {
return Padding(
padding: EdgeInsets.fromLTRB(0, logicalHeight * 0.15, 0, 0),
child: Container(child: Text(NOPICTURESSELECTED)));
}
}
PageView ImagePages() {
final PageController controller = PageController(initialPage: 0);
List<Widget> children = [];
images.forEach((element) {
children.add(Padding(
padding: EdgeInsets.fromLTRB(
logicalWidth * 0.01, 0, logicalWidth * 0.01, 0),
child: AssetThumb(
asset: element,
width: 1000,
height: 1000,
)));
});
return PageView(
scrollDirection: Axis.horizontal,
controller: controller,
children: children,
);
}
}
class ProjectNameField extends StatefulWidget {
ProjectNameFieldState _nameFieldState = ProjectNameFieldState();
@override
ProjectNameFieldState createState() {
return _nameFieldState;
}
}
class ProjectNameFieldState extends State<ProjectNameField> {
final myController = TextEditingController();
@override
void dispose() {
// Clean up the controller when the widget is disposed.
myController.dispose();
super.dispose();
}
Widget build(BuildContext context) {
return TextField(
controller: myController,
decoration: InputDecoration(
border: UnderlineInputBorder(),
hintText: PROJECTNAME,
),
maxLength: 30,
);
}
}
class ProjectDescriptionField extends StatefulWidget {
ProjectDescriptionFieldState _descriptionFieldState =
ProjectDescriptionFieldState();
@override
ProjectDescriptionFieldState createState() {
return _descriptionFieldState;
}
}
class ProjectDescriptionFieldState extends State<ProjectDescriptionField> {
final myController = TextEditingController();
@override
void dispose() {
// Clean up the controller when the widget is disposed.
myController.dispose();
super.dispose();
}
Widget build(BuildContext context) {
return TextField(
controller: myController,
decoration: InputDecoration(
border: UnderlineInputBorder(),
hintText: PROJECTDESCRIPTION,
),
minLines: 1,
maxLines: 5,
maxLength: 5000,
);
}
}
class SavedData {
String saved_Project_Name = "";
String saved_Project_Description = "";
List<Asset> saved_images = [];
SavedData(String saved_Project_Name, String saved_Project_Description,
List<Asset> saved_images) {
this.saved_Project_Name = saved_Project_Name;
this.saved_Project_Description = saved_Project_Description;
this.saved_images = saved_images;
}
}
我认为问题出在此处（ProjectNameField 和 ProjectDescriptionField 基本相同，只有细微差别）：
class ProjectNameField extends StatefulWidget {
ProjectNameFieldState _nameFieldState = ProjectNameFieldState();
@override
ProjectNameFieldState createState() {
return _nameFieldState;
}
}
class ProjectNameFieldState extends State<ProjectNameField> {
final myController = TextEditingController();
@override
void dispose() {
// Clean up the controller when the widget is disposed.
myController.dispose();
super.dispose();
}
Widget build(BuildContext context) {
return TextField(
controller: myController,
decoration: InputDecoration(
border: UnderlineInputBorder(),
hintText: PROJECTNAME,
),
maxLength: 30,
);
}
}
当我让 createState() 返回 _nameFieldState 而不是 ProjectNameFieldState() 时，会出现以下错误：
The createState function for ProjectDescriptionField returned an old or invalid state instance: ProjectDescriptionField, which is not null, violating the contract for createState.
'package:flutter/src/widgets/framework.dart':
Failed assertion: line 4681 pos 7: 'state._widget == null'
但是，当我返回 ProjectNameFieldState() 时，则此代码
onPressed: () {
SavedData _savedData = SavedData(
savedName._nameFieldState.myController.value.text,
savedDescription
._descriptionFieldState.myController.value.text,
savedPage._addPageState.getImages());
print(_savedData.saved_Project_Description);
print(_savedData.saved_Project_Name);
print(_savedData.saved_images.toString());
saveNewProject(_savedData);
}
不保存项目名称。 我怎样才能摆脱这个错误并保存项目名称和项目描述？ 谢谢！
【问题讨论】：
标签： ios flutter statefulwidget