image_picker取消:Flutter的Widget生成器中的Navigation.pop

Question

我的Flutter应用程序中存在以下问题：

为了使image_picker取消按钮正常工作，我需要能够在用户按下image_picker插件内的取消按钮时导航.pop()。

这个image_picker-Cancel问题的主要问题是：如何在Widget的构建器中导航回(即Navigator.pop(context))？

以下抛出错误：

Widget _cancelBtnPressedWidget(BuildContext context) {
Navigator.pop(context);
}

我知道Widget应该是return之类的东西。因此，是否可以伪返回一些东西，但实际上保持Navigator.pop()作为Widget内的主要操作？？？(最好是在没有额外用户交互的情况下自动调用)。。。

从上面的代码来看，错误是：

flutter: ══╡ EXCEPTION CAUGHT BY ANIMATION LIBRARY ╞═════════════════════════════════════════════════════════
flutter: The following assertion was thrown while notifying status listeners for AnimationController:
flutter: setState() or markNeedsBuild() called during build.
flutter: This Overlay widget cannot be marked as needing to build because the framework is already in the
flutter: process of building widgets. A widget can be marked as needing to be built during the build phase
flutter: only if one of its ancestors is currently building. This exception is allowed because the framework
flutter: builds parent widgets before children, which means a dirty descendant will always be built.
flutter: Otherwise, the framework might not visit this widget during this build phase.
flutter: The widget on which setState() or markNeedsBuild() was called was:
flutter:   Overlay-[LabeledGlobalKey<OverlayState>#b5c98](state: OverlayState#6a872(entries:
flutter:   [OverlayEntry#cd1e7(opaque: false; maintainState: false), OverlayEntry#43b81(opaque: false;
flutter:   maintainState: true), OverlayEntry#f0b49(opaque: false; maintainState: false),
flutter:   OverlayEntry#b9362(opaque: false; maintainState: true)]))
flutter: The widget which was currently being built when the offending call was made was:
flutter:   FutureBuilder<File>(dirty, state: _FutureBuilderState<File>#d3cac)

以下是对上述要求来源的更详细描述：

事实上，对于image_picker插件的使用，我希望在用户按下取消按钮后立即使用Navigator.pop()。

我意识到snapshot.hashCode-更改是检测用户按下取消按钮的一种方法。因此，如果用户按下Cancel按钮，我只想导航.pop回到我的家乡；)。。。我不想再显示或将用户保留在Widget中，但立即返回到最初Navigate.pushed.的视图

这里是执行图像查找和取消处理(即调用_cancelBtnPressedWidget-Widget)的图像选择器部分。

import 'package:flutter/material.dart';
import 'dart:io';
import 'package:image_picker/image_picker.dart';
File _imageFile;
bool _pickImage = true;
int _hashy = 0;
@override
Widget build(BuildContext context) {
if (_pickImage) {
return FutureBuilder<File>(
future: ImagePicker.pickImage(source: ImageSource.camera),
builder: (BuildContext context, AsyncSnapshot<File> snapshot) {
if (snapshot.hasData) {
_pickImage = false;
_imageFile = snapshot.data;
return _showImage(snapshot.data);
} else {
// when cancel is pressed, the hashCode changes...
if ((_hashy != 0) && (snapshot.hashCode != _hashy)) {
// when cancel pressed
return _cancelBtnPressedWidget(context);
}
_hashy = snapshot.hashCode;
return Scaffold(
body: Center(
child: Text('no image picker available'),
),
);
}
},
);
} else {
return _showImage(_imageFile);
}
}

Widget _cancelBtnPressedWidget(BuildContext context) {
// requires a return ..... How to overcome this requirement ????
Navigator.pop(context);
}

Widget _showImage(File imgFile) {
return Scaffold(
body: SafeArea(
child: Stack(
alignment: AlignmentDirectional.topStart,
children: <Widget>[
Positioned(
left: 0.0,
bottom: 0.0,
width: MediaQuery.of(context).size.width,
height: MediaQuery.of(context).size.height,
child: Center(
child: imgFile == null
? Text('No image selected.')
: Image.file(imgFile),
),
),
// more stacks ... not important here....
],
),
),
);
}

当然，在pubspec.yaml中，您添加了必要的依赖项：

dependencies:
flutter:
sdk: flutter
image_picker: ^0.5.0+3

附加组件：

我尝试添加一个确认对话框(即询问用户"你真的想取消吗")。

现在，上述错误已经消失。然而，现在image_picker一次又一次地弹出。。。覆盖此对话框。

我还在做什么对不起她？？

Widget _cancelBtnPressedWidget(BuildContext context) {
return AlertDialog(
title: Text('Camera Alert'),
content: Text('Are you sure you want to cancel ?'),
actions: <Widget>[
FlatButton(
child: Text('Close'),
onPressed: () {
Navigator.pop(context);
},
)
],
);
}

Answer 1

我终于找到了答案：

事实上，我可以放置一个确认对话框，并在那里放置必要的return Widget。

现在image_picker的Cancel正在按预期工作！

这是整个代码：

import 'package:flutter/material.dart';
import 'dart:io';
import 'package:image_picker/image_picker.dart';
class MyImagePickerView extends StatefulWidget {
_MyImagePickerViewState createState() => _MyImagePickerViewState();
}
class _MyImagePickerViewState extends State<MyImagePickerView> {
File _imageFile;
bool _pickImage = true;
int _hashy = 0;
bool _cancelPressed = false;
@override
Widget build(BuildContext context) {
if (_pickImage) {
return FutureBuilder<File>(
future: ImagePicker.pickImage(source: ImageSource.camera),
builder: (BuildContext context, AsyncSnapshot<File> snapshot) {
if (snapshot.hasData) {
_pickImage = false;
_imageFile = snapshot.data;
return _showImage(snapshot.data);
} else {
// when cancel is pressed, the hashCode changes...
if ((_hashy != 0) && (snapshot.hashCode != _hashy)) {
// when cancel pressed
return _cancelBtnPressedWidget(context);
}
_hashy = snapshot.hashCode;
return Scaffold(
body: Center(
child: Text('no image picker available'),
),
);
}
},
);
} else {
if (_cancelPressed) {
return _showAlert();
} else {
return _showImage(_imageFile);
}
}
}
Widget _cancelBtnPressedWidget(BuildContext context) {
_cancelPressed = true;
_pickImage = false;
return Scaffold(
body: Center(
child: Text('Press button to start.'),
),
);
}
Widget _showImage(File imgFile) {
StateContainerState container = StateContainer.of(context);
return Scaffold(
body: SafeArea(
child: Stack(
alignment: AlignmentDirectional.topStart,
children: <Widget>[
Positioned(
left: 0.0,
bottom: 0.0,
width: MediaQuery.of(context).size.width,
height: MediaQuery.of(context).size.height,
child: Center(
child: imgFile == null
? Text('No image selected.')
: Image.file(imgFile),
),
),
// more stacks ... not important here....
],
),
),
);
}
Widget _showAlert() {
return AlertDialog(
title: Text('Camera Alert'),
content: Text('Are you sure you want to cancel the Camera ?'),
actions: <Widget>[
FlatButton(
child: Text('No'),
onPressed: () {
setState(() {
_pickImage = true;
_cancelPressed = false;
});
},
),
FlatButton(
child: Text('Yes'),
onPressed: () {
Navigator.pop(context);
},
),
],
);
}
@override
void dispose() {
_myController.dispose();
super.dispose();
}
}

Answer 2

对我来说，你似乎根本没有捕捉到点击。对我来说，我会在_cancelBtnPressedWidget中返回一个按钮，并在onPressed中调用pop。