我的Flutter App中有以下问题:
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 Plugin内的取消按钮时Navigate.pop()。
这个image_picker-Cancel问题的主要问题是:如何在Widget的构建器中导航回来(即Navigator.pop(context)
)?
以下引发错误:
Widget _cancelBtnPressedWidget(BuildContext context) {
Navigator.pop(context);
}
我知道Widget应该是return
的东西。因此可以伪返回一些东西 - 但实际上将Navigator.pop()保持为Widget中的主要动作??? (最好,在没有额外用户交互的情况下自动调用)......
从上面的代码,错误sais:
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)
.
这里更详细地描述了上述要求的来源:
事实上,我想在用户按下取消按钮时使用Navigator.pop()和image_picker
Plugin用法。
我意识到snapshot.hashCode
-change是检测取消按钮被用户按下的一种方法。因此,如果用户按下取消按钮,我只想将navigate.pop带回到我来自的地方;)...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。
这是进行图像查找的图像选择器部分 - 以及取消处理(即_cancelBtnPressedWidget
-Widget的调用)。
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中添加必要的依赖项:
dependencies:
flutter:
sdk: flutter
image_picker: ^0.5.0+3
添加在:
我试图添加一个确认对话框(即询问用户“你真的要取消”)。
现在,上述错误消失了。然而,现在image_picker
一次又一次地弹出......覆盖这个对话框。
我还在做什么呢?
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);
},
)
],
);
}
对我来说,似乎你根本没有抓住点击。对我来说,我会在_cancelBtnPressedWidget
中返回一个按钮,并在onPressed中调用pop。
我终于找到了答案:
实际上,我能够进行确认对话,在那里我能够放置必要的return Widget
。
现在,image_picker的取消按预期工作!
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();
}
}