[英]Why Flutter CachedNetworkImage cannot put inside a Row or a Column?
问题主体有点长,但请阅读并理解我的问题并帮助我。
非常感谢您提前
我有一个名为ImageWidget
的 class ,它扩展了StatefulWidget
,它返回一个GestureDetector
,它有一个子CachedNetworkImage
。 我的代码正在运行,我可以调用此ImageWidget
class 并且如果我将其作为单个Widget
返回,则可以从任何地方显示图像。
像这样(这些代码都在工作)
return ImageWidget(
imageUrl: imageUrl,
);
return Container(
child: ImageWidget(
imageUrl: imageUrl,
));
return Center(
child: ImageWidget(
imageUrl: imageUrl,
));
我的目标是使用Row
或Column
或ListView
显示此ImageWidget
的列表/多个。 我可以把这个ImageWidget
class 放到任何地方(例如Center
, Container
),除了需要多个孩子的Row
或Column
或ListView
。
像这样(这些代码不起作用;无法显示图像;也没有错误)
return Column(
children: <Widget>[
ImageWidget(
imageUrl: imageUrl,
),
ImageWidget(
imageUrl: imageUrl,
),
ImageWidget(
imageUrl: imageUrl,
)
],
);
每当我将ImageWidget
放到这些Widgets
中的任何一个( Row
或Column
或ListView
)时,图像都不会显示。 我认为问题出在imageBuilder
上,因为当我将其删除或将其设置为null
时,它可以工作,但我做不到,我需要保持图像的形状。
ImageWidget.dart class
import 'package:analog_components/Utilities/MessageUnilities.dart';
import 'package:cached_network_image/cached_network_image.dart';
import 'package:flutter/material.dart';
class ImageWidget extends StatefulWidget {
final String imageUrl;
final BoxShape shape;
final BoxFit fit;
ImageWidget(
{this.imageUrl, this.shape: BoxShape.rectangle, this.fit: BoxFit.contain})
: assert(imageUrl != null),
assert(shape != null),
assert(fit != null);
@override
State<StatefulWidget> createState() {
return _ImageWidget();
}
}
class _ImageWidget extends State<ImageWidget> {
@override
Widget build(BuildContext context) {
print('image widget');
return GestureDetector(
onTap: () {
MessageUtilities.showShortToast('tap');
},
child: CachedNetworkImage(
imageUrl: widget.imageUrl,
placeholder: (context, url) => CircularProgressIndicator(),
imageBuilder: (context, imageProvider) => Container(
decoration: BoxDecoration(
shape: widget.shape,
image: DecorationImage(
image: imageProvider,
fit: widget.fit,
),
),
),
errorWidget: (context, url, error) => Icon(Icons.error),
)
);
}
}
如果我将ImageWidget
放到CircularAvatar
上而不是正常工作,我可以将它放在Row
或Column
中。
return Column(
children: <Widget>[
CircleAvatar(
radius: 50,
child: ImageWidget(
imageUrl: imageUrl,
),
),
CircleAvatar(
radius: 50,
child: ImageWidget(
imageUrl: imageUrl,
),
),
CircleAvatar(
radius: 50,
child: ImageWidget(
imageUrl: imageUrl,
),
),
],
);
另外,我不能这样做,因为图像已损坏并且我不想要圆形图像。 我需要保持一个矩形BoxFit.contain
形状。
您的 ImageWidget 可以使用 Row 和 Column
用 Container 包裹 CachedNetworkImage 并设置高度/宽度
对于占位符,可以使用 Container(),这样 CircularProgressIndicator 就不会显示
child: Container(
height: 200,
child: CachedNetworkImage(
imageUrl: widget.imageUrl,
placeholder: (context, url) => Container(),
imageBuilder: (context, imageProvider) => Container(
decoration: BoxDecoration(
shape: widget.shape,
image: DecorationImage(
image: imageProvider,
fit: widget.fit,
),
),
),
errorWidget: (context, url, error) => Icon(Icons.error),
),
)
像这样打电话
ImageWidget(
imageUrl: 'http://via.placeholder.com/350x150',
shape: BoxShape.rectangle,
fit: BoxFit.fill,
),
完整代码
import 'package:flutter/material.dart';
import 'package:cached_network_image/cached_network_image.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
// This is the theme of your application.
//
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to Colors.green and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or simply save your changes to "hot reload" in a Flutter IDE).
// Notice that the counter didn't reset back to zero; the application
// is not restarted.
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
_counter++;
});
}
@override
Widget build(BuildContext context) {
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return Scaffold(
appBar: AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: Text(widget.title),
),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
// Column is also a layout widget. It takes a list of children and
// arranges them vertically. By default, it sizes itself to fit its
// children horizontally, and tries to be as tall as its parent.
//
// Invoke "debug painting" (press "p" in the console, choose the
// "Toggle Debug Paint" action from the Flutter Inspector in Android
// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
// to see the wireframe for each widget.
//
// Column has various properties to control how it sizes itself and
// how it positions its children. Here we use mainAxisAlignment to
// center the children vertically; the main axis here is the vertical
// axis because Columns are vertical (the cross axis would be
// horizontal).
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Expanded(
flex: 1,
child: ImageWidget(
imageUrl: 'http://via.placeholder.com/350x150',
shape: BoxShape.rectangle,
fit: BoxFit.fill,
),
),
Expanded(
flex: 1,
child: ImageWidget(
imageUrl: 'http://via.placeholder.com/350x150',
shape: BoxShape.rectangle,
fit: BoxFit.fill,
),
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
class ImageWidget extends StatefulWidget {
final String imageUrl;
final BoxShape shape;
final BoxFit fit;
ImageWidget(
{this.imageUrl, this.shape: BoxShape.rectangle, this.fit: BoxFit.contain})
: assert(imageUrl != null),
assert(shape != null),
assert(fit != null);
@override
State<StatefulWidget> createState() {
return _ImageWidget();
}
}
class _ImageWidget extends State<ImageWidget> {
@override
Widget build(BuildContext context) {
print('image widget');
return GestureDetector(
onTap: () {
//MessageUtilities.showShortToast('tap');
print("tap");
},
child: Container(
child: CachedNetworkImage(
imageUrl: widget.imageUrl,
placeholder: (context, url) => Container(height: 0, width: 0,),
imageBuilder: (context, imageProvider) => Container(
decoration: BoxDecoration(
shape: widget.shape,
image: DecorationImage(
image: imageProvider,
fit: widget.fit,
),
),
),
errorWidget: (context, url, error) => Icon(Icons.error),
),
));
}
}
您需要做的是给出可以从MediaQuery.of(context).size.width
获得的设备宽度
然后设置CachedNetworkImage的这两个属性
CachedNetworkImage(
width: width,
fit: BoxFit.fitWidth,
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