[英]Why Flutter CachedNetworkImage cannot put inside a Row or a Column?
問題主體有點長,但請閱讀並理解我的問題並幫助我。
非常感謝您提前
我有一個名為ImageWidget
的 class ,它擴展了StatefulWidget
,它返回一個GestureDetector
,它有一個子CachedNetworkImage
。 我的代碼正在運行,我可以調用此ImageWidget
class 並且如果我將其作為單個Widget
返回,則可以從任何地方顯示圖像。
像這樣(這些代碼都在工作)
return ImageWidget(
imageUrl: imageUrl,
);
return Container(
child: ImageWidget(
imageUrl: imageUrl,
));
return Center(
child: ImageWidget(
imageUrl: imageUrl,
));
我的目標是使用Row
或Column
或ListView
顯示此ImageWidget
的列表/多個。 我可以把這個ImageWidget
class 放到任何地方(例如Center
, Container
),除了需要多個孩子的Row
或Column
或ListView
。
像這樣(這些代碼不起作用;無法顯示圖像;也沒有錯誤)
return Column(
children: <Widget>[
ImageWidget(
imageUrl: imageUrl,
),
ImageWidget(
imageUrl: imageUrl,
),
ImageWidget(
imageUrl: imageUrl,
)
],
);
每當我將ImageWidget
放到這些Widgets
中的任何一個( Row
或Column
或ListView
)時,圖像都不會顯示。 我認為問題出在imageBuilder
上,因為當我將其刪除或將其設置為null
時,它可以工作,但我做不到,我需要保持圖像的形狀。
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),
)
);
}
}
如果我將ImageWidget
放到CircularAvatar
上而不是正常工作,我可以將它放在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,我不能這樣做,因為圖像已損壞並且我不想要圓形圖像。 我需要保持一個矩形BoxFit.contain
形狀。
您的 ImageWidget 可以使用 Row 和 Column
用 Container 包裹 CachedNetworkImage 並設置高度/寬度
對於占位符,可以使用 Container(),這樣 CircularProgressIndicator 就不會顯示
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),
),
)
像這樣打電話
ImageWidget(
imageUrl: 'http://via.placeholder.com/350x150',
shape: BoxShape.rectangle,
fit: BoxFit.fill,
),
完整代碼
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),
),
));
}
}
您需要做的是給出可以從MediaQuery.of(context).size.width
獲得的設備寬度
然后設置CachedNetworkImage的這兩個屬性
CachedNetworkImage(
width: width,
fit: BoxFit.fitWidth,
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