Why Flutter CachedNetworkImage cannot put inside a Row or a Column?

Question

The question body is a little long but please read and understand my problem and help me out.

Thank you very much in advance

I have a class called ImageWidget which extends StatefulWidget , it returns a GestureDetector which has a child CachedNetworkImage . My code is working, I'm able to call this ImageWidget class and able to display the image from anywhere if I return it as a single Widget .

Like this (These codes are all working)

return ImageWidget(
      imageUrl: imageUrl,
    );

return Container(
        child: ImageWidget(
      imageUrl: imageUrl,
    ));

return Center(
        child: ImageWidget(
      imageUrl: imageUrl,
    ));

My goal here is to display a list/multiple of this ImageWidget by using a Row or Column or ListView . I can put this ImageWidget class to anywhere (such as Center , Container ) except Row or Column or ListView which takes multiple children.

Like this (These code doesn't work; not able to display the image; also no error)

return Column(
      children: <Widget>[
        ImageWidget(
          imageUrl: imageUrl,
        ),
        ImageWidget(
          imageUrl: imageUrl,
        ),
        ImageWidget(
          imageUrl: imageUrl,
        )
      ],
    );

Whenever I put my ImageWidget to any of these Widgets ( Row or Column or ListView ) the image doesn't show up. I think the problem is with the imageBuilder because when I remove it or set it to null it works but I can't do it, I need to maintain the shape of the image.

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),
            )
        );
      }
    }

If I put the ImageWidget to a CircularAvatar than it works, I can put it in a Row or Column .

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,
          ),
        ),
      ],
    );

also, I can't do it because the image is broken and I don't want the circular image. I need to maintain a rectangular BoxFit.contain shape.

Answer 1

Your ImageWidget can work with Row and Column
Wrap CachedNetworkImage with Container and set height/width
For placeholder, you can use Container(), so CircularProgressIndicator will not show

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),
          ),
        )

and call like this

ImageWidget(
              imageUrl: 'http://via.placeholder.com/350x150',
              shape: BoxShape.rectangle,
              fit: BoxFit.fill,
            ),

full code

    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),
            ),
        ));
  }
}

Answer 2

What you need to do is give the width of the device which you can get from MediaQuery.of(context).size.width

Then set these two properties of CachedNetworkImage

  CachedNetworkImage(
              width: width,
              fit: BoxFit.fitWidth,