假设我在pubspec.yaml中声明了我的图像，如下所示:
assets:
- assets/kitten.jpg
我的Flutter 代码是这样的:
void main() {
runApp(
new Center(
child: new Image.asset('assets/kitten.jpg'),
),
);
}
现在我有了new Image.asset()，我该如何确定该图像的宽度和高度呢？例如，我只想打印出图像的宽度和高度.
(看起来dart:ui's Image class有宽和高，但不确定如何从小部件的Image转到DART:UI的Image.)
谢谢
随着Flutter 的新版本，旧的解决方案已经过时了.现在addListener分需要ImageStreamListener分.
Widget build(BuildContext context) {
Image image = new Image.network('https://i.stack.imgur.com/lkd0a.png');
Completer<ui.Image> completer = new Completer<ui.Image>();
image.image
.resolve(new ImageConfiguration())
.addListener(ImageStreamListener((ImageInfo info, bool _) {
completer.complete(info.image));
})
...
...
如果你已经有了一个Image小部件，你可以通过拨打resolve的ImageProvider来读取其中的ImageStream.
import 'dart:ui' as ui;
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
void main() {
runApp(new MaterialApp(
home: new MyHomePage(),
));
}
class MyHomePage extends StatelessWidget {
Widget build(BuildContext context) {
Image image = new Image.network('https://i.stack.imgur.com/lkd0a.png');
Completer<ui.Image> completer = new Completer<ui.Image>();
image.image
.resolve(new ImageConfiguration())
.addListener((ImageInfo info, bool _) => completer.complete(info.image));
return new Scaffold(
appBar: new AppBar(
title: new Text("Image Dimensions Example"),
),
body: new ListView(
children: [
new FutureBuilder<ui.Image>(
future: completer.future,
builder: (BuildContext context, AsyncSnapshot<ui.Image> snapshot) {
if (snapshot.hasData) {
return new Text(
'${snapshot.data.width}x${snapshot.data.height}',
style: Theme.of(context).textTheme.display3,
);
} else {
return new Text('Loading...');
}
},
),
image,
],
),
);
}
}