编辑您的新代码运行良好，但您看不到这个圆圈，因为 paint.strokeWidth 为 1 请更改为 10
在新的完整代码中，我也PhotoView使用Container并设置height
代码片段paint.strokeWidth = 10
final paint = new Paint();
paint.strokeWidth = 10;
paint.color = const Color(0xFF0000FF);
paint.style = PaintingStyle.stroke;
新的完整代码
import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';
import 'package:photo_view/photo_view.dart';
import 'package:flutter/services.dart' show rootBundle;
import 'dart:convert';
import 'dart:ui' as ui;
import 'dart:typed_data';
import 'dart:async';
import 'dart:io';
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: TestImageDraw(
title: "test",
),
);
}
}
class TestImageDraw extends StatefulWidget {
TestImageDraw({Key key, this.title}) : super(key: key);
final String title;
@override
_TestImageDrawState createState() => _TestImageDrawState();
}
class _TestImageDrawState extends State<TestImageDraw> {
ImageProvider _imageProvider;
@override
void initState() {
super.initState();
_imageProvider = NetworkImage(
"https://www.google.com/images/branding/googlelogo/2x/googlelogo_color_92x30dp.png");
}
_generateImage() {
GenImage.generateImage().then((generatedImage) async {
ByteData image =
await generatedImage.toByteData(format: ui.ImageByteFormat.png);
// String base64 = base64Encode(image.buffer.asInt64List());
// print(base64);
// Uint8List bytes = base64Decode(base64);
// _imageProvider = MemoryImage(bytes);
_imageProvider = MemoryImage(image.buffer.asUint8List());
setState(() {});
});
}
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: SingleChildScrollView(
child: Container(
child: Column(children: <Widget>[
//Image will display
//Image(image: _imageProvider),
Container(
height: 300,
child: _imageProvider != null
? PhotoView(imageProvider: _imageProvider)
: Container()),
])),
),
floatingActionButton: new FloatingActionButton(
onPressed: _generateImage,
tooltip: 'Generate',
child: new Icon(Icons.add),
),
);
}
}
class GenImage {
static Future<ui.Image> generateImage() async {
ui.PictureRecorder recorder = new ui.PictureRecorder();
Canvas c = new Canvas(recorder);
var rect = new Rect.fromLTWH(0.0, 0.0, 200.0, 200.0);
c.clipRect(rect);
final paint = new Paint();
paint.strokeWidth = 10;
paint.color = const Color(0xFF0000FF);
paint.style = PaintingStyle.stroke;
final offset = new Offset(100.0, 100.0);
c.drawCircle(offset, 50.0, paint);
var picture = recorder.endRecording();
final image = await picture.toImage(500, 500);
return image;
}
}
照片视图可以正常工作MemoryImage，您可以在下面复制粘贴运行完整代码
您遇到的错误可能是显示时图像未准备好
您可以检查pngBytes == null return Container()
代码片段
children: <Widget>[
bytes == null
? Container()
: Expanded(
flex: 1,
child: PhotoView(
imageProvider: MemoryImage(bytes),
),
),
工作演示动画 gif
完整代码
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:photo_view/photo_view.dart';
import 'package:http/http.dart' as http;
import 'dart:typed_data';
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;
String _base64;
Uint8List bytes;
void _incrementCounter() {
(() async {
http.Response response = await http.get(
'https://picsum.photos/250?image=9',
);
if (mounted) {
setState(() {
_base64 = base64Encode(response.bodyBytes);
print(_base64);
bytes = base64Decode(_base64);
});
}
})();
}
@override
void initState() {
super.initState();
/* (() async {
http.Response response = await http.get(
'https://picsum.photos/250?image=9',
);
if (mounted) {
setState(() {
_base64 = base64Encode(response.bodyBytes);
print(_base64);
bytes = base64Decode(_base64);
});
}
})();*/
}
@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>[
bytes == null
? Container()
: Expanded(
flex: 1,
child: PhotoView(
imageProvider: MemoryImage(bytes),
),
),
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}