如何在 Flutter 中实现可滚动的画布?
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【中文标题】如何在 Flutter 中实现可滚动的画布?【英文标题】:How to achieve scrollable canvas in Flutter? 【发布时间】:2019-01-24 01:55:37 【问题描述】:我是一位经验丰富的 ios 开发人员,但对 Flutter 完全陌生。现在我在 Flutter 中遇到了 ScrollView 的问题。
我想要实现的是构建一个大的可滚动画布。我之前在iOS上做过,你可以在这里看到截图。
canvas 是一个很大的 UIScrollView,canvas 上的每个 subview 都是可拖动的,所以我可以随意放置。即使文本很长,我也可以滚动画布以查看全部内容。现在我需要使用 Flutter 做同样的事情。
目前,我只能在 Flutter 中拖动文本小部件。但父小部件不可滚动。我知道我需要在 Flutter 中使用可滚动的小部件来获得相同的结果,但我就是无法让它工作。这是我目前拥有的代码。
void main()
//debugPaintLayerBordersEnabled = true;
//debugPaintSizeEnabled = true;
runApp(new MyApp());
class MyApp extends StatelessWidget
@override
Widget build(BuildContext context)
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.indigo,
),
home: new MyHomePage(title: 'Flutter Demo Drag Box'),
);
class MyHomePage extends StatelessWidget
MyHomePage(Key key, this.title) : super(key: key);
final String title;
@override
Widget build(BuildContext context)
return new Scaffold(
appBar: new AppBar(
title: new Text(title),
),
body: DragBox(Offset(0.0, 0.0)));
class DragBox extends StatefulWidget
final Offset position; // widget's position
DragBox(this.position);
@override
_DragBoxState createState() => new _DragBoxState();
class _DragBoxState extends State<DragBox>
Offset _previousOffset;
Offset _offset;
Offset _position;
@override
void initState()
_offset = Offset.zero;
_previousOffset = Offset.zero;
_position = widget.position;
super.initState();
@override
Widget build(BuildContext context)
return new Container(
constraints: BoxConstraints.expand(),
color: Colors.white24,
child: Stack(
children: <Widget>[
buildDraggableBox(1, Colors.red, _offset)
],
)
);
Widget buildDraggableBox(int boxNumber, Color color, Offset offset)
print('buildDraggableBox $boxNumber !');
return new Stack(
children: <Widget>[
new Positioned(
left: _position.dx,
top: _position.dy,
child: Draggable(
child: _buildBox(color, offset),
feedback: _buildBox(color, offset),
//childWhenDragging: _buildBox(color, offset, onlyBorder: true),
onDragStarted: ()
print('Drag started !');
setState(()
_previousOffset = _offset;
);
print('Start position: $_position');
,
onDragCompleted: ()
print('Drag complete !');
,
onDraggableCanceled: (Velocity velocity, Offset offset)
// update position here
setState(()
Offset _offset = Offset(offset.dx, offset.dy - 80);
_position = _offset;
print('Drag canceled position: $_position');
);
,
),
)
],
);
Widget _buildBox(Color color, Offset offset, bool onlyBorder: false)
return new Container(
child: new Text('Flutter widget',
textAlign: TextAlign.center,
style: new TextStyle(fontWeight: FontWeight.bold, fontSize: 25.0)),
);
任何建议或代码示例都会对我很有帮助。
PS:请忘记屏幕截图上的标尺,这对我来说不是最重要的。我现在只需要一个大的可滚动画布。
【问题讨论】:
“大”是什么意思? @creativecreatorormaybenot ah,我的错。只是意味着滚动视图将几乎占据整个屏幕。我会修正措辞。 你可以将你的视图包装成一个 SingleChildScollView 【参考方案1】:下面的代码可能有助于解决您在水平方向滚动自定义画布的问题,如您在示例图像中所示。
import 'package:flutter/material.dart';
class MyScroll extends StatelessWidget
@override
Widget build(BuildContext context)
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Canvas Scroller'),
);
class MyHomePage extends StatefulWidget
MyHomePage(Key key, this.title) : super(key: key);
final String title;
@override
_MyHomePageState createState() => new _MyHomePageState();
class _MyHomePageState extends State<MyHomePage>
@override
Widget build(BuildContext context)
final width = MediaQuery.of(context).size.width;
final height = MediaQuery.of(context).size.height;
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: new Center(
child: new SingleChildScrollView(
scrollDirection: Axis.horizontal,
child: new CustomPaint(
painter: new MyCanvasView(),
size: new Size(width*2, height/2),
),
),
),
);
class MyCanvasView extends CustomPainter
@override
void paint(Canvas canvas, Size size)
var paint = new Paint();
paint..shader = new LinearGradient(colors: [Colors.yellow[700], Colors.redAccent],
begin: Alignment.centerRight, end: Alignment.centerLeft).createShader(new Offset(0.0, 0.0)&size);
canvas.drawRect(new Offset(0.0, 0.0)&size, paint);
var path = new Path();
path.moveTo(0.0, size.height);
path.lineTo(1*size.width/4, 0*size.height/4);
path.lineTo(2*size.width/4, 2*size.height/4);
path.lineTo(3*size.width/4, 0*size.height/4);
path.lineTo(4*size.width/4, 4*size.height/4);
canvas.drawPath(path, new Paint()..color = Colors.yellow ..strokeWidth = 4.0 .. style = PaintingStyle.stroke);
@override
bool shouldRepaint(CustomPainter oldDelegate)
return false;
【讨论】:
谢谢。我已经实现了我的目标。 SingleChindScrollView 就是这样。顺便说一句,您的自定义绘画看起来很有趣。以上是关于如何在 Flutter 中实现可滚动的画布?的主要内容,如果未能解决你的问题,请参考以下文章
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