我正在尝试创建一个简单的小部件,以便当用户按下屏幕时,该位置会出现一个圆圈。我有一个由Listener小部件包装的CustomPaint小部件,如下所示:
new Listener(
onPointerDown: down,
child: new CustomPaint(
painter: painter,
size: Size.infinite,
),
)
问题是指针向下事件是在全局坐标中提供的,并且绘制是在CustomPaint小部件的本地坐标中完成的。我该如何转换这两个坐标系?
This page说我可以使用RenderBox.globalToLocal方法但是如何获取CustomPaint小部件的RenderBox?
答案 0 :(得分:3)
您不一定要将侦听器包装在窗口小部件中。您还可以使用GlobalKey
获取RenderObject
。
import 'package:flutter/material.dart';
void main() {
runApp(new MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
home: new MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
@override
State createState() => new MyHomePageState();
}
class MyHomePageState extends State<MyHomePage> {
GlobalKey _paintKey = new GlobalKey();
Offset _offset;
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text('CustomPaint example'),
),
body: new Listener(
onPointerDown: (PointerDownEvent event) {
RenderBox referenceBox = _paintKey.currentContext.findRenderObject();
Offset offset = referenceBox.globalToLocal(event.position);
setState(() {
_offset = offset;
});
},
child: new CustomPaint(
key: _paintKey,
painter: new MyCustomPainter(_offset),
child: new ConstrainedBox(
constraints: new BoxConstraints.expand(),
),
),
),
);
}
}
class MyCustomPainter extends CustomPainter {
final Offset _offset;
MyCustomPainter(this._offset);
@override
void paint(Canvas canvas, Size size) {
if (_offset == null) return;
canvas.drawCircle(_offset, 10.0, new Paint()..color = Colors.blue);
}
@override
bool shouldRepaint(MyCustomPainter other) => other._offset != _offset;
}
答案 1 :(得分:0)
好的,这对我有用(感谢@mikemimik对gitter的帮助):
将侦听器包装在扩展StatelessWidget的新自定义窗口小部件中。然后该小部件的build()方法可以像这样访问RenderBox:
@override
Widget build(BuildContext context) {
void down(PointerDownEvent evt) {
RenderBox box = context.findRenderObject();
painter.addPos(box.globalToLocal(evt.position));
}
return new Listener(
onPointerDown: down,
child: new CustomPaint(
painter: painter,
size: Size.infinite,
),
);
}