你需要追踪矩形位置的状态,与画布绘制独立。最简单的方法是使用StatefulWidget来实现。你还需要使用GestureDetector来捕获pan事件。然后将手势细节连接到矩形的位置,并调用绘图器重新绘制所有内容。
这是一个演示如何在一个矩形中完成上述操作的简单应用程序。扩展到处理多个矩形应该很简单。
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Draggable Custom Painter',
home: Scaffold(
body: CustomPainterDraggable(),
),
);
}
}
class CustomPainterDraggable extends StatefulWidget {
@override
_CustomPainterDraggableState createState() => _CustomPainterDraggableState();
}
class _CustomPainterDraggableState extends State<CustomPainterDraggable> {
var xPos = 0.0;
var yPos = 0.0;
final width = 100.0;
final height = 100.0;
bool _dragging = false;
bool _insideRect(double x, double y) =>
x >= xPos && x <= xPos + width && y >= yPos && y <= yPos + height;
@override
Widget build(BuildContext context) {
return GestureDetector(
onPanStart: (details) => _dragging = _insideRect(
details.globalPosition.dx,
details.globalPosition.dy,
),
onPanEnd: (details) {
_dragging = false;
},
onPanUpdate: (details) {
if (_dragging) {
setState(() {
xPos += details.delta.dx;
yPos += details.delta.dy;
});
}
},
child: Container(
color: Colors.white,
child: CustomPaint(
painter: RectanglePainter(Rect.fromLTWH(xPos, yPos, width, height)),
child: Container(),
),
),
);
}
}
class RectanglePainter extends CustomPainter {
RectanglePainter(this.rect);
final Rect rect;
@override
void paint(Canvas canvas, Size size) {
canvas.drawRect(rect, Paint());
}
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}