draggable_custom_painter.dart

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: DraggableCustomPainter(), ), ); } } class DraggableCustomPainter extends StatefulWidget { @override _DraggableCustomPainterState createState() => _DraggableCustomPainterState(); } class _DraggableCustomPainterState extends State<DraggableCustomPainter> { var xPos = 0.0; var yPos = 0.0; final width = 100.0; final height = 100.0; bool _dragging = false; /// Is the point (x, y) inside the rect? 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( 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; }