備忘録

title.rb

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: DragInAreaExample());
  }
}

class DragInAreaExample extends StatefulWidget {
  @override
  _DragInAreaExampleState createState() => _DragInAreaExampleState();
}

class _DragInAreaExampleState extends State<DragInAreaExample> {
  final GlobalKey _targetKey = GlobalKey();
  bool _dragStarted = false;

  void _checkIfInsideTarget(Offset globalPosition) {
    final RenderBox box = _targetKey.currentContext?.findRenderObject() as RenderBox;
    final Offset position = box.localToGlobal(Offset.zero);
    final Size size = box.size;

    final rect = Rect.fromLTWH(position.dx, position.dy, size.width, size.height);

    if (rect.contains(globalPosition) && !_dragStarted) {
      setState(() {
        _dragStarted = true;
      });
      print('ドラッグ開始（範囲内に入った）');
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Listener(
        onPointerMove: (event) {
          _checkIfInsideTarget(event.position);
        },
        onPointerUp: (_) {
          setState(() => _dragStarted = false);
        },
        child: Stack(
          children: [
            Center(
              child: Container(
                key: _targetKey,
                width: 200,
                height: 200,
                color: _dragStarted ? Colors.green : Colors.blue,
                child: Center(child: Text("この範囲にドラッグで入ってみて")),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

title.rb

void _checkIfInsideTarget(Offset globalPosition) {
  final RenderBox box = _targetKey.currentContext?.findRenderObject() as RenderBox;
  final Offset position = box.localToGlobal(Offset.zero);
  final Size size = box.size;

  final rect = Rect.fromLTWH(position.dx, position.dy, size.width, size.height);

  final isNowInside = rect.contains(globalPosition);

  if (isNowInside && !_dragStarted) {
    setState(() {
      _dragStarted = true;
    });
    print('枠内に入りました（ドラッグ開始）');
  } else if (!isNowInside && _dragStarted) {
    setState(() {
      _dragStarted = false;
    });
    print('枠から出ました（キャンセル）');
  }
}