可拖动的小部件不会落在确切的位置 Flutter

Question

我有一个这样的 Draggable。大多数教程视频是全屏使用 Draggable，但我只想在屏幕上的小区域使用它。

class DragBox extends StatefulWidget {
  final Offset initPos;
  final AssetImage image;

  DragBox(this.initPos, this.image);

  @override
  _DragBoxState createState() => _DragBoxState();
}

class _DragBoxState extends State<DragBox> {
  Offset position = Offset.zero;
  double top = 0;
  double left = 0;

  @override
  void initState() {
    super.initState();
    position = widget.initPos;
  }

  Widget _dragChild() {
    return CircleAvatar(
      backgroundImage: widget.image,
      backgroundColor: colorPlayerBackground,
    );
  }

  @override
  Widget build(BuildContext context) {
    return Positioned(
      left: position.dx,
      top: position.dy,
      child: Draggable(
        data: [widget.image],
        child: _dragChild(),
        onDraggableCanceled: (velocity, offset) {
          setState(() {
            position = offset;
          });
        },
        childWhenDragging: Opacity(
          opacity: 0.5,
          child: _dragChild(),
        ),
        feedback: _dragChild(),
      ),
    );
  }
}

在带有 DragTarget 的卡片容器内。

Container(
    width: double.infinity,
    child: Card(
      child: Stack(
        children: <Widget>[
          DragBox(Offset(0.0, 0.0), AssetImage(playerAnthonyMartial)),
          DragBox(Offset(150.0, 0.0), AssetImage(playerBrunoFernandes)),
          Positioned(
            left: 75.0,
            bottom: 0.0,
            child: Container(
              width: 120,
              height: 120,
              color: Colors.black,
              child: DragTarget(
                onWillAccept: (data) {
                  return true;
                },
                onAccept: (data) {
                  accept = true;
                },
                builder: (
                  BuildContext context,
                  List<dynamic> accepted,
                  rejected,
                ) {
                  return accept
                      ? Image.asset('assets/images/AnthonyMartial.png')
                      : Container();
                },
              ),
            ),
          )
        ],
      ),
    ),
  ),

但这会发生 when i drop it 这是怎么发生的，如何解决？

我按照 youtube 上的指南进行操作，但是当我将 Draggable 拖动到目标上时，似乎什么也没发生，数据是如何传递的。我完全不明白它是如何工作的。请帮忙！！！

Answer 1

如果不使用需要添加小偏移校正并移除卡。

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        body: SafeArea(
          child: MyHomePage(),
        ),
      ),
    );
  }
}

const playerAnthonyMartial = 'assets/AnthonyMartial.png';
const playerBrunoFernandes = 'assets/BrunoFernandes.png';
const colorPlayerBackground = Colors.white;

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    bool accept;
    return Stack(
      children: <Widget>[
        DragBox(Offset(0.0, 0.0), AssetImage(playerAnthonyMartial)),
        DragBox(Offset(150.0, 0.0), AssetImage(playerBrunoFernandes)),
        Positioned(
          left: 75.0,
          bottom: 0.0,
          child: Container(
            width: 120,
            height: 120,
            color: Colors.black,
            child: DragTarget(
              onWillAccept: (data) {
                return true;
              },
              onAccept: (data) {
                accept = true;
              },
              builder: (
                BuildContext context,
                List<dynamic> accepted,
                rejected,
              ) {
                return Container(child: Text('hey'));
              },
            ),
          ),
        )
      ],
    );
  }
}

class DragBox extends StatefulWidget {
  final Offset initPos;
  final AssetImage image;

  DragBox(this.initPos, this.image);

  @override
  _DragBoxState createState() => _DragBoxState();
}

class _DragBoxState extends State<DragBox> {
  Offset position = Offset.zero;
  double top = 0;
  double left = 0;

  @override
  void initState() {
    super.initState();
    position = widget.initPos;
  }

  Widget _dragChild() {
    return CircleAvatar(
      radius: 20,
      backgroundImage: widget.image,
      backgroundColor: colorPlayerBackground,
    );
  }

  @override
  Widget build(BuildContext context) {
    print(position);
    return Positioned(
      left: position.dx,
      top: position.dy,
      child: Draggable(
        data: [widget.image],
        child: _dragChild(),
        onDraggableCanceled: (velocity, offset) {
          setState(() {
            position = offset - Offset(0, 20);
          });
        },
        childWhenDragging: Opacity(
          opacity: 0.5,
          child: _dragChild(),
        ),
        feedback: _dragChild(),
      ),
    );
  }
}