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我需要在里面找到可拖动的位置DragTarget.onMove。但是DragTargetDetails.offset我们有一些奇怪的价值观。在源代码中,我看到它设置为avatar._lastOffsetwhich is globalPosition - dragStartPoint。但是我无权访问其中任何一个来计算 DragTarget 中的全局位置或本地位置。文档说DragTargetDetails.offset是“在可拖动对象上发生特定指针事件时的全局位置。” 但实际上它是一个全局位置减去开始用药点,这似乎没用,我该如何使用该值?

我准备了一个简单的示例,您可以在其中看到偏移量Draggable.onDragUpdate(这是真正的全局位置)和DragTarget.onMove.


import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);
  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Offset _dragUpdateOffset = Offset.zero;
  Offset _moveOffset = Offset.zero;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Draggable(
          data: "Test Data",
          child: const Text("Drag me"),
          feedback: const Material(child:Text("Draggable")),
          childWhenDragging: Container(),
          onDragUpdate: (details) {
            setState(() {
              _dragUpdateOffset = details.globalPosition;
            });
          },
        ),
      ),
      body: Column(
        children: [
          Row(
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: [
            Text("dragUpdate: ${_dragUpdateOffset.dx},${_dragUpdateOffset.dy}"),
            const Text("vs"),
            Text("onMove: ${_moveOffset.dx},${_moveOffset.dy}")
          ],),
          Expanded(
            child: Center(
              child: DragTarget(
                onMove: (details) {
                  _moveOffset = details.offset;
                },
                onWillAccept: (data) => true,
                builder: (context, candidateData, rejectedData) => SizedBox(
                  width: 100,
                  height: 100,
                  child: Container(
                    child: const Text("DragTarget"),
                    decoration: const BoxDecoration(color: Colors.green),
                  ),
                ),
              ),
            ),
          ),
        ],
      ),
    );
  }
}
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1 回答 1

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尝试使用 Listener 包装 Draggable 并使用“onPointerMove: (details)”。

于 2021-09-17T13:31:08.410 回答