我从 Flutter 开始,无法使用拖放功能。我遵循了文档,但不知道我做错了什么。
此示例应用程序显示三个正方形,蓝色是可拖动的。其他的都设置了 DragTarget,一个在方块内,一个在方块外。当我拖动蓝色方块时,它会打印拖动开始的信息,但在拖动目标上拖放时没有打印信息。
这是代码:
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.red,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Container(
constraints: BoxConstraints.expand(),
color: Colors.grey[900],
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Container(
width: 100,
height: 100,
color: Colors.red,
child: DragTarget(
onWillAccept: (d) => true,
onAccept: (d) => print("ACCEPT 1!"),
onLeave: (d) => print("LEAVE 1!"),
builder: (a,data,c) {
print(data);
return Center();
},
),
),
DragTarget(
onWillAccept: (d){return true;},
onAccept:(d) => print("ACCEPT 2!"),
onLeave: (d) => print("LEAVE 2!"),
builder: (context, candidateData, rejectedData){
return Container(
width: 150,
height: 150,
color: Colors.purple
);
}
),
Draggable(
data: ["SOME DATA"],
onDragStarted: () => print("DRAG START!"),
onDragCompleted: () => print("DRAG COMPLETED!"),
onDragEnd: (details) => print("DRAG ENDED!"),
onDraggableCanceled: (data, data2) => print("DRAG CANCELLED!"),
feedback: SizedBox(
width: 100,
height: 100,
child: Container(
margin: EdgeInsets.all(10),
color: Colors.green[800],
),
),
child: SizedBox(
width: 100,
height: 100,
child: Container(
margin: EdgeInsets.all(10),
color: Colors.blue[800],
),
),
),
],
)
),
)
);
}
}