你可以通过编程的方式把一个可拖拽对象放到一个拖拽目标里面吗?

Question

这个问题听起来很奇怪!但我有两个拖拽目标和两个拖拽对象。我要他们在每个目标都开一个枪。然后，当一个被拖放到第二个目标上时，第二个目标的可拖拽对象需要跳到第一个目标上。

我想问题的解决归结为你是否可以编程地把一个可拖动的目标。这看起来可能吗，还是DragTarget不合适?

一些示例代码-我不能在dragtargets

中启动draggables

import 'package:flutter/material.dart';
MyDraggable drag1 = new MyDraggable(Colors.red);
MyDraggable drag2 = new MyDraggable(Colors.green);
MyDragTarget target1 = new MyDragTarget();
MyDragTarget target2 = new MyDragTarget();
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData(fontFamily: 'PressStart'),
home: MyHomeScreen(),
);
}
}
class MyHomeScreen extends StatefulWidget {
MyHomeScreen({Key key}) : super(key: key);
createState() => MyHomeScreenState();
}
class MyHomeScreenState extends State<MyHomeScreen> {
@override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.red[100],
appBar: AppBar(
toolbarHeight: 70.0,
title: Center(child: Text('Swap the draggables')),
backgroundColor: Colors.pink,
),
body: Container(
color: Colors.yellow[200],
height: MediaQuery.of(context).size.height,
width: MediaQuery.of(context).size.width,
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: [
Center(
child: Row(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: [target1, drag1, drag2, target2],
// children: [target1, SizedBox(width: 100), target2],
),
),
Text('Q1: Can the Draggables be started in the DragTargets?'),
Text('Q2: If you drag from one target to the other, '
'can the second swap to the other target?'),
],
),
),
);
} // End build()
} // End class MyHomeScreenState
class MyDragTarget extends StatelessWidget {
bool dragAccepted = false;
Color acceptedColor;
@override
Widget build(BuildContext context) {
return Stack(children: [
Container(color: Colors.blue,height: 90.0,width: 90.0,
child: Padding(
padding: const EdgeInsets.all(20.0),
child: DragTarget<Color>(
builder: (context, List<Color> acceptedData, rejectedData) {
if (dragAccepted) {
return MyDraggable(acceptedColor);
} else {
return Container(color: Colors.grey,height: 50,width: 50,);
}
},
onWillAccept: (aColor) {
acceptedColor = aColor;
return true;
},
onMove: (moveData) {},
onAccept: (aColor) { dragAccepted = true; },
onLeave: (data) {},
),
),
),
]);
} // Build
} // End Class MyDragTarget
class MyDraggable extends StatefulWidget {
MyDraggable(this.color);
final Color color;
@override
_MyDraggableState createState() => _MyDraggableState();
}
class _MyDraggableState extends State<MyDraggable> {
@override
Widget build(BuildContext context) {
return Draggable(
data: widget.color,
child: Container(color: widget.color, height: 50, width: 50),
feedback: Container(color: widget.color, height: 50, width: 50),
childWhenDragging:
Container(color: Colors.pink[100], height: 50, width: 50),
onDragStarted: () {},
onDragEnd: (dragDetails) {
setState(() {});
},
onDragCompleted: () {},
onDraggableCanceled: (velocity, offset) {},
);
}
}

Answer 1

对于Flutter SDK中的默认Draggable，没有提供任何方法允许我们修改显示在UI上的Draggable的offset/position(所有这些信息都存储在Draggable的DraggableDetails中)。

话虽如此，有两个选项你可以尝试:

• 创建自定义Draggable类，允许以编程方式操纵其在UI上的位置
• 根据DragTarget类的onWillAccept回调(本例中为每个容器的color)更改Draggable小部件的子属性