Flutter DragTarget on hover

Question

When exploring the Flutter's DragTarget class I could not find any mechanism to hook to the 'on hover event' if you will. Here is an example:

 class DropZone extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Container(
      height: 40,
      color: Colors.green,
      child: DragTarget(
          builder: (context, List<int> candidateData, rejectedData) {
            print("dragged");
            return new Container(color: Colors.red,);
          },
      onWillAccept: (data) {
            return true;
      },),
    );
  }
}

I would like to change the color of the container when a Draggable object is hovered but not yet dropped. The builder method, in this case, only executes during the initial rendering and when the Draggable leaves the target. I suspect I have to do something in the onWillAccept method but not sure what. Does anybody have a solution?

are you using the positioned widget?

flutter
– flutter

2018-12-30 21:28:11 +00:00
Commented Dec 30, 2018 at 21:28 — flutter
– flutter, Commented Dec 30, 2018 at 21:28

flutter · Accepted Answer · 2018-12-30 21:35:50Z

here is the code for what I think you're looking for

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: App(),
      ),
    );
  }
}

class App extends StatefulWidget {
  @override
  _AppState createState() => _AppState();
}

class _AppState extends State<App> {
  Color caughtColor = Colors.grey;
  @override
  Widget build(BuildContext context) {
    return Stack(
      children: <Widget>[
        DragBox(Offset(0.0, 0.0), Colors.green),
        Positioned(
            left: 100,
            bottom: 0.0,
            child: DragTarget(onAccept: (Color color) {
              caughtColor = color;
            }, builder: (
              BuildContext context,
              List<dynamic> accepted,
              List<dynamic> rejected,
            ) {
              return Container(
                width: 200,
                height: 200,
                color: accepted.isEmpty ? caughtColor : Colors.grey.shade200,
              );
            }))
      ],
    );
  }
}

class DragBox extends StatefulWidget {
  final Offset initPos;
  final Color itemColor;

  DragBox(this.initPos, this.itemColor);
  @override
  _DragBoxState createState() => _DragBoxState();
}

class _DragBoxState extends State<DragBox> {
  Offset position = Offset(0.0, 0.0);

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

  @override
  Widget build(BuildContext context) {
    return Positioned(
      left: position.dx,
      top: position.dy,
      child: Draggable(
        data: widget.itemColor,
        child: Container(
          width: 100,
          height: 100,
          color: widget.itemColor,
        ),
        onDraggableCanceled: (velocity, offset) {
          setState(() {
            position = offset;
          });
        },
        feedback: Container(
          width: 120,
          height: 120,
          color: widget.itemColor.withOpacity(0.5),
        ),
      ),
    );
  }
}

Daniel Z. · Accepted Answer · 2022-07-11 22:24:03Z

3

You can use the candidateData parameter in the DragTarget.builder:

...
border: Border.all(
           color: candidateData.isNotEmpty
            ? Colors.red
            : Colors.black)),

The code above changes the border color to red upon hover.

answered Jul 11, 2022 at 22:24

Daniel Z.

958 bronze badges

1 Comment

Community Over a year ago

As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.

Akash · Accepted Answer · 2022-06-08 12:10:59Z

You can make combination of onAccept, onMove and onLeave functions in DragTarget to achieve the result.

Here is how you do it:

// ...
bool isTargetGettingDroppedForDelete = false;
//...

DragTarget<String>(
        builder: (
          BuildContext context,
          List<dynamic> accepted,
          List<dynamic> rejected,
        ) {
          return Container(
            height: 100,
            width: 100,
            color: isTargetGettingDroppedForDelete ? Colors.red : Colors.green,
          );
        },
        onWillAccept: (data) {
          return data == Constants.draggable;
        },
        onAccept: (data) {
          setState(() {
            isTargetGettingDroppedForDelete = false;
          });
        },
        onMove: (details) {
          setState(() {
            isTargetGettingDroppedForDelete = true;
          });
        },
        onLeave: (data) {
          setState(() {
            isTargetGettingDroppedForDelete = false;
          });
        },
      ),

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