Flutter 未调用 DragTarget onAccept

Question

I am developing a feature where the user enters a sentence, in the next screen the words of that sentence get shuffled randomly, then the user has to drag the words to a drag target to form the original sentence.

You can get an idea from the screenshots below.

First screen

Second screen

Now the problem I am having is, when dragging the words to the target I can see the DragTarget is calling onWillAccept as I added a print() statement there, if it is doing so then it should call onAccept eventually but it is not doing so. This is why my codes that deal with Bloc are not getting called and the words are not showing up in the target spot.

Code

class SentenceMakeScreen extends StatefulWidget {
  String inputSentence;

  SentenceMakeScreen(this.inputSentence);

  @override
  State<SentenceMakeScreen> createState() => _SentenceMakeScreenState();
}

class _SentenceMakeScreenState extends State<SentenceMakeScreen> {
  List<String> sentence = [];

  List<Widget> wordWidgets = [];
  
  bool isDragSuccessful = false;

  final ButtonStyle _buttonStyle = ElevatedButton.styleFrom(
      textStyle: TextStyle(fontSize: 20)
  );

  _getTextWidgets(List<String> sentence) {
    for(var i = 0; i < sentence.length; i++){
      wordWidgets.add(
        Draggable<WordWidget>(
         data: WordWidget(sentence[i]),
         child: WordWidget(sentence[i]),
         feedback: WordWidget(sentence[i]),
          childWhenDragging: Container(),
        )
      );
    }
  }

  _randomlyOrganizeSentence(String inputString) {
    sentence = inputString.split(new RegExp(r" "));
    sentence.shuffle();
    print(sentence);
  }

  @override
  void initState() {
    // TODO: implement initState
    _randomlyOrganizeSentence(widget.inputSentence);
    _getTextWidgets(sentence);
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    final _dragDropBloc = DragDropBloc();

    return Scaffold(
      appBar: AppBar(
        leading: IconButton(
          icon: Icon(Icons.arrow_back),
          onPressed: () {
            Navigator.pop(context);
          },
        ),
      ),
      body: Container(
        alignment: Alignment.center,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceAround,
          children: [
            DragTarget<WordWidget>(
              builder: (context, data, rejectedData) {
                return Center(
                  child: this.isDragSuccessful
                      ?
                  Container(
                    width: double.maxFinite,
                    margin: EdgeInsets.all(10),
                    decoration: BoxDecoration(
                      color: Colors.white,
                      border: Border(
                        bottom: BorderSide(width: 1.0, color: Colors.black),
                      ),
                    ),
                    child: StreamBuilder<List<WordWidget>>(
                      stream: _dragDropBloc.widgetStream,
                      initialData: [],
                      builder: (BuildContext context, AsyncSnapshot<List<WordWidget>> snapshot) {
                        print("Here ${snapshot.data}");
                        return Wrap(
                          direction: Axis.horizontal,
                          children: [
                            //correctly ordered words
                          ],
                        );
                      },
                    ),
                  )
                  :
                  Container(
                    width: double.maxFinite,
                    margin: EdgeInsets.all(10),
                    decoration: BoxDecoration(
                      color: Colors.white,
                      border: Border(
                        bottom: BorderSide(width: 1.0, color: Colors.black),
                      ),
                    ),
                    child: Text("Drag here")
                  ),
                );
              },
              onWillAccept: (data) {
                print("true");
                return true;
              },
              onAccept: (data) {
                print(data.toString());
                _dragDropBloc.dragDropEventSink.add(
                    DropEvent(WordWidget(data.toString()))
                );
                setState(() {
                  this.isDragSuccessful = true;
                  //draggedWords.add(data.toString());
                });
              },
            ),
            Wrap(
              direction: Axis.horizontal,
              children: wordWidgets
            ),
            Container(
              child: ElevatedButton(
                style: _buttonStyle,
                onPressed: () {

                },
                child: Text("Check"),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

WordWidget

import 'package:flutter/material.dart';

class WordWidget extends StatelessWidget {
  final String word;
  const WordWidget(this.word);

  @override
  Widget build(BuildContext context) {
    return Container(
      margin: EdgeInsets.all(10),
      decoration: BoxDecoration(
        color: Colors.red[900],
        border: Border.all(
            width: 4,
            color: Colors.black
        ),
        borderRadius: BorderRadius.circular(10),
      ),
      child: Padding(
          padding: EdgeInsets.all(5),
          child: Text(
            word,
            style: TextStyle(
                color: Colors.white
            ),
          )
      ),
    );
  }
}

I tried adding the type of data I am passing from Draggable to DragTarget , this is what was advised here . It did not work.

Answer 1

I was also getting the same error earlier today. I then upgraded my flutter to the latest version and wrote the DragTarget code again from scratch. I don't know what worked for me but you can try doing the same.