React beautiful DND - I get "Unable to find draggable with id: 1"

Question

In the code below the UI renders two "Column" components and each column contains two draggable elements called "Tasks". When the user drags a "Task" between columns the code works - up to a point. When the user continuously drags the task components around eventually they will stop dragging and the user gets an error that says:

Unable to find draggable with id: X

I don't know why this happens nor how to fix it.

Note: I am assuming the way the library works is when you drag elements you need to reorder and update your state in the onDragEnd function.

Here is my code:

app.js

import React,{useState} from 'react';
import {DragDropContext} from 'react-beautiful-dnd';
import helper from './helper_functions'

import Column from './Components/Column';

function App() {

  let initialState =   [
    {
      groupName:"Today",
      tasks:[
          {id:"1", title:"Test-1"},
          {id:"2", title:"Test-2"}
        ]
    },
    {
      groupName:"Tomorrow", 
      tasks:[
          {id:"3", title:"Test-3"},
          {id:"4", title:"Test-4"}
        ]
    },
  ]


  const [taskList, setTasks] = useState(initialState)

  function onDragEnd(val){

     let result = helper.reorder(val.source,val.destination,taskList);
     setTasks(result)
  }

  return (
    <DragDropContext onDragEnd={onDragEnd}>
       <Column droppableId="Today" list= {taskList[0].tasks} type="TASK"/>
       <Column droppableId ="Tomorrow" list = {taskList[1].tasks} type="TASK"/>
       <div> context hello world </div>
    </DragDropContext>
  );
}

export default App;

src/helper_functions

export default {
    reorder:function(source,destination,taskDataArr){

     let taskData = [...taskDataArr]

 //     //_____________________________________________________________Source data
    let sourceGroupIndex = taskData.findIndex((val, index) => {                // iterate and find "Today" (or other) index in list data
        return val.groupName === source.droppableId
    });

    let draggedTask = taskData[sourceGroupIndex].tasks.find((val, index) => {  // Get specific task object based on index
        return source.index === index
    }); // dragged object

    let sourceListCopyWithElementRemoved = taskData[sourceGroupIndex].tasks.filter((val, index) => {
        return index !== source.index // removes dragged element from array
    });

    // //__________________________________________________________________Destination data

    let destinationGroupIndex = taskData.findIndex((val, index) => {  // iterate and find "Tomorrow" (or other) index in list data
        return val.groupName === destination.droppableId
    });


    taskData[destinationGroupIndex].tasks.splice(destination.index, 0, draggedTask); // insert dragged item to new place
    taskData[sourceGroupIndex].tasks = sourceListCopyWithElementRemoved

    return taskData

  }


}

src/Components/Column

import React from 'react';
import {Droppable} from 'react-beautiful-dnd';
import Task from "../../Components/Task"

function Column(props){
   const { classes, droppableId, list, type} = props;

   let style = {
    backgroundColor:"orange",
    height:"300px",
    width:"400px",
    margin:"100px"

   }

   console.log(list)



    return (

       <Droppable droppableId = {droppableId} type={type}>
       {provided => (

          <div {...provided.droppableProps} ref={provided.innerRef} style={style}>
          <h2>{droppableId}</h2>

            {list.map((val,index)=>{
               return <Task id={val.id} key={index} index={index} title={val.title}/>
            })}

           {provided.placeholder}
          </div>
        )
       }
       </Droppable>
    )
}

export default Column

src/Components/Task

import React from 'react';
import {Draggable} from 'react-beautiful-dnd';



function Task(props){
    const { classes, id, index,title } = props;
    let style = {
    backgroundColor:"red",


   }

    return (
       <Draggable draggableId ={id} index={index} type="TASK">

         {(provided) => (
            <div
              ref={provided.innerRef}
              {...provided.draggableProps}
              {...provided.dragHandleProps}
            >
              <h4 style={style}>{title}</h4>
            </div>
        )}

       </Draggable>
    )
}

export default Task

Answer 1

There are a few issues with your code:

1. Error Unable to find draggable with id: X

In the Column component you used index as a key for the tasks. I think this is what causes this error.

Using the task id as key, in Column, makes this error go away.

2. reorder has some issues:
   • it removes a task when dropped in the same column
   • raises an error when a task is dropped outside the columns

I had a bit of fun with you code and tried another way to reorder. This way of reordering might come in handy if you ever add a more columns - there is still room for improvements.

Hope it helps!