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Identifiers (ids)

<Draggable /> > draggableId and <Droppable /> > droppableId

A <Draggable /> and a <Droppable /> have an id. These are draggableId and droppableId respectively.

String

We expect an id to be a string

type Id = string;
type DroppableId = Id;
type DraggableId = Id;

More information: types guide

Ids must be unique

A id must uniquely identify a <Draggable /> or <Droppable /> within a <DragDropContext />. So if you have multiple connected lists, each <Droppable /> needs to have a unique id and each <Draggable /> needs to have a unique id, even if the item is in a different list.

The id must also be unique even if the type argument on the <Droppable /> is different.

Ids must be a string

Right now it is important that all Id's be strings. rbd will throw an error if an Id is not a string.

Avoid reusing ids

For simplicity, it is best to avoid changing a draggableId or droppableId when a reorder occurs. The safest option is to associate an id with a piece of data and do not update the id between reorders.

You can change the draggableId or droppableId at any time except during a drag. Including after reorder. However, to avoid an exception you need to avoid reusing id's between two components. This can happen if you base a draggableId or droppableId on an index.

Don't base an id on a index

What this looks like internally

1. Update droppable

old droppableId: "droppable-0" new droppableId: "droppable-1"

👉 delete reference to "droppable-0" 👉 add reference to "droppable-1"

2. Update droppable

old droppableId: "droppable-1" 😢 new droppableId: "droppable-2"

👉 delete reference to "droppable-1" 😢 (will remove reference to our new "droppable-1") 👉 add a reference to "droppable-2"

3. Update droppable

old droppableId: "droppable-1" 💥 new droppableId: "droppable-5"

👉 delete reference to "droppable-1" 💥 (will cause an exception because "droppable-1" is not found)

Could we change these rules?

Yep!

But we do things this way for simplicity and performance. Feel free to continue this conversation in a Github issue if you feel strongly about it.

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