reparenting.md

<Draggable /> の親子化

ドラッグ中に、ドラッグしているアイテムの親エレメントを変更したい場合があります。これには2つのアプローチがあります:

1. 第 1 種クローン API を使用する（仮想リストに必要）
2. ReactDOM.createPortal を使って独自の portal を使用する

バックグラウンド

We leave elements in place when dragging. We apply position: fixed on elements when we are moving them around. This is quite robust and allows for you to have position: relative | absolute | fixed parents. However, unfortunately position:fixed is impacted by transform (such as transform: rotate(10deg);). This means that if you have a transform: * on one of the parents of a <Draggable /> then the positioning logic will be incorrect while dragging. Lame! For most consumers this will not be an issue.

To get around this issue you need to move the dragging item to another location in the DOM - usually document.body or a direct descendent of it. This removes the impact of any parent styles on the position:fixed. The new parent is often referred to as a portal.

Cloning API

Our cloning API is a first class way of reparenting a <Draggable />s into another DOM location while a drag is occurring. When using our cloning API the original <Draggable /> is removed while the drag is being performed; a new clone is rendered (using renderClone) into the container element (controllable using getContainerForClone)

Generally you will want to render the same visual item as the one that is dragging, but you can render anything you want. The displacement will be based on the dimensions of the original item so we strongly recommend using an element that is exactly the same size.

Using our cloning API is required for compatibility with virtual lists.

function List(props) {
  const items = props.items;

  return (
    <Droppable
      droppableId="droppable"
      renderClone={(provided, snapshot, rubric) => (
        <div
          {...provided.draggableProps}
          {...provided.dragHandleProps}
          ref={provided.innerRef}
        >
          Item id: {items[rubric.source.index].id}
        </div>
      )}
    >
      {provided => (
        <div ref={provided.innerRef} {...provided.droppableProps}>
          {items.map((item) => (
            <Draggable draggableId={item.id} index={item.index}>
              {(provided, snapshot) => (
                <div
                  {...provided.draggableProps}
                  {...provided.dragHandleProps}
                  ref={provided.innerRef}
                >
                  Item id: {item.id}
                </div>
              )}
            </Draggable>
          ))}
        </div>
      )}
    </Droppable>
  );
}

You can also reuse the <Draggable /> | DraggableChildrenFn if you want too!

const getRenderItem = (items) => (provided, snapshot, rubric) => (
  <div
    {...provided.draggableProps}
    {...provided.dragHandleProps}
    ref={provided.innerRef}
  >
    Item id: {items[rubric.source.index].id}
  </div>
);

function List(props) {
  const items = props.items;
  const renderItem = getRenderItem(items);

  return (
    <Droppable
      droppableId="droppable"
      renderClone={renderItem}
    >
      {(provided, snapshot) => (
        <div ref={provided.innerRef} {...provided.droppableProps}>
          {items.map((item) => (
            <Draggable draggableId={item.id} index={item.index}>
              {renderItem}
            </Draggable>
          ))}
        </div>
      )}
    </Droppable>
  );
}

<Droppable /> | renderClone

This function is called to get a clone to be rendered while dragging.

renderClone: ?DraggableChildrenFn

type DraggableChildrenFn = (
  Provided,
  StateSnapshot,
  DraggableRubric,
) => Node | null;

This is the same type as the child function for a <Draggable />. See <Draggable /> for more details.

<Droppable /> | getContainerForClone

A function that is called to get the DOM element you would like to put the clone into. If function is not defined, then document.body is used

getContainerForClone: () => HTMLElement,

Rolling your own portal

⚠️ You are welcome to use your own portal solution if you want to from within your <Draggable />. Before we had a cloning API, reparenting needed to be done by using your own portal. It is now recommended that you use the cloning API.

We have created a working example that uses ReactDOM.createPortal directly to guide you. You can view the source here.

If you are doing drag and drop reordering within a <table> we have created a portal section inside our table guide

パフォーマンス ⚠️

Keep in mind that anything that is reparented will be rendered from scratch. So you do not want to be moving large component trees into a portal: otherwise you will experience large UI jank. We do not recommend using reparenting out of the box because of this performance drawback.

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