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Draggable

Draggable is the high-level drag source helper.

It takes a visible child and a payload of bytes. When the user begins dragging, the runtime carries those bytes until the drag is dropped onto a DragTarget or Dropzone. That payload is not your source of truth. It is only the message that travels during the drag.

Example​

use fission::prelude::*;

let node = Draggable {
payload: view.state.card_id.as_bytes().to_vec(),
on_drag_start: Some(start_drag_action),
on_drag_end: Some(end_drag_action),
child: Box::new(
    Button {
        child: Some(Box::new(Text::new("Release checklist").into_node())),
        on_press: Some(open_card_action),
        ..Default::default()
    }
    .into_node(),
),
}
.build(ctx, view);

The payload carries just enough information for the eventual drop target to know what moved. The actual board order, selection state, and persistence rules still belong in AppState and reducers.

Field table​

FieldTypeMeaningNotes / default behavior
payloadVec<u8>Bytes attached to the drag.Required. The reducer on the drop target decodes them from ctx.input.as_internal_drop().
childBox<Node>Visible content that the user drags.Required.
on_drag_startOption<ActionEnvelope>Action fired when dragging begins.Defaults to None. Useful for visual state such as highlighting the source item.
on_drag_endOption<ActionEnvelope>Action fired when dragging ends.Defaults to None, regardless of whether a target accepted the drop.

What belongs in app state and what belongs in the payload​

The payload should identify the thing being dragged. The app state should continue to own everything else: the actual collection order, which target is active, whether a drop is allowed, and what happens after acceptance.

This separation matters because it keeps drag-and-drop deterministic. Rebuilding the tree does not lose the product state, and tests can assert the reducer result without simulating hidden mutable widget internals.

Specific advice​

If you only need reordering inside one list, use a small stable id in the payload and let the reducer interpret it. If the dragged data is too large or too fragile to serialize to bytes comfortably, that is usually a sign that the payload is carrying too much product logic.

DragTarget, Dropzone, GestureDetector, and Button.