A visual element that is draggable.

Draggable.cs

using UnityEngine;
using UnityEngine.Scripting;
using UnityEngine.UIElements;

/** A visual element that is draggable. Good example of using the
    VisualElement's `tranform.position`.

    Credit to Crayz for their code:

    https://forum.unity.com/threads/creating-draggable-visualelement-and-clamping-it-to-screen.1017715/
*/
public class Draggable : VisualElement {
  internal Vector3 offset;
  private bool isDragging = false;

  public Draggable() {
    RegisterCallback<PointerDownEvent>(DragBegin);
    RegisterCallback<PointerUpEvent>(DragEnd);
    RegisterCallback<PointerLeaveEvent>(DragEndOnLeave);
    RegisterCallback<PointerMoveEvent>(PointerMove);
  }

  public void DragBegin(PointerDownEvent ev) {
    isDragging = true;
    offset = ev.localPosition;
    ev.target.CapturePointer(ev.pointerId);
  }

  private void DragEnd(PointerUpEvent ev) {
    ev.target.ReleasePointer(ev.pointerId);
    isDragging = false;
  }

  private void DragEndOnLeave(PointerLeaveEvent ev) {
    ev.target.ReleasePointer(ev.pointerId);
    isDragging = false;
  }

  private void PointerMove(PointerMoveEvent ev) {
    if (isDragging) {
      Vector3 delta = ev.localPosition - (Vector3) offset;
      transform.position = transform.position + delta;
    }
  }


  [Preserve]
  public new class UxmlFactory : UxmlFactory<Draggable, UxmlTraits> { }

  [Preserve]
  public new class UxmlTraits : VisualElement.UxmlTraits { }

}