public DropzoneState(Dropzone <TItem> dropzone)
 {
     this._dropzone = dropzone;
 }
 public DraggingFromCurrentZoneState(Dropzone <TItem> dropzone) : base(dropzone)
 {
 }
 public AvailableForDropState(Dropzone <TItem> dropzone) : base(dropzone)
 {
 }