Using the Transfer Callback

The transfer callback accepts data from the drag source when a drop occurs. The first action in the transfer callback is a verification of the reason field in the callData. If the reason is not DtCR_DND_TRANSFER_DATA, you should return immediately; otherwise, proceed with data transfer based on its type and the operation specified in the reason. For example, if you are handling the copy of a file, retrieve the file name from the data structure, open the file, and copy its contents. If your drop zone supports more than one data type, you need to support the transfer of each data type appropriately.

Here is a simple transfer callback for a drawing area drop zone that supports the copying of text and file-name data types.

void
	TransferCallback(
 	Widget widget,
 	XtPointer clientData,
 	XtPointer callData)
{
   DtDndTransferCallbackStruct *transferInfo =
				(DtDndTransferCallbackStruct*) callData;
   int ii;

   DtDndcontext * dropData = transferInfo->dropData;
 			return;
   switch dropData->protocol {
 	case DtDND_FILENAME_TRANSFER:
 		for (ii=0; ii < dropData->numItems; ii++) {
 			drawTheString(dropData->data, strings[ii]);
 		}
 		break;
 	case DtDND_TEXT_TRANSFER:
 		for (ii=0; ii<dropData->numItems; ii++){
      drawTheFile(dropData->data.files[ii]);
 		}
      break;
 	default:
			transferInfo->status = DtDND_FAILURE;
     }
}