Do I need to have data before performing Drag and Drop????

Question

I have gotten drag and drop working with Swing in JDK 1.4b2 using "URL-based" files instead of operating system native files. The way this was accomplished by creating a wrapper class that sub-classed File and would download the contents of the URL to a temporary file and then initiate a normal drag and drop operation using the normal java file mechanisms. However, when you have a large file, the operation can take too long since I am fronting all of the effort at the start of the drag. I would like to be able to delay the need to produce the bytes/files to give to the operating system until after there has been a successful drop, at which point I can do the heavy lifting and raise a dialog telling them that the action is commencing. As best as I can tell, you must have all of the data BEFORE any operation (which could be a potential design flaw!!)
So, is there a way to get a hook that there has been a successful drop to a vm-external drop target before the VM gives the data over? Even if I create my own data flavor (which isn't well documented outside of Text types) won't I still run into the same problems? Am I just overlooking something simple?
Thanks for your help.

Answer 1

Hello
I've had the same problem, but take a look at: http://foxtrot.sourceforge.net/
You can use their API to start the long consuming time job (reading files from the network) and also to paint a progress bar, showing the progress in the Event Dispatch Thread.
This is how I've solved my problem:
I've passed a MyTransferable object to the startDrag method of the DragGestureEvent event.
In the getTransferData method of MyTransferable object (that implements Transferable interface) I've used the Worker.post method of their API which reads the file from the network and updates a progress bar.
The API lets the Event Dispatch Thread enter but not return from the listener method (getTransferData in my case), instead rerouting the Event Dispatch Thread to continue dequeuing events from the Event Queue and processing them (repaint the progress bar). Once the worker thread has finished, the Event Dispatch Thread is rerouted again, returning from the listener method.