[news.eclipse.platform.swt] Re: Dropping Java objects as text

[duongn@xxxxxxxxxx (Duong Nguyen)]

I'm a bit confused by your description but I'll try to answer this as best 
I can. In your first paragraph you indicated that you're serializing your 
object but in your second paragraph, you said that you reference the 
object directly for internal drops.

I don't think your proposed solution is right. You don't need to subclass 
TextTransfer to modify its behaviour. Doing so will prevent it from 
working with applications that expect a normal TextTransfer.

You can specify multiple transfer types from the drag source. One of the 
transfer type can be your internal transfer type as you have it now, and 
the second transfer type can be a TextTransfer type. The TextTransfer type 
may not have the complete data to reconstruct your actual object - it can 
simply be the "toString" equivalent of your object.

Depending on whether the drop target wants the actual object or the string 
description of the object, you will give him the right one in your 
dragSetData method.

To see an example of providing multiple transfer types, see Snippet185:
http://dev.eclipse.org/viewcvs/index.cgi/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet185.java?view=co

In your case, you would provide both the internal transfer type and the 
TextTransfer from your DragSource but you would only accept the internal 
transfer type from your DropTarget. The TextTransfer value would be for 
external applications such as NotePad.

I hope that helps.

Duong

David Huebel wrote:

> My application uses a TreeViewer to let users edit "bookmarks" and organize
> them in folders.  When users drag bookmarks and folders within the viewer,
> they are transferred as serialized objects using a subclass of
> ByteArrayTransfer.  This has been implemented and is working fine.  I want
> to be able to drag these same items *out* of the application so an external
> text representation can be dropped into other applications.

> I'm a bit stuck at this point.  The drop data can't be the external text
> representation because it wouldn't be appropriate for internal drops. 
> Currently the drop data is a reference to the object itself, which works
> fine for internal drops and seems like the right thing to do.  However,
> since the drop data isn't the external text representation, I can't use
> TextTransfer directly.  

> The natural thing to do seems to be to subclass TextTransfer and override
> javaToNative, but TextTransfer is designed to prevent subclassing -- it has
> no public or protected constructors. 

> I think I need to subclass ByteArrayTransfer (or Transfer) and implement
> getTypeNames() and getTypeIds() to return the same values as
> TextTransfer.getTypeNames() and TextTransfer.getTypeIds().  Where do I get
> these values?  I would like to delegate to the TextTransfer
> implementations, but they're protected.  I don't see any API in the dnd
> package that lets me retrieve the platform-specific names and IDs for
> dropping text.

> Am I going about this the right way?  What am I missing?  Any tips would be
> much appreciated.

> Thanks,
> David