Drag file "promises" (an unfortunately overridden word) are still a
little overly complex. I have ideas to address this in a future
release but some of the issues involved are... subtle. =) Here's a
link to documentation that should help you with understanding the
current model.
I'm very confused about drag promises and such. Another company
wants to send our app promised drags - the files are not actually
available until after our app says we'll accept the drag and the
mouse is released.
If their app adds kDragFlavorTypePromiseHFS, then our app gets that
and inspects the PromiseHFSFlavor struct that's in that drag item,
and we can accept the file based on that struct, we return noErr to
the kDragTrackingInWindow message.
Now what happens? Their app needs to add kDragFlavorTypeHFS,
otherwise our app will never get a file reference, right? Or is
something else supposed to happen?
You need to set the DropLocation so the sending application knows
where to place the newly minted file. Then you can call in their
promise to kDragFlavorTypeHFS to the the real file data.
Another part of the confusion is "promising" a drag flavor by
adding it with nil data. Which way is better, adding
kDragFlavorTypeHFS with nil data and setting the flavorDataPromised
flag, or to use kDragFlavorTypePromiseHFS with the PromiseHFSFlavor
struct?
The flavorDataPromised flag is set automatically by the system when a
flavor is promised with NULL data. Requesting both flavor types are
in the proper order is required for the full "promised file"
handshake to be complete. This is why things are a little complex.
Take a look at the documentation I provided above for more details.
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