Swing Hacks

336

|

Chapter 9, Drag-and-Drop

#66 Handle Dropped URLs

HACK

H A C K

#66

Handle Dropped URLs

Hack #66

Drag-and-drop is like a box of chocolates; you never know what you’re going

to get....

Bookmark menus are so 1995. Today, you should expect to be able to drag

URLs to other applications and have those applications open web pages,

store the address in a bookmark database, start an email in response to a

mailto: URL, etc. Java’s networking chops are well-established and aren’t

the problem here. The issue is actually getting the URL itself from the drop.

To accept drops of native objects, your GUI needs to designate some

Component as the onscreen drop target. Your code then implements the

DropTarget

interface, which means your implementation will get callbacks

when the user drags the mouse into your component, over it, out of it, etc.

Most of

DropTarget’s methods can be left as no-ops; for now, only the drop( )

method matters.

What’s interesting about native drag-and-drop (and copy-and-paste, for that

matter) is that there’s not necessarily one way to represent the data being

transferred. Instead, you do a sort of negotiation with the

Transferable

passed to you by the DropTargetDropEvent: it specifies, in order of robust-

ness, which

DataFlavors it can deliver, or you ask whether specific

DataFlavors are supported.

In the demo code in Example 9-3, I have a method called

dumpDataFlavors( ),

which shows the

DataFlavor ...