Swing Hacks

Handle Dropped URLs #66

Chapter 9, Drag-and-Drop

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339

HACK

The constructor does all the work needed to accept drops. Really, this just

consists of creating a

DropTarget, which requires a Component (the “Drop

here” label), and a class implementing the

DropTargetListener

interface.

In the

drop( )

method, you need to

acceptDrop( )

to begin the process of

handling the drop. Pull out the

Transferable

from the

DropTargetDropEvent

,

and look to see if it supports any

DataFlavor

s that your application can sup-

port. In this demo, I implemented this with simple

if/else statements to try

the

urlFlavor and the constant stringFlavor. Each block knows what the

drop can be cast to, so one block casts to a

URL

, while the other casts to a

String.

When your code is finished handling the drop—successfully or not—you

need to call

dropComplete( ) on the DropTargetDropEvent, and pass a boolean

to indicate whether the drop was successful. The host OS can use this infor-

mation to finish animating the drop; for example, by flying the drag image

back to its source if the drop failed.

Drag Away

When you run the application, the big drop target is obvious, as seen in

Figure 9-2. In this case, a URL is being dragged from the Shiira web browser

on Mac OS X.

Once you drop a URL on the target, the dropped URL replaces the text in

the

JTextField (as seen in Figure 9-3).

Figure 9-2. Dragging a URL to a Swing component

Figure 9-3. Swing component after ...