Swing Hacks

Handling Dropped Picts on Mac OS X #68

Chapter 9, Drag-and-Drop

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349

HACK

Next is the QTJ stuff. It’s OK if you don’t totally understand it—QTJ code

is pretty twisted. That’s why there’s a whole book on it. First, you open a

QTSession

, which initializes QuickTime and allocates resources. You have to

do this before any QTJ call. It can throw a

QTException

, as can most other

QTJ calls, so the whole thing is wrapped in a

try

-

catch

block.

Next, you create a

Pict

object from the byte array and pass that to

DataRef

,

which is a sort of generic media reference. In this case, you pass in flags to tell

the

DataRef exactly what it’s pointing to. The second and third arguments

indicate that we’re using the old-style Mac OS file type and that its value is

PICT. You might be wondering why being a Pict object isn’t self-descriptive

enough. It’s because many QTJ objects are just pointers to blocks of memory

and the functions that work with them. The

DataRef signature used here

takes a

QTHandleRef as an argument. QTHandleRef is subclassed by Pict, but it

is little more than a pointer; the only level on which the

DataRef understands

the

Pict, in fact, is as a block of memory. My point here: QTJ code is weird

and often C-like.

Create a

GraphicsImporter for the Pict format, and point it to the DataRef.

You have now read the Pict “file” from memory. Now, you can get the size

of the imported image and create a

QTImageProducer, with help from a

GraphicsImporterDrawer (a sort of QT-to-Java bridge for still images, also

used by QTJ’s Swing

JComponents). Since this is a normal, everyday

ImageProducer, you can create an image with Component.createImage( ) or

Toolkit.createImage( ).

Finally, you need to call

QTSession.close( ) to deallocate QuickTime

resources. It’s OK to do it many times in a program, although it’s probably

more efficient to

open( ) it once and close( ) it once; e.g., in your quit han-

dler or a shut-down hook.

Take a Breath and Run

The code works exactly as in the previous hack—all you’ve done is support

one more

DataFlavor. In Figure 9-6, I’ve dropped two images from Quick-

Time Player onto the Java app, and both are shown in their own windows.

Actually, this is a little more interesting than it looks because the larger

image isn’t a still image; it’s the current frame of an MPEG-4 movie that I

dragged and dropped into the Java app. The single frame is transported as a

Pict, and using QTJ lets you get it into the Java world. This hack only

scratches the surface of QTJ’s potential—if you want to do Java Media on

the Mac, you should check out QuickTime for Java: A Developer’s Note-

book, by Chris Adamson (yours truly), published by O’Reilly.