Swing Hacks

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Chapter 9, Drag-and-Drop

#67 Handle Dropped Images

HACK

drop( ) asks the Transferable for supported DataFlavors in the order you’d

prefer to deal with them. First, obviously, is

DataFlavor.imageFlavor. If this

is supported, you can trivially cast the data object returned by

Transferable.

getTransferData( )

to an Image.

The next easiest thing to deal with is the Java file list, denoted by the MIME

type

application/x-java-file-list, and handled by the DataFlavor constant

javaFileListFlavor. Given Swing’s support for various image file formats,

you can cast the transfer data to a

java.util.List, iterate over its members,

cast each one to a

File, and make an ImageIcon from each file’s path. URLs

work pretty much the same way: cast the transfer data to a

java.net.URL and

make an

ImageIcon from it.

URI lists take just a little work on your part. RFC 2483 defines these as

being some number of URIs, separated by CRLF pairs. It’s trivial to take the

URI list as a string and send it to a

StringTokenizer to pick out each URI,

which can then be passed to the

ImageIcon constructor.

Shut Up and Drag

Start up the demo and drag over an image from your favorite application, as

shown in Figure 9-4.

// url-lists are defined by rfc 2483 as crlf-delimited

StringTokenizer izer = new StringTokenizer (uris, "\r\n");

while (izer.hasMoreTokens ( )) {

String uri = izer.nextToken( );

System.out.println (uri);

ImageIcon icon = new ImageIcon (uri);

showImageInNewFrame (icon);

}

gotData = true;

} else if (trans.isDataFlavorSupported (urlFlavor)) {

System.out.println ("url flavor is supported");

URL url = (URL) trans.getTransferData (urlFlavor);

System.out.println (url.toString( ));

ImageIcon icon = new ImageIcon (url);

showImageInNewFrame (icon);

gotData = true;

}

} catch (Exception e) {

e.printStackTrace( );

} finally {

System.out.println ("gotData is " + gotData);

dtde.dropComplete (gotData);

}

}

Example 9-5. Handling the image drop (continued)