Swing Hacks

Handle Dropped Images #67

Chapter 9, Drag-and-Drop

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341

HACK

The first thing you should notice is the poor support for dragging and drop-

ping images in Windows: Paint, Picture and Fax Viewer, and the Quick-

Time applications are not drag sources, and dragging an image from the

playlist of Windows Media Player to the Swing application in this hack actu-

ally crashes Java.

Furthermore, the supported

DataFlavor

s are all over the map. A lot of these

provide references to image files in the form of either a

javaFileListFlavor

(as do the Windows and Mac desktops), a list of URIs (the MIME type text/

uri-list

defined by RFC 2483 and supported by many of the browsers), or a

single URL. To top it off, some of the older Mac applications send a single,

hard-to-handle

DataFlavor that will require special QuickTime-based

handling

[Hack #68].

Thanks to Swing’s support for common image types like GIF, JPEG, and

PNG, a file reference is good enough because you can easily make an

ImageIcon from a URL or filepath to any of these types.

Grabbing the Drop

Example 9-4 shows a basic application that accepts a drop and tries to

obtain from the drop (in order of preference):

1. A

java.awt.Image

2. A java.util.List of java.io.Files

3. A

String, formatted per the uri-list spec

4. A

java.net.URL

Example 9-4. Handling dropped images from other applications

public class ImageDropTargetDemo extends JPanel

implements DropTargetListener {

DropTarget ...