Drag-and-Drop Support - The Definitive Guide to Java Swing - page 724

public interface Transferable{
public DataFlavor[] getTransferDataFlavors();
public boolean isDataFlavorSupported(DataFlavor);
public Object getTransferData(java.awt.datatransfer.DataFlavor)
throws UnsupportedFlavorException, IOException;
}
One common application for this is the ability to transfer images. The exposed property of
a JLabel or JButton is a javax.swing.Icon object, not a java.awt.Image object. While you can
certainly transfer Icon objects within and across Java programs, a more useful behavior is to
transfer Image objects to external entities, like Paint Shop Pro or Photoshop.
To create a transferable image object, the ImageSelection class, you must implement
the three Transferable interface methods and override four methods of TransferHandler :
getSourceActions() , canImport() , createTransferable() , and importData() .
■ Note The class for transferring strings is called StringSelection .
The getSourceActions() method needs to report which actions you are going to support.
By default, this is the TransferHandler.COPY operation when a property is set via the constructor, or
TransferHandler.NONE when it is not. Since the ImageSelection class implicitly uses the icon
property to get the component's image, just have the method return TransferHandler.COPY :
public int getSourceActions(JComponent c) {
return TransferHandler.COPY;
}
There is also a TransferHandler.MOVE operation, but you typically don't want the image to
be removed from the label it was copied from.
You pass the canImport() method a component and an array of DataFlavor objects. You
need to verify that the component is supported and one of the flavors in the array matches the
supported set:
private static final DataFlavor flavors[] = {DataFlavor.imageFlavor};
...
public boolean canImport(JComponent comp, DataFlavor flavor[]) {
if (!(comp instanceof JLabel) && !(comp instanceof AbstractButton)) {
return false;
}
for (int i=0, n=flavor.length; i<n; i++) {
for (int j=0, m=flavors.length; j<m; j++) {
if (flavor[i].equals(flavors[j])) {
return true;
}
}
}
return false;
}