[news.eclipse.platform.swt] Re: DND with two different costum classes

[moritz.kreutzer@xxxxxx (Moritz Kreutzer)]

In Snippet 171 this is solved with two different DropTargets with one 
Transfer type per DropTarget. If I try to do this, I got an SWTError 
("Cannot initialize Drop"). I think, this is because I want to initialize 
multiple DropTargets on _one_ Control (a Tree=. (In the Snippets there are 
also multiple Controls.)
I also tried to implement validate() but this method seems to be never 
called.

Here is some sample code:

public class TreeDropTargetAdapter extends DropTargetAdapter {
 public void drop(DropTargetEvent event) {
   if 
(TreeParentTransfer.getInstance().isSupportedType(event.currentDataType)) {
     // add to tree and input
   } else if 
(TreeChildTransfer.getInstance().isSupportedType(event.currentDataType)) {
     // add...
   }
 }
}


//////////////////////////


public class TreeDragSourceAdapter extends DragSourceAdapter {
 public void dragSetData(DragSourceEvent event) {
   Object dragObj = 
((IStructuredSelection)treeViewer.getSelection()).getFirstElement();
   if (dragObj instanceof TreeParent)
     event.data = new TreeParent[] { (TreeParent) dragObj};
   else if (dragObj instanceof TreeChild)
     event.data = new TreeChild[] { (TreeChild) dragObj};
 }
}


//////////////////////////


public class TreeeView extends ViewPart {
 public void createPartControl(Composite parent) {
   DropTarget dt = new DropTarget(tree,DND.DROP_COPY | DND.DROP_MOVE | 
DND.DROP_DEFAULT);
   dt.setTransfer(new Transfer[] {TreeParentTransfer.getInstance(), 
TreeChildTransfer.getInstance() });
   dt.addDropListener(new TreeDropTargetAdapter());

   DragSource ds = ...

 }
} 


//////////////////////////


public class TreeParentTransfer extends ByteArrayTransfer {
 private static final String MYTYPENAME = "TREEPARENTTRANSFER";
 private static final int MYTYPEID = registerType(MYTYPENAME);
 private static TreeParentTransfer _instance = new TreeParentTransfer();

 private TreeParentTransfer() {
 }

 public static TemplateTransfer getInstance() {
   return _instance;
 }

 public void javaToNative(Object object, TransferData transferData) {
   if (!checkTemplate(object) || !isSupportedType(transferData)) {
     DND.error(DND.ERROR_INVALID_DATA);
   }
   // convert stuff
 }

 public Object nativeToJava(TransferData transferData) {
   if (!isSupportedType(transferData))
     return null;

   byte[] buffer = (byte[]) super.nativeToJava(transferData);
   if (buffer == null)
     return null;

   // convert stuff

   protected String[] getTypeNames() {
     return new String[] { MYTYPENAME };
   }

   protected int[] getTypeIds() {
     return new int[] { MYTYPEID };
   }

   private boolean checkTemplate(Object obj) {
     return (obj != null && obj instanceof TreeParent[]);
   }

   protected boolean validate(Object object) {
     return object instanceof TreeParent[];
   }
}


//////////////////////////


// same for TreeChild



I hope this will help you.

Regards, Moritz.