Thread Subject: Java drag & drop

Here are two attempts to implement drop & drag. The second
method is successful in invoking the callback, but access
to hObj and EventData (e,g, through get) then cause
exceptions. Does anyone (are you there Yair) have any ideas?

function droptrial()
f=figure();
j=javacomponent('javax.swing.JComboBox',[],f);
j.setEditable(true);
e=get(j.Editor,'EditorComponent');

% METHOD 1
% This produces an exception and fails:
dnd=e.getDropTarget();
set(dnd, 'DropCallback', @MyCallback);

% METHOD 2
% This works but calls like get(hObj) produce exceptions in
the callback
dnd=java.awt.dnd.DropTarget();
set(dnd, 'DropCallback', @MyCallback);
e.setDropTarget(dnd);
return
end

function MyCallback(hObj, Ev)
get(hObj);
return
end

METHOD1 produces
java.lang.IllegalAccessException: Class
com.mathworks.jmi.bean.MatlabBeanInterface can not access a
member of class javax.swing.TransferHandler$SwingDropTarget
with modifiers "public"
at sun.reflect.Reflection.ensureMemberAccess
(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at
com.mathworks.jmi.bean.MatlabBeanInterface.addCallback
(MatlabBeanInterface.java:691)
at
com.mathworks.jmi.bean.MatlabCallbackInterface.addCallback
(MatlabCallbackInterface.java:128)


METHOD2, when get(hObj) is called from the callback after
making a drop (from a JTree) produces
K>> get(hObj)
Active = on
Class = [ (1 by 1) java.lang.Class array]
Component = [ (1 by 1)
javax.swing.plaf.metal.MetalComboBoxEditor$1 array]
DefaultActions = [3]
DropTargetContext = [ (1 by 1)
java.awt.dnd.DropTargetContext array]
FlavorMap = [ (1 by 1)
java.awt.datatransfer.SystemFlavorMap array]
DropCallback = [ (1 by 1) function_handle array]
DropCallbackDatajava.lang.reflect.InvocationTargetEx
ception
at sun.reflect.NativeMethodAccessorImpl.invoke0
(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke
(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke
(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.mathworks.jmi.bean.ClassInfo.getObjectField
(ClassInfo.java:323)
Caused by: java.awt.dnd.InvalidDnDOperationException: The
operation requested cannot be performed by the DnD system
since it is not in the appropriate state
at java.awt.dnd.DropTargetContext.getTransferable
(Unknown Source)
at java.awt.dnd.DropTargetDropEvent.getTransferable
(Unknown Source)
... 5 more

I must admit I'm just as baffled. It appears that
e.setDropTarget() overrides the default call to the drop
target's TransferHandler() method (which is the default text
handler
javax.swing.plaf.basic.BasicTextUI$TextTransferHandler). You
might try to implement your own TransferHandler as explained
here:
http://java.sun.com/docs/books/tutorial/uiswing/dnd/intro.html
. I believe R2007b (Matlab 7.5) uses Java 1.6 and if so,
then you may be interested in the following article:
http://weblogs.java.net/blog/shan_man/archive/2006/02/choosing_the_dr.html

Yair Altman
http://ymasoftware.com

Dear Yair
Many thanks.
The R2007b pre-release produces identical exceptions but
thanks for the links. I think your suggestion is on the
right lines: the problems in the callback seem to arise
through calls to DropTargetDropEvent.getTransferable().
I'll follow the links and try TMW with a service request.
ML

I've posted a drag and drop example, but using Activex.

http://www.mathworks.com/matlabcentral/fileexchange/loadFile
.do?objectId=16312&objectType=file

<a
href="http://www.mathworks.com/matlabcentral/fileexchange/lo
adFile.do?objectId=16312&objectType=file">
http://www.mathworks.com/matlabcentral/fileexchange/loadFile
.do?objectId=16312&objectType=file </a>

Thanks Raphael. Unfortunately, I need a platform-
independent method.

For those interested TMW Support have just sent this to
Development as a bug notice.

I have found a workaround for my specific needs but not a
proper one. Might the drop event have been handled/rejected
in a listener before the callback is activated?

I should have added:

dnd=java.awt.dnd.DropTarget();
dnd=handle(dnd,'callbackProperties')

at least lets you get(hObject) in the callback as long as
you do not call hObject.getTransferable()