Why does not drag and drop work?!

Question

Hello,
I am trying to implent a drag and drop from a table to an icon representing a trash.
The drop handler fails in converting the selected rows to a list:
com.sun.el.MethodExpressionImpl@87d9c00d javax.el.ELException: java.lang.ClassCastException: java.lang.String cannot be cast to java.util.List
Could you help me to understand why? Below are the details.
This is the af:table:
<af:table var="row" rowBandingInterval="0" id="t1"
value="#{bindings.MyView1.collectionModel}"
rowSelection="multiple"
columnStretching="last"
horizontalGridVisible="false"
verticalGridVisible="false" fetchSize="-1"
autoHeightRows="6" width="190"
disableColumnReordering="true">
<af:column sortable="true" headerText="Entry" id="c1"
align="start">
<af:outputText value="#{row.Description}" id="ot1"/>
</af:column>
<af:dragSource actions="MOVE" defaultAction="MOVE"
discriminant="delete"/>
</af:table>
This is the drop area:
<af:image source="Images/empty_trash_32.png" id="i2">
<af:dropTarget dropListener="#{backingBeanScope.DropHandlerBean.dropHandler}"
actions="MOVE">
<af:dataFlavor flavorClass="org.apache.myfaces.trinidad.model.RowKeySet"
discriminant="delete"/>
</af:dropTarget>
</af:image>
This is the failing listener listener (the failing point is bold):
public DnDAction dropHandler(DropEvent dropEvent) {
DnDAction dnda = DnDAction.NONE;
if (dropEvent.getProposedAction() == DnDAction.MOVE) { // delete
RichTable table = (RichTable)dropEvent.getDragComponent();
//determine the rows that are dragged over
Transferable t = dropEvent.getTransferable();
//when looking for data, use the same discriminator as defined
//on the drag source
DataFlavor<RowKeySet> df =
DataFlavor.getDataFlavor(RowKeySet.class, "delete");
RowKeySet rks = t.getData(df);
if (rks == null) {
return DnDAction.NONE;
Iterator iter = rks.iterator();
while (iter.hasNext()) {
//get next selected row key
System.out.println(rks.toArray().length); // the number of selected rows is ok
List key = (List)iter.next(); // here gives: java.lang.ClassCastException: java.lang.String cannot be cast to java.util.List
//make row current so we can access it
table.setRowKey(key);
//the table model represents its row by the ADF binding class,
//which is JUCtrlHierNodeBinding
JUCtrlHierNodeBinding rowBinding =
(JUCtrlHierNodeBinding)table.getRowData();
Row row = (Row)rowBinding.getRow();
//delete row;
row.remove();
//activate animation
dnda = DnDAction.MOVE;
return dnda;
thanks.

Answer 1

I did try, I obtained this:
java.lang.NullPointerException
Why NullPointerException?
I don't know if this helps, but consider that the collection model comes from a ViewObject built on three EOs with many fields, although the table only shows one column.
This is the Iterator in my pageDef:
<table IterBinding="MyView1Iterator" id="MyView1">
<AttrNames>
<Item Value="Cod1"/>
<Item Value="Cod2"/>
<Item Value="Cod3"/>
<Item Value="Cod4"/>
<Item Value="Description"/>
<Item Value="Cod5"/>
</AttrNames>
</table>
Any idea?
I will see the Key content with the debugger.