The document describes steps to customize the GMF drag-and-drop framework. It involves contributing a custom edit policy provider, attaching a custom edit policy and drop target listener to edit parts, preparing dropped objects, finding a target edit part, returning commands from edit parts, and executing drag-and-drop commands to create concepts through generators.

1. Customizing GMF DnD Framework
Step 1 : Contributing custom edit policy provider to GMF editor
In our DnD handler plugin, we contribute
com.tibco.xpd.cm.boma.dnd.core.BOMADnDEditPolicyProvider to the
org.eclipse.gmf.runtime.diagram.ui.editpolicyProviders.
This Presentation Edit Policy Provider extension point is used to define editpolicy providers
for the editpolicy service.
The editpolicy service allows plug-ins to modify or enhance the behavior of an editpart via an
editpolicy without modifying the editpart code.
Step 2 : Attach a custom edit policy and a drop target listener to the edit part
public void createEditPolicies(EditPart editPart) {
if (isEditPartValid(editPart)) {
/** if the edit part is valid,
install the dnd edit policy
editPart.installEditPolicy(EditPolicyRoles.DRAG_DROP_ROLE,
dndPolicy);
editPart.getViewer().addDropTargetListener(dndListner);
**/
}
}
public boolean provides(IOperation operation) {
if(operation instanceof CreateEditPoliciesOperation){
EditPart editPart =
((CreateEditPoliciesOperation)
operation).getEditPart();
return isEditPartValid(editPart);
}
return false;
// Custom Edit Policy
public class BOMADragDropEditPolicy extends DragDropEditPolicy {
//------
}
Step 3 : Prepare the list of objects to be dropped and set it on the Drop Request
@Override
protected List<Object> getObjectsBeingDropped() {
ISelection selection =

2. LocalSelectionTransfer.getInstance().getSelection();
if (selection instanceof IStructuredSelection) {
sourceObjectList =
((IStructuredSelection) selection).toList();
}
return sourceObjectList;
}
@Override
protected Request createTargetRequest() {
DropObjectsRequest req = new DropObjectsRequest();
req.setObjects(getObjectsBeingDropped());
return req;
}
Step 4: Return an edit part that can produce an executable command for the
target request
private EditPart calculateTargetEditPart() {
updateTargetRequest();
EditPart ep = getViewer()
.findObjectAtExcluding(
getDropLocation(),
getExclusionSet(),
new
EditPartViewer.Conditional() {
public
boolean evaluate(EditPart editpart) {
Command command =
editpart.getCommand(getTargetRequest());
return command != null;
}
});
/*if (ep != null) {
Command command =
ep.getCommand(getTargetRequest());
return (command != null &&
command.canExecute())? ep : null;
}*/
return ep;
}
Step 5: Return the required DnD command from the corresponding Edit Part
/**
* @generated NOT
*/
@Override
public Command getCommand(Request _request) {
if(_request instanceof DropObjectsRequest)
{

3. return
getDnDEditPolicy().getCommand(_request);
}else {
return
super.getCommand(_request);
}
}
/**
* @generated NOT
* @return
*/
private EditPolicy getDnDEditPolicy() {
EditPolicy dndPolicy = null;
EditPolicyIterator i =
getEditPolicyIterator();
while (i.hasNext()) {
EditPolicy tempPolicy =
i.next();
if (tempPolicy instanceof
DragDropEditPolicy) {
dndPolicy =
tempPolicy;
break;
}
}
return dndPolicy;
}
// Custom Edit Policy
public class BOMADragDropEditPolicy extends DragDropEditPolicy {
@Override
protected Command getDropElementCommand(EObject element,
DropObjectsRequest
request) {
EObject modelObj = getHostObject();
TransactionalEditingDomain editDomain =
(TransactionalEdit
ingDomain)WorkingCopyUtil.getWorkingCopyFor(modelObj).getEditingDomain();
return getGMFWrapper(new
BOMADragDropCommand(editDomain,request,modelObj,element));
}
private Command getGMFWrapper(ICommand gmfCommand){
return new ICommandProxy(gmfCommand);
}
//------
}
Step 6 : Execute the DnD Command to create the Concepts through corresponding
Generator class

4. public class BOMADragDropCommand extends AbstractTransactionalCommand{
private EObject modelObj;
private EObject element;
private IDataModelGenerator modelGen;
/**
*
* @param editDomain
* @param request
* @param modelObj
* @param element
*/
public BOMADragDropCommand (TransactionalEditingDomain
editDomain,DropObjectsRequest request,EObject modelObj,EObject element){
super(editDomain,"DND",getAffectedFiles(request));
this.modelObj = modelObj;
this.element = element;
}
@Override
protected CommandResult doExecuteWithResult(IProgressMonitor monitor,
IAdaptable info) throws ExecutionException {
Model model = null;
//
if(modelObj != null){
if(modelObj instanceof Model){
model = (Model)modelObj;
int elementType =
DropElementTypeResolver.getElementType(element);
switch(elementType){
case
DropElementTypeResolver.CONCEPT_TYPE:
modelGen = new
ConceptModelGenerator((Model)modelObj);
modelGen.generateUMLModel(element);
modelGen.setRelationships();
break;
case
DropElementTypeResolver.DB_TYPE:
modelGen = new
DB2UMLModelGenerator((Model)modelObj);
modelGen.generateUMLModel(element);
modelGen.setRelationships();
break;
case
DropElementTypeResolver.JAVA_TYPE:
break;
case
DropElementTypeResolver.XSD_TYPE:

5. break;
}
}
}
return CommandResult.newOKCommandResult();
}
private static List getAffectedFiles(Request request){
return null;
}
}