How to add DropListener to drop text in a draw2d Label

Question

I am Trying to add a dropListener so I can Drop and text into a draw2d Label ,in GEf Editor , Can anyone help how Can I do that. An example will be great.

Answer 1

To respond to drop events on a GEF edit part viewer you have to install on the viewer itself an implementation of org.eclipse.jface.util.TransferDropTargetListener that understands transfers of type org.eclipse.swt.dnd.TextTransfer and that creates some kind of org.eclipse.gef.Request that can be handled by an org.eclipse.gef.EditPolicy installed on the target org.eclipse.gef.EditPart.

You have to understand that both the Request and the EditPolicy allow you to customize the drop behavior on a EditPart basis. As a consequence, I can show you an example that is actually fully functional, but feel free to customize it to your real needs.

First create the TransferDropTargetListener:

public class TextTransferDropTargetListener extends AbstractTransferDropTargetListener {

    public TextTransferDropTargetListener(EditPartViewer viewer) {
        super(viewer, TextTransfer.getInstance());
    }

    @Override
    protected void handleDragOver() {
        getCurrentEvent().feedback = DND.FEEDBACK_SCROLL | DND.FEEDBACK_EXPAND;
        super.handleDragOver();
    }

    @Override
    protected Request createTargetRequest() {
        return new ChangeBoundsRequest(REQ_ADD);
    }

    @Override
    protected void updateTargetRequest() {
        ChangeBoundsRequest request = (ChangeBoundsRequest) getTargetRequest();
        request.setEditParts(Collections.EMPTY_LIST);
        request.setLocation(getDropLocation());
    }

    @Override
    protected void handleDrop() {
        super.handleDrop();
        if (getCurrentEvent().detail != DND.DROP_NONE) {
            getViewer().setSelection(StructuredSelection.EMPTY);
            getViewer().getControl().setFocus();
        }
    }

    @Override
    protected Command getCommand() {
        String text = (String) getCurrentEvent().data; 
        List<IEntityPart> editParts = new ArrayList<IEntityPart>();

        //
        // using the 'text' variable you have to create
        // a new EditPart that would eventually replace the old one.
        //
        editParts.add(createNewLabelPart());

        ChangeBoundsRequest request = (ChangeBoundsRequest) getTargetRequest();
        request.setEditParts(editParts);

        return super.getCommand();
    }
}

then install the listener in the graphical viewer constructor using the following statement:

addDropTargetListener(new TextTransferDropTargetListener(this));

finally ensure that an EditPolicy that understands requests of type REQ_ADD (maybe you already added one that extends LayoutEditPolicy or ContainerEditPolicy) is installed on the target EditPart, which is usually done in the AbstractEditPart.createEditPolicies().

To better understand the chain of responsibilities, I suggest you to have a look at the super implementation of the TransferDropTargetListener.getCommand() method.