Decorating GEF figure using EditPolicy

In GMF there is a nifty DragDropEditPolicy that allows you to decorate EditPart's figure by changing background color thus indicating to the user that he is hovering over particular figure. I wanted to use this in my GEF editor, but unfortunately this policy does not exist in GEF.

To make use of this policy I made my plugin depend on import org.eclipse.gmf.runtime.diagram.ui.editpolicies and extended DragDropEditPolicy with my own

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1. public class DesignerDragDropEditPolicty extends DragDropEditPolicy {  
2.  private Label connectionLabel;  
3.  private PolylineConnection relationFigure;  
4.  private DesignerEditor editor;  
5.  private Image image;  
6.   
7.  public DesignerDragDropEditPolicty() {  
8.   connectionLabel = new Label();  
9.   connectionLabel.setOpaque(false);  
10.   image = DesignerUIPlugin.getDefault().getImageRegistry().get(ImageConstants.DROP_ICON);  
11.   connectionLabel.setIcon(image);  
12.     
13.  }  
14.    
15.  @Override  
16.  // remove icon when edit policy is done  
17.  public void eraseTargetFeedback(Request request) {  
18.   if(relationFigure != null){  
19.    if(relationFigure.getChildren().contains(connectionLabel)){  
20.     relationFigure.remove(connectionLabel);  
21.    }  
22.   }  
23.  }  
24.    
25.  // add icon on filtered edit part. Remove it when another edit part is hovered over.  
26.  public void showTargetFeedback(Request request) {  
27.   if(request instanceof CreateRequest){  
28.    editor = (DesignerEditor) DesignerUtil.getActiveDesignerTab();  
29.    Point location = ((CreateRequest)request).getLocation();  
30.    EditPart part = editor.getViewer().findObjectAt(location);  
31.   
32.    if(part instanceof RelationEditPart){  
33.     relationFigure = ((RelationEditPart)part).getConnection();  
34.     relationFigure.add(connectionLabel, new MidpointLocator(relationFigure, 0));  
35.     relationFigure.repaint();  
36.    }  
37.    else{  
38.     if(relationFigure != null){  
39.      if(relationFigure.getChildren().contains(connectionLabel)){  
40.       relationFigure.remove(connectionLabel);  
41.      }  
42.     }  
43.    }  
44.   }  
45.  }  
46. }  

public class DesignerDragDropEditPolicty extends DragDropEditPolicy {
 private Label connectionLabel;
 private PolylineConnection relationFigure;
 private DesignerEditor editor;
 private Image image;

 public DesignerDragDropEditPolicty() {
  connectionLabel = new Label();
  connectionLabel.setOpaque(false);
  image = DesignerUIPlugin.getDefault().getImageRegistry().get(ImageConstants.DROP_ICON);
  connectionLabel.setIcon(image);
  
 }
 
 @Override
 // remove icon when edit policy is done
 public void eraseTargetFeedback(Request request) {
  if(relationFigure != null){
   if(relationFigure.getChildren().contains(connectionLabel)){
    relationFigure.remove(connectionLabel);
   }
  }
 }
 
 // add icon on filtered edit part. Remove it when another edit part is hovered over.
 public void showTargetFeedback(Request request) {
  if(request instanceof CreateRequest){
   editor = (DesignerEditor) DesignerUtil.getActiveDesignerTab();
   Point location = ((CreateRequest)request).getLocation();
   EditPart part = editor.getViewer().findObjectAt(location);

   if(part instanceof RelationEditPart){
    relationFigure = ((RelationEditPart)part).getConnection();
    relationFigure.add(connectionLabel, new MidpointLocator(relationFigure, 0));
    relationFigure.repaint();
   }
   else{
    if(relationFigure != null){
     if(relationFigure.getChildren().contains(connectionLabel)){
      relationFigure.remove(connectionLabel);
     }
    }
   }
  }
 }
}

Instead of changing background of the figure as DragDropEditPolicy does I did something different. Whenever user passes inside an EditPart, in my case it's a relation, I put an icon signifying that in this case an object can be dropped onto existing connection an be created in the middle of the relation. I could have put a label saying "Drop here", but I think icons work better than words and after you get used to seeing a particular label with words it gets annoying.

Notice that in showTargetFeedback I filter out EditPart that I am interested in, so here code can be added to add different behavior for other parts.

Implementing “select on focus” behavior for an Eclipse Text control

http://stackoverflow.com/questions/10038570/implementing-select-on-focus-behavior-for-an-eclipse-text-control/10049615#10049615