added support for dragover effects,

fixed NPE


git-svn-id: https://samskivert.googlecode.com/svn/trunk@817 6335cc39-0255-0410-8fd6-9bcaacd3b74c

projects/samskivert/src/java/com/samskivert/swing/dnd/DnDManager.java

@@ -1,5 +1,5 @@
 //
-// $Id: DnDManager.java,v 1.2 2002/08/20 21:05:10 ray Exp $
+// $Id: DnDManager.java,v 1.3 2002/08/20 22:38:42 ray Exp $
 
 package com.samskivert.swing.dnd;
 
@@ -104,7 +104,7 @@ public class DnDManager
         _source = (DragSource) _draggers.get(_sourceComp);
 
         // make sure the source wants to start a drag.
-        if (!_source.startDrag(_cursors, _data)) {
+        if ((_source == null) || (!_source.startDrag(_cursors, _data))) {
             // if not, reset our start conditions and bail
             reset();
             return;
@@ -166,10 +166,13 @@ public class DnDManager
      */
     protected void mouseExited (MouseEvent event)
     {
-        _lastTarget = null;
         if (_lastComp != null) {
             _lastComp.setCursor(_oldCursor);
         }
+        if (_lastTarget != null) {
+            _lastTarget.noDrop();
+            _lastTarget = null;
+        }
     }
 
     /**

projects/samskivert/src/java/com/samskivert/swing/dnd/DropTarget.java

@@ -1,5 +1,5 @@
 //
-// $Id: DropTarget.java,v 1.1 2002/08/20 02:49:19 ray Exp $
+// $Id: DropTarget.java,v 1.2 2002/08/20 22:38:42 ray Exp $
 
 package com.samskivert.swing.dnd;
 
@@ -11,9 +11,20 @@ public interface DropTarget
 {
     /**
      * Return true if the specified drop should be allowed on this target.
+     * Also indicates that a hover has started in case the drop target would
+     * like to create dragover feedback aside from the cursor feedback.
+     *
+     * If this method returns true then either dropCompleted or hoverEnd
+     * will be called next.
      */
     public boolean checkDrop (DragSource source, Object peekdata);
 
+    /**
+     * Called to let the DropTarget know that we've stopped hovering over
+     * but did not actually drop.
+     */
+    public void noDrop ();
+
     /**
      * Called when the drop is actually executed.
      */