ADT GLE2: Implement IViewRule.onChildSelected.

Revamp the IViewRule.on[Child]Selected to not return a closure.
There is no actual event at selection time.
Instead the callback is called directly to paint the canvas.

Change-Id: I2b50fbdff734b9c1a2c581ca5958bac43e5f325f

9 files changed, 232 insertions, 93 deletions

diff --git a/eclipse/plugins/com.android.ide.eclipse.adt/gscripts/android.view.View.groovy b/eclipse/plugins/com.android.ide.eclipse.adt/gscripts/android.view.View.groovy
index 2171cf3..ce491f5 100755
--- a/eclipse/plugins/com.android.ide.eclipse.adt/gscripts/android.view.View.groovy
+++ b/eclipse/plugins/com.android.ide.eclipse.adt/gscripts/android.view.View.groovy
@@ -17,16 +17,9 @@
 package com.android.adt.gscripts;
 
 import com.android.ide.eclipse.adt.editors.layout.gscripts.BaseViewRule;
+import com.android.ide.eclipse.adt.editors.layout.gscripts.IGraphics;
 import com.android.ide.eclipse.adt.editors.layout.gscripts.INode;
-import com.android.ide.eclipse.adt.editors.layout.gscripts.DropZone;
 import com.android.ide.eclipse.adt.editors.layout.gscripts.Rect;
-import com.android.ide.eclipse.adt.editors.layout.gscripts.Point;
-import com.android.ide.eclipse.adt.editors.layout.gscripts.IGraphics;
-
-import java.util.Map;
-import java.util.ArrayList;
-
-import groovy.lang.Closure;
 
 /**
  * An {@link IViewRule} for android.view.View and all its derived classes.
@@ -39,35 +32,49 @@ public class AndroidViewViewRule extends BaseViewRule {
     // fallback when navigating the hierarchy.
 
     // TODO move all this to BaseViewRule
-    Closure onSelected(INode node) {
-        def drawSelection = { gc, name, currentNode, isMultipleSelection ->
-            Rect r = currentNode.getBounds();
+    void onSelected(IGraphics gc, INode selectedNode,
+            String displayName, boolean isMultipleSelection) {
+        Rect r = selectedNode.getBounds();
 
-            if (!r.isValid()) {
-                return;
-            }
+        if (!r.isValid()) {
+            return;
+        }
 
-            gc.setLineWidth(1);
-            gc.setLineStyle(IGraphics.LineStyle.LINE_SOLID);
-            gc.drawRect(r);
+        gc.setLineWidth(1);
+        gc.setLineStyle(IGraphics.LineStyle.LINE_SOLID);
+        gc.drawRect(r);
 
-            if (name == null || isMultipleSelection) {
-                return;
-            }
+        if (displayName == null || isMultipleSelection) {
+            return;
+        }
 
-            int xs = r.x + 2;
-            int ys = r.y - gc.getFontHeight();
-            if (ys < 0) {
-                ys = r.y + r.h;
-            }
-            gc.drawString(name, xs, ys);
-        };
-
-        return drawSelection;
+        int xs = r.x + 2;
+        int ys = r.y - gc.getFontHeight();
+        if (ys < 0) {
+            ys = r.y + r.h;
+        }
+        gc.drawString(displayName, xs, ys);
     }
 
-    Closure onChildSelected(INode parentNode, INode childNode) {
-        return null;
+    void onChildSelected(IGraphics gc, INode parentNode, INode childNode) {
+        Rect rp = parentNode.getBounds();
+        Rect rc = childNode.getBounds();
+
+        if (rp.isValid() && rc.isValid()) {
+            gc.setLineWidth(1);
+            gc.setLineStyle(IGraphics.LineStyle.LINE_DOT);
+
+            // top line
+            int m = rc.x + rc.w / 2;
+            gc.drawLine(m, rc.y, m, rp.y);
+            // bottom line
+            gc.drawLine(m, rc.y + rc.h, m, rp.y + rp.h);
+            // left line
+            m = rc.y + rc.h / 2;
+            gc.drawLine(rc.x, m, rp.x, m);
+            // right line
+            gc.drawLine(rc.x + rc.w, m, rp.x + rp.w, m);
+        }
     }
 
 }
diff --git a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/INode.java b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/INode.java
index 8148850..da52b03 100755
--- a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/INode.java
+++ b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/INode.java
@@ -49,6 +49,18 @@ public interface INode {
      */
     Rect getBounds();
 
+
+    // ---- Hierarchy handling ----
+
+
+    /**
+     * Returns the parent node of this node, corresponding to the parent view in the layout.
+     * The returned parent can be null when the node is the root element, or when the node is
+     * not yet or no longer attached to the hierarchy.
+     */
+    INode getParent();
+
+
     // ---- XML Editing ---
 
     /**
diff --git a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/IViewRule.java b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/IViewRule.java
index 33ea938..e287885 100755
--- a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/IViewRule.java
+++ b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/IViewRule.java
@@ -16,8 +16,6 @@
 
 package com.android.ide.eclipse.adt.editors.layout.gscripts;
 
-import groovy.lang.Closure;
-
 import java.util.ArrayList;
 import java.util.Map;
 
@@ -73,22 +71,32 @@ public interface IViewRule {
 
     /**
      * Called by the canvas when a view is being selected.
-     * The callback must return a closure that is used to draw the actual selection.
-     * <p/>
-     * The closure takes 4 arguments: <br/>
-     * - An {@link IGraphics} instance, to perform drawing operations.  <br/>
-     * - The name to display, as returned by {@link #getDisplayName()}. <br/>
-     * - The selected {@link INode}. <br/>
-     * - A boolean set to true if more than one element is selected.
      * <p/>
-     * Context: foreground color already set to selection color, full opaque.
+     * Before the method is called, the canvas' Graphic Context is initialized
+     * with a foreground color already set to the desired selection color, fully
+     * opaque and with the default adequate font.
      *
+     * @param gc An {@link IGraphics} instance, to perform drawing operations.
      * @param selectedNode The node selected. Never null.
-     * @return Null or a closure that expects graphics, name, currentNode as input arguments.
+     * @param displayName The name to display, as returned by {@link #getDisplayName()}.
+     * @param isMultipleSelection A boolean set to true if more than one element is selected.
      */
-    Closure onSelected(INode selectedNode);
+    void onSelected(IGraphics gc, INode selectedNode,
+            String displayName, boolean isMultipleSelection);
 
-    Closure onChildSelected(INode parentNode, INode childNode);
+    /**
+     * Called by the canvas when a single child view is being selected.
+     * <p/>
+     * Note that this is called only for single selections.
+     * <p/>
+     * This allows a parent to draw stuff around its children, for example to display
+     * layout attributes graphically.
+     *
+     * @param gc An {@link IGraphics} instance, to perform drawing operations.
+     * @param parentNode The parent of the node selected. Never null.
+     * @param childNode The child node that was selected. Never null.
+     */
+    void onChildSelected(IGraphics gc, INode parentNode, INode childNode);
 
     // ==== XML Creation ====
 
diff --git a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/Rect.java b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/Rect.java
index 3f0754d..ad8e45b 100755
--- a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/Rect.java
+++ b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/editors/layout/gscripts/Rect.java
@@ -40,6 +40,16 @@ public class Rect {
     }
 
     /** Initialize rectangle to the given values. They can be invalid. */
+    public Rect(Rect r) {
+        set(r);
+    }
+
+    /** Initialize rectangle to the given values. They can be invalid. */
+    public Rect(Rectangle swtRect) {
+        set(swtRect);
+    }
+
+    /** Initialize rectangle to the given values. They can be invalid. */
     public void set(int x, int y, int w, int h) {
         this.x = x;
         this.y = y;
@@ -49,10 +59,12 @@ public class Rect {
 
     /** Initialize rectangle to match the given one. */
     public void set(Rect r) {
-        x = r.x;
-        y = r.y;
-        w = r.w;
-        h = r.h;
+        set(r.x, r.y, r.w, r.h);
+    }
+
+    /** Initialize rectangle to match the given one. */
+    public void set(Rectangle swtRect) {
+        set(swtRect.x, swtRect.y, swtRect.width, swtRect.height);
     }
 
     /** Returns a new instance of a rectangle with the same values. */
diff --git a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gle2/CanvasSelection.java b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gle2/CanvasSelection.java
index 2ba8e3f..29d14b5 100755
--- a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gle2/CanvasSelection.java
+++ b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gle2/CanvasSelection.java
@@ -16,33 +16,30 @@
 
 package com.android.ide.eclipse.adt.internal.editors.layout.gle2;
 
-import com.android.ide.eclipse.adt.editors.layout.gscripts.IViewRule;
+import com.android.ide.eclipse.adt.editors.layout.gscripts.INode;
 import com.android.ide.eclipse.adt.internal.editors.layout.gre.NodeFactory;
 import com.android.ide.eclipse.adt.internal.editors.layout.gre.NodeProxy;
 import com.android.ide.eclipse.adt.internal.editors.layout.gre.RulesEngine;
 
 import org.eclipse.swt.graphics.Rectangle;
 
-import groovy.lang.Closure;
-
 /**
  * Represents one selection in {@link LayoutCanvas}.
  */
 /* package */ class CanvasSelection {
 
-    /** Current selected view info. Cannot be null. */
+    /** Current selected view info. Can be null. */
     private final CanvasViewInfo mCanvasViewInfo;
 
-    /** Current selection border rectangle. Cannot be null. */
+    /** Current selection border rectangle. Null when mCanvasViewInfo is null . */
     private final Rectangle mRect;
 
+    /** The node proxy for drawing the selection. Null when mCanvasViewInfo is null. */
+    private final NodeProxy mNodeProxy;
+
     /** The name displayed over the selection, typically the widget class name. Can be null. */
     private final String mName;
 
-    /** Closure to use to paint the selection. */
-    private Closure mPaintClosure;
-
-    private NodeProxy mNodeProxy;
 
     /**
      * Creates a new {@link CanvasSelection} object.
@@ -59,6 +56,7 @@ import groovy.lang.Closure;
 
         if (canvasViewInfo == null) {
             mRect = null;
+            mNodeProxy = null;
         } else {
             Rectangle r = canvasViewInfo.getSelectionRect();
             mRect = new Rectangle(
@@ -66,11 +64,10 @@ import groovy.lang.Closure;
                     r.y + LayoutCanvas.IMAGE_MARGIN,
                     r.width,
                     r.height);
+            mNodeProxy = nodeFactory.create(canvasViewInfo);
         }
 
         mName = initDisplayName(canvasViewInfo, gre);
-
-        initSelectedDisplay(canvasViewInfo, nodeFactory, gre);
     }
 
     /**
@@ -97,19 +94,29 @@ import groovy.lang.Closure;
     }
 
     /**
-     * Calls the closure returned by
-     * {@link IViewRule#onSelected(com.android.ide.eclipse.adt.editors.layout.gscripts.INode)}.
+     * Calls IViewRule.onSelected on the selected view.
      *
+     * @param gre The rules engines.
      * @param gcWrapper The GC to use for drawing.
      * @param isMultipleSelection True if more than one view is selected.
      */
-    /*package*/ void paint(GCWrapper gcWrapper, boolean isMultipleSelection) {
-        if (mPaintClosure != null) {
-            try {
-                mPaintClosure.call(
-                        new Object[] { gcWrapper, mName, mNodeProxy, isMultipleSelection });
-            } catch (Exception e) {
-                mNodeProxy.debugPrintf("Selection Paint Closure: %s", e.toString());
+    /*package*/ void paintSelection(RulesEngine gre, GCWrapper gcWrapper, boolean isMultipleSelection) {
+        if (mNodeProxy != null) {
+            gre.callOnSelected(gcWrapper, mNodeProxy, mName, isMultipleSelection);
+        }
+    }
+
+    /**
+     * Calls IViewRule.onChildSelected on the parent of the selected view, if it has one.
+     *
+     * @param gre The rules engines.
+     * @param gcWrapper The GC to use for drawing.
+     */
+    public void paintParentSelection(RulesEngine gre, GCWrapper gcWrapper) {
+        if (mNodeProxy != null) {
+            INode parent = mNodeProxy.getParent();
+            if (parent instanceof NodeProxy) {
+                gre.callOnChildSelected(gcWrapper, (NodeProxy)parent, mNodeProxy);
             }
         }
     }
@@ -152,14 +159,4 @@ import groovy.lang.Closure;
 
         return name;
     }
-
-    private void initSelectedDisplay(CanvasViewInfo canvasViewInfo,
-            NodeFactory nodeFactory,
-            RulesEngine gre) {
-        NodeProxy proxy = nodeFactory.create(canvasViewInfo);
-        Closure result = gre.callOnSelected(proxy);
-
-        mNodeProxy = proxy;
-        mPaintClosure = result;
-    }
 }
diff --git a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gle2/LayoutCanvas.java b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gle2/LayoutCanvas.java
index 8bb38eb..21de9c5 100755
--- a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gle2/LayoutCanvas.java
+++ b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gle2/LayoutCanvas.java
@@ -274,6 +274,8 @@ import java.util.ListIterator;
             mLastValidViewInfoRoot = new CanvasViewInfo(result.getRootView());
             setImage(result.getImage());
 
+            updateNodeProxies(mLastValidViewInfoRoot);
+
             // Check if the selection is still the same (based on the object keys)
             // and eventually recompute their bounds.
             for (ListIterator<CanvasSelection> it = mSelections.listIterator(); it.hasNext(); ) {
@@ -357,6 +359,33 @@ import java.util.ListIterator;
 
     //---
 
+
+    /**
+     * Creates or updates the node proxy for this canvas view info.
+     * <p/>
+     * Since proxies are reused, this will update the bounds of an existing proxy when the
+     * canvas is refreshed and a view changes position or size.
+     * <p/>
+     * This is a recursive call that updates the whole hierarchy starting at the given
+     * view info.
+     */
+    private void updateNodeProxies(CanvasViewInfo vi) {
+
+        if (vi == null) {
+            return;
+        }
+
+        UiViewElementNode key = vi.getUiViewKey();
+
+        if (key != null) {
+            mNodeFactory.create(vi);
+        }
+
+        for (CanvasViewInfo child : vi.getChildren()) {
+            updateNodeProxies(child);
+        }
+    }
+
     /**
      * Sets the image of the last *successful* rendering.
      * Converts the AWT image into an SWT image.
@@ -429,12 +458,22 @@ import java.util.ListIterator;
                 gc.drawRectangle(mHoverRect);
             }
 
-            gc.setForeground(mSelectionFgColor);
-            boolean isMultipleSelection = mSelections.size() > 1;
-            for (CanvasSelection s : mSelections) {
-                s.paint(mGCWrapper, isMultipleSelection);
+            int n = mSelections.size();
+            if (n > 0) {
+                boolean isMultipleSelection = n > 1;
+
+                if (n == 1) {
+                    gc.setForeground(mSelectionFgColor);
+                    mSelections.get(0).paintParentSelection(mRulesEngine, mGCWrapper);
+                }
+
+                for (CanvasSelection s : mSelections) {
+                    gc.setForeground(mSelectionFgColor);
+                    s.paintSelection(mRulesEngine, mGCWrapper, isMultipleSelection);
+                }
             }
 
+
             drawDropZones(gc);
 
         } finally {
diff --git a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/NodeFactory.java b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/NodeFactory.java
index 2b56c3a..d6251c8 100755
--- a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/NodeFactory.java
+++ b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/NodeFactory.java
@@ -61,9 +61,14 @@ public class NodeFactory {
     private NodeProxy create(UiViewElementNode uiNode, Rectangle bounds) {
         NodeProxy proxy = mNodeMap.get(uiNode);
 
-        if (proxy == null || !proxy.getBounds().equals(bounds)) {
+        if (proxy == null) {
+            // Create a new proxy if the key doesn't exist
             proxy = new NodeProxy(uiNode, bounds, this);
             mNodeMap.put(uiNode, proxy);
+
+        } else if (bounds != null && !proxy.getBounds().equals(bounds)) {
+            // Update the bounds if necessary
+            proxy.setBounds(bounds);
         }
 
         return proxy;
diff --git a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/NodeProxy.java b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/NodeProxy.java
index d0c1568..02d2d57 100755
--- a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/NodeProxy.java
+++ b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/NodeProxy.java
@@ -55,19 +55,23 @@ public class NodeProxy implements INode {
      * Creates a new {@link INode} that wraps an {@link UiViewElementNode} that is
      * actually valid in the current UI/XML model. The view may not be part of the canvas
      * yet (e.g. if it has just been dynamically added and the canvas hasn't reloaded yet.)
+     * <p/>
+     * This method is package protected. To create a node, please use {@link NodeFactory} instead.
      *
      * @param uiNode The node to wrap.
-     * @param bounds The bounds of a the view in the canvas. Must be a valid rect for a view
-     *   that is actually in the canvas and must be null (or an invalid rect) for a view
-     *   that has just been added dynamically to the model.
+     * @param bounds The bounds of a the view in the canvas. Must be either: <br/>
+     *   - a valid rect for a view that is actually in the canvas <br/>
+     *   - <b>*or*</b> null (or an invalid rect) for a view that has just been added dynamically
+     *   to the model. We never store a null bounds rectangle in the node, a null rectangle
+     *   will be converted to an invalid rectangle.
      */
-    public NodeProxy(UiViewElementNode uiNode, Rectangle bounds, NodeFactory factory) {
+    /*package*/ NodeProxy(UiViewElementNode uiNode, Rectangle bounds, NodeFactory factory) {
         mNode = uiNode;
         mFactory = factory;
         if (bounds == null) {
             mBounds = new Rect();
         } else {
-            mBounds = new Rect(bounds.x, bounds.y, bounds.width, bounds.height);
+            mBounds = new Rect(bounds);
         }
     }
 
@@ -82,10 +86,34 @@ public class NodeProxy implements INode {
         return mBounds;
     }
 
+
+    /**
+     * Updates the bounds of this node proxy. Bounds cannot be null, but it can be invalid.
+     * This is a package-protected method, only the {@link NodeFactory} uses this method.
+     */
+    /*package*/ void setBounds(Rectangle bounds) {
+        mBounds.set(bounds);
+    }
+
     /* package */ UiViewElementNode getNode() {
         return mNode;
     }
 
+
+    // ---- Hierarchy handling ----
+
+    public INode getParent() {
+        if (mNode != null) {
+            UiElementNode p = mNode.getUiParent();
+            if (p instanceof UiViewElementNode) {
+                return mFactory.create((UiViewElementNode) p);
+            }
+        }
+
+        return null;
+    }
+
+
     // ---- XML Editing ---
 
     public void editXml(String undoName, final Closure c) {
diff --git a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/RulesEngine.java b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/RulesEngine.java
index 94588b2..12c2dd7 100755
--- a/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/RulesEngine.java
+++ b/eclipse/plugins/com.android.ide.eclipse.adt/src/com/android/ide/eclipse/adt/internal/editors/layout/gre/RulesEngine.java
@@ -19,6 +19,7 @@ package com.android.ide.eclipse.adt.internal.editors.layout.gre;
 import com.android.ide.eclipse.adt.AdtPlugin;
 import com.android.ide.eclipse.adt.AndroidConstants;
 import com.android.ide.eclipse.adt.editors.layout.gscripts.DropZone;
+import com.android.ide.eclipse.adt.editors.layout.gscripts.IGraphics;
 import com.android.ide.eclipse.adt.editors.layout.gscripts.INode;
 import com.android.ide.eclipse.adt.editors.layout.gscripts.IViewRule;
 import com.android.ide.eclipse.adt.editors.layout.gscripts.Point;
@@ -35,7 +36,6 @@ import org.eclipse.core.resources.IProject;
 import org.eclipse.core.resources.IResource;
 import org.eclipse.core.resources.IResourceDelta;
 
-import groovy.lang.Closure;
 import groovy.lang.GroovyClassLoader;
 
 import java.io.InputStream;
@@ -113,23 +113,54 @@ public class RulesEngine {
         return null;
     }
 
-    public Closure callOnSelected(NodeProxy selectedNode) {
+    /**
+     * Invokes {@link IViewRule#onSelected(IGraphics, INode, String, boolean)}
+     * on the rule matching the specified element.
+     *
+     * @param gc An {@link IGraphics} instance, to perform drawing operations.
+     * @param selectedNode The node selected. Never null.
+     * @param displayName The name to display, as returned by {@link IViewRule#getDisplayName()}.
+     * @param isMultipleSelection A boolean set to true if more than one element is selected.
+     */
+    public void callOnSelected(IGraphics gc, NodeProxy selectedNode,
+            String displayName, boolean isMultipleSelection) {
         // try to find a rule for this element's FQCN
         IViewRule rule = loadRule(selectedNode.getNode());
 
         if (rule != null) {
             try {
-                return rule.onSelected(selectedNode);
+                rule.onSelected(gc, selectedNode, displayName, isMultipleSelection);
 
             } catch (Exception e) {
-                logError("%s.getDisplayName() failed: %s",
+                logError("%s.onSelected() failed: %s",
                         rule.getClass().getSimpleName(),
                         e.toString());
             }
         }
+    }
 
-        return null;
+    /**
+     * Invokes {@link IViewRule#onChildSelected(IGraphics, INode, INode)}
+     * on the rule matching the specified element.
+     *
+     * @param gc An {@link IGraphics} instance, to perform drawing operations.
+     * @param parentNode The parent of the node selected. Never null.
+     * @param childNode The child node that was selected. Never null.
+     */
+    public void callOnChildSelected(IGraphics gc, NodeProxy parentNode, NodeProxy childNode) {
+        // try to find a rule for this element's FQCN
+        IViewRule rule = loadRule(parentNode.getNode());
 
+        if (rule != null) {
+            try {
+                rule.onChildSelected(gc, parentNode, childNode);
+
+            } catch (Exception e) {
+                logError("%s.onChildSelected() failed: %s",
+                        rule.getClass().getSimpleName(),
+                        e.toString());
+            }
+        }
     }
 
     /**