diff -r 43db124d472c openide.explorer/apichanges.xml
--- a/openide.explorer/apichanges.xml	Mon Dec 14 17:14:42 2009 +0100
+++ b/openide.explorer/apichanges.xml	Mon Dec 14 17:58:10 2009 +0100
@@ -47,6 +47,17 @@
 <apidef name="explorer">Explorer API</apidef>
 </apidefs>
 <changes>
+    <change id="OutlineView.setTreeSortable">
+        <api name="explorer"/>
+        <summary><code>OutlineView.setTreeSortable</code> added.</summary>
+        <version major="6" minor="24"/>
+        <date day="21" month="12" year="2009"/>
+        <author login="mentlicher"/>
+        <compatibility binary="compatible" source="compatible" deprecation="no" deletion="no" addition="yes"/>
+        <description>Added method to set or unset the tree column as sortable.</description>
+        <class package="org.openide.explorer.view" name="OutlineView"/>
+        <issue number="178613"/>
+    </change>
     <change id="TreeView.setAutoWaitCursor">
         <api name="explorer"/>
         <summary><code>TreeView.setAutoWaitCursor</code> added.</summary>
diff -r 43db124d472c openide.explorer/nbproject/project.properties
--- a/openide.explorer/nbproject/project.properties	Mon Dec 14 17:14:42 2009 +0100
+++ b/openide.explorer/nbproject/project.properties	Mon Dec 14 17:58:10 2009 +0100
@@ -44,4 +44,4 @@
 javadoc.arch=${basedir}/arch.xml
 javadoc.apichanges=${basedir}/apichanges.xml
 
-spec.version.base=6.23.0
+spec.version.base=6.24.0
diff -r 43db124d472c openide.explorer/src/org/openide/explorer/view/OutlineView.java
--- a/openide.explorer/src/org/openide/explorer/view/OutlineView.java	Mon Dec 14 17:14:42 2009 +0100
+++ b/openide.explorer/src/org/openide/explorer/view/OutlineView.java	Mon Dec 14 17:58:10 2009 +0100
@@ -118,7 +118,7 @@
 public class OutlineView extends JScrollPane {
 
     /** The table */
-    private Outline outline;
+    private OutlineViewOutline outline;
     /** Explorer manager, valid when this view is showing */
     ExplorerManager manager;
     /** not null if popup menu enabled */
@@ -284,6 +284,16 @@
             popupListener = null;
             return;
         }
+    }
+
+    /**
+     * Set the tree column as sortable
+     * @param treeSortable <code>true</code> to make the tree column sortable,
+     *        <code>false</code> otherwise. The tree column is sortable by default.
+     * @since 6.24
+     */
+    public void setTreeSortable(boolean treeSortable) {
+        outline.setTreeSortable(treeSortable);
     }
     
     /** Initializes the component and lookup explorer manager.
@@ -882,6 +892,9 @@
     private static class OutlineViewOutline extends Outline {
         private final PropertiesRowModel rowModel;
         private static final String COLUMNS_SELECTOR_HINT = "ColumnsSelectorHint"; // NOI18N
+
+        private boolean treeSortable = true;
+
         public OutlineViewOutline(OutlineModel mdl, PropertiesRowModel rowModel) {
             super(mdl);
             this.rowModel = rowModel;
@@ -993,6 +1006,14 @@
             return new OutlineViewOutlineColumn(modelIndex);
         }
 
+        boolean isTreeSortable() {
+            return this.treeSortable;
+        }
+
+        void setTreeSortable(boolean treeSortable) {
+            this.treeSortable = treeSortable;
+        }
+
         /**
          * Extension of ETableColumn using TableViewRowComparator as
          * comparator.
@@ -1006,20 +1027,17 @@
             }
             @Override
             public boolean isSortingAllowed() {
-                boolean res = super.isSortingAllowed();
-                TableModel model = getModel();
-                if (model.getRowCount() <= 0) {
-                    return res;
+                int index = getModelIndex();
+                Object sortable;
+                if (index > 0) {
+                    sortable = rowModel.getPropertyValue("SortableColumn", index - 1); // NOI18N
+                } else {
+                    return isTreeSortable();
                 }
-                Object sampleValue = model.getValueAt(0, getModelIndex());
-                if (sampleValue instanceof Node.Property) {
-                    Node.Property prop = (Node.Property)sampleValue;
-                    Object sortableColumnProperty = prop.getValue("SortableColumn");
-                    if (sortableColumnProperty instanceof Boolean) {
-                        return ((Boolean)sortableColumnProperty).booleanValue();
-                    }
+                if (sortable != null) {
+                    return Boolean.TRUE.equals(sortable);
                 }
-                return res;
+                return super.isSortingAllowed();
             }
 
             @Override
diff -r 43db124d472c openide.explorer/src/org/openide/explorer/view/PropertiesRowModel.java
--- a/openide.explorer/src/org/openide/explorer/view/PropertiesRowModel.java	Mon Dec 14 17:14:42 2009 +0100
+++ b/openide.explorer/src/org/openide/explorer/view/PropertiesRowModel.java	Mon Dec 14 17:58:10 2009 +0100
@@ -333,6 +333,10 @@
         return -1;
     }
 
+    Object getPropertyValue(String propName, int column) {
+        return prop[column].getValue(propName);
+    }
+
     /**
      * Changes the value of the boolean property.
      */