Show no context menu instead of throwing for objects without one

CADability/MenuResource.cs

@@ -304,14 +304,16 @@ static public MenuWithHandler[] CreateContextMenuWithHandler(string[] menuIDs, I
         /// <param name="MenuName">Name of the menu to load: the "Name" attribute of a "MainMenu" node or the "MenuId" attribute of a "Popup" node</param>
         /// <param name="main">true to load a main menu, false to load a popup (context) menu</param>
         /// <param name="handler">Command handler which handles the menu commands</param>
-        /// <returns>The menu entries</returns>
+        /// <returns>The menu entries, an empty array if there is no menu with this name (e.g. for a null name)</returns>
         static public MenuWithHandler[] LoadMenuDefinition(string MenuName, bool main, ICommandHandler handler)
         {
             List<MenuWithHandler> result = new List<MenuWithHandler>();
             ICommandHandler Handler = handler;
+            if (MenuName == null) return result.ToArray(); // e.g. an object without a context menu of its own, like a picture
             XmlNode MenuNode;
             if (main) MenuNode = mMenuDocument.SelectSingleNode("Menus/MainMenu[@Name='" + MenuName + "']");
             else MenuNode = mMenuDocument.SelectSingleNode("Menus//Popup[@MenuId='" + MenuName + "']");
+            if (MenuNode == null) return result.ToArray();
             for (XmlNode nd = MenuNode.FirstChild; nd != null; nd = nd.NextSibling)
             {
                 LoadMenu(nd, result, Handler);

CADability/UnscaledGeoObject.cs

@@ -343,7 +343,7 @@ IGeoObject IGeoObjectShowProperty.GetGeoObject()
 
         string IGeoObjectShowProperty.GetContextMenuId()
         {
-            throw new Exception("The method or operation is not implemented.");
+            return null; // no context menu of its own
         }
 
         #endregion

CADability/UnscaledIcon.cs

@@ -338,7 +338,7 @@ IGeoObject IGeoObjectShowProperty.GetGeoObject()
 
         string IGeoObjectShowProperty.GetContextMenuId()
         {
-            throw new Exception("The method or operation is not implemented.");
+            return null; // no context menu of its own
         }
 
         #endregion

tests/CADability.Tests/ContextMenuTests.cs

@@ -0,0 +1,45 @@
+using CADability.GeoObject;
+using CADability.UserInterface;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace CADability.Tests
+{
+    /// <summary>
+    /// The context menu of a selected object: <see cref="CADability.Actions.SelectObjectsAction"/> loads the menu whose id the object's
+    /// <see cref="IGeoObjectShowProperty"/> returns. Pictures, icons and unscaled objects have no menu of their own and
+    /// return null; a right click on a selected picture threw a NullReferenceException in
+    /// <see cref="MenuResource.LoadMenuDefinition"/>.
+    /// </summary>
+    [TestClass]
+    public class ContextMenuTests
+    {
+        [TestMethod]
+        public void AMissingMenuIsEmpty()
+        {
+            Assert.AreEqual(0, MenuResource.LoadMenuDefinition(null, false, null).Length);
+            Assert.AreEqual(0, MenuResource.LoadMenuDefinition("MenuId.DoesNotExist", false, null).Length);
+            Assert.AreEqual(0, MenuResource.LoadMenuDefinition("No Such Main Menu", true, null).Length);
+        }
+
+        [TestMethod]
+        public void AnExistingMenuIsLoaded()
+        {
+            // the context menu of the path of a picture
+            MenuWithHandler[] menu = MenuResource.LoadMenuDefinition("MenuId.Picture.Path", false, null);
+            CollectionAssert.AreEqual(new[] { "MenuId.Picture.Path.Reload", "MenuId.Picture.Path.Open" }, menu.Select(m => m.ID).ToArray());
+        }
+
+        [TestMethod]
+        [DataRow(typeof(ShowPropertyPicture))]
+        [DataRow(typeof(ShowPropertyUnscaledIcon))]
+        [DataRow(typeof(ShowPropertyUnscaledGeoObject))]
+        public void TheContextMenuOfObjectsWithoutAMenuOfTheirOwnCanBeLoaded(Type showPropertyType)
+        {
+            // what SelectObjectsAction.OnMouseUp does for a single selected object; the id does not depend on the state
+            // of the property, so an uninitialized one (without a frame) is enough
+            IGeoObjectShowProperty showProperty = (IGeoObjectShowProperty)System.Runtime.CompilerServices.RuntimeHelpers.GetUninitializedObject(showPropertyType);
+            MenuWithHandler[] menu = MenuResource.LoadMenuDefinition(showProperty.GetContextMenuId(), false, showProperty as ICommandHandler);
+            Assert.AreEqual(0, menu.Length);
+        }
+    }
+}