Adding support for RazorView.IsSectionDefined

src/Microsoft.AspNet.Mvc.Razor/Properties/Resources.Designer.cs

@@ -170,6 +170,22 @@ namespace Microsoft.AspNet.Mvc.Razor
             return string.Format(CultureInfo.CurrentCulture, GetString("ViewEngine_ViewNotFound"), p0, p1);
         }
 
+        /// <summary>
+        /// The method '{0}' cannot be invoked by this view.
+        /// </summary>
+        internal static string View_MethodCannotBeCalled
+        {
+            get { return GetString("View_MethodCannotBeCalled"); }
+        }
+
+        /// <summary>
+        /// The method '{0}' cannot be invoked by this view.
+        /// </summary>
+        internal static string FormatView_MethodCannotBeCalled(object p0)
+        {
+            return string.Format(CultureInfo.CurrentCulture, GetString("View_MethodCannotBeCalled"), p0);
+        }
+
         private static string GetString(string name, params string[] formatterNames)
         {
             var value = _resourceManager.GetString(name);

src/Microsoft.AspNet.Mvc.Razor/RazorView.cs

@@ -259,6 +259,12 @@ namespace Microsoft.AspNet.Mvc.Razor
             SectionWriters[name] = action;
         }
 
+        public bool IsSectionDefined([NotNull] string name)
+        {
+            EnsureMethodCanBeInvoked("IsSectionDefined");
+            return PreviousSectionWriters.ContainsKey(name);
+        }
+
         public HelperResult RenderSection([NotNull] string name)
         {
             return RenderSection(name, required: true);
@@ -266,9 +272,10 @@ namespace Microsoft.AspNet.Mvc.Razor
 
         public HelperResult RenderSection([NotNull] string name, bool required)
         {
+            EnsureMethodCanBeInvoked("RenderSection");
+
             HelperResult action;
-            if (PreviousSectionWriters != null &&
-                PreviousSectionWriters.TryGetValue(name, out action))
+            if (PreviousSectionWriters.TryGetValue(name, out action))
             {
                 return action;
             }
@@ -283,5 +290,13 @@ namespace Microsoft.AspNet.Mvc.Razor
                 return null;
             }
         }
+
+        private void EnsureMethodCanBeInvoked(string methodName)
+        {
+            if (PreviousSectionWriters == null)
+            {
+                throw new InvalidOperationException(Resources.FormatView_MethodCannotBeCalled(methodName));
+            }
+        }
     }
 }

src/Microsoft.AspNet.Mvc.Razor/Resources.resx

@@ -147,4 +147,7 @@
   <data name="ViewEngine_ViewNotFound" xml:space="preserve">
     <value>The view '{0}' was not found. The following locations were searched:{1}.</value>
   </data>
+  <data name="View_MethodCannotBeCalled" xml:space="preserve">
+    <value>The method '{0}' cannot be invoked by this view.</value>
+  </data>
 </root>

test/Microsoft.AspNet.Mvc.Razor.Test/RazorViewTest.cs

@@ -2,6 +2,7 @@
 using System.IO;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc.Rendering;
+using Microsoft.AspNet.Testing;
 using Moq;
 using Xunit;
 
@@ -56,6 +57,25 @@ namespace Microsoft.AspNet.Mvc.Razor.Test
             Assert.Same(actual, expected);
         }
 
+        [Fact]
+        public async Task RenderSection_ThrowsIfNoPreviousPage()
+        {
+            // Arrange
+            Exception ex = null;
+            var view = CreateView(v =>
+            {
+                ex = Assert.Throws<InvalidOperationException>(() => v.RenderSection("bar"));
+            });
+            var viewContext = CreateViewContext(layoutView: null);
+
+            // Act
+            await view.RenderAsync(viewContext);
+
+            // Assert
+            Assert.Equal("The method 'RenderSection' cannot be invoked by this view.",
+                         ex.Message);
+        }
+
         [Fact]
         public async Task RenderSection_ThrowsIfRequiredSectionIsNotFound()
         {
@@ -80,7 +100,63 @@ namespace Microsoft.AspNet.Mvc.Razor.Test
             // Assert
             Assert.Equal("Section 'bar' is not defined.", ex.Message);
         }
-        
+
+        [Fact]
+        public void IsSectionDefined_ThrowsIfNoPreviousExecutingPage()
+        {
+            // Arrange
+            var view = CreateView(v => { });
+            var viewContext = CreateViewContext(layoutView: null);
+
+            // Act and Assert
+            ExceptionAssert.Throws<InvalidOperationException>(() => view.IsSectionDefined("foo"),
+                "The method 'IsSectionDefined' cannot be invoked by this view.");
+        }
+
+        [Fact]
+        public async Task IsSectionDefined_ReturnsFalseIfSectionNotDefined()
+        {
+            // Arrange
+            bool? actual = null;
+            var view = CreateView(v =>
+            {
+                v.DefineSection("baz", new HelperResult(writer => { }));
+                v.Layout = LayoutPath;
+            });
+            var layoutView = CreateView(v =>
+            {
+                actual = v.IsSectionDefined("foo");
+            });
+
+            // Act
+            await view.RenderAsync(CreateViewContext(layoutView));
+
+            // Assert
+            Assert.Equal(false, actual);
+        }
+
+        [Fact]
+        public async Task IsSectionDefined_ReturnsTrueIfSectionDefined()
+        {
+            // Arrange
+            bool? actual = null;
+            var view = CreateView(v =>
+            {
+                v.DefineSection("foo", new HelperResult(writer => { }));
+                v.Layout = LayoutPath;
+            });
+            var layoutView = CreateView(v =>
+            {
+                actual = v.IsSectionDefined("foo");
+            });
+
+            // Act
+            await view.RenderAsync(CreateViewContext(layoutView));
+
+            // Assert
+            Assert.Equal(true, actual);
+        }
+
         public static RazorView CreateView(Action<RazorView> executeAction)
         {
             var view = new Mock<RazorView> { CallBase = true };