Fixes #768 by adding automation peer for TwoLineLabel

Changelog.md

@@ -8,6 +8,7 @@
   - [#758](../../issues/758) - Auto menu expanding not working for MenuItems with ItemSource binding
   - [#765](../../issues/765) - InRibbonGallery Resizing Issues
   - [#766](../../issues/766) - Resizing of InRibbonGallery in a DataTemplate does not work
+  - [#768](../../issues/768) - Accessibility Insights: "An onscreen element must not have a null"
 
 - ### Enhancements/Features
   - Many automation peers have been added and improved

Fluent.Ribbon/Automation/Peers/TwoLineLabelAutomationPeer.cs

@@ -0,0 +1,72 @@
+namespace Fluent.Automation.Peers
+{
+    using System.Collections.Generic;
+    using System.Windows.Automation.Peers;
+    using System.Windows.Automation.Provider;
+    using System.Windows.Controls;
+
+    /// <summary>
+    /// <see cref="AutomationPeer"/> for <see cref="TwoLineLabel"/>.
+    /// </summary>
+    public class TwoLineLabelAutomationPeer : FrameworkElementAutomationPeer
+    {
+        /// <summary>
+        /// Constructor.
+        /// </summary>
+        /// <param name="owner">Owner of the AutomationPeer.</param>
+        public TwoLineLabelAutomationPeer(TwoLineLabel owner)
+            : base(owner)
+        {
+        }
+
+        /// <summary>
+        /// <see cref="AutomationPeer.GetChildrenCore"/>
+        /// </summary>
+        protected override List<AutomationPeer> GetChildrenCore()
+        {
+            return null;
+        }
+
+        /// <summary>
+        /// <see cref="AutomationPeer.GetAutomationControlTypeCore"/>
+        /// </summary>
+        protected override AutomationControlType GetAutomationControlTypeCore()
+        {
+            return AutomationControlType.Text;
+        }
+
+        /// <summary>
+        /// <see cref="AutomationPeer.GetClassNameCore"/>
+        /// </summary>
+        /// <returns></returns>
+        protected override string GetClassNameCore()
+        {
+            return "TwoLineLabel";
+        }
+
+        /// <inheritdoc />
+        protected override string GetNameCore()
+        {
+            return ((TwoLineLabel)this.Owner).Text;
+        }
+
+        /// <summary>
+        /// <see cref="AutomationPeer.IsControlElementCore"/>
+        /// </summary>
+        protected override bool IsControlElementCore()
+        {
+            // Return false if TwoLineLabel is part of a ControlTemplate, otherwise return the base method
+            var tb = (TwoLineLabel)this.Owner;
+            var templatedParent = tb.TemplatedParent;
+
+            // If the templatedParent is a ContentPresenter, this TextBlock is generated from a DataTemplate
+            if (templatedParent == null
+                || templatedParent is ContentPresenter)
+            {
+                return base.IsControlElementCore();
+            }
+
+            return false;
+        }
+    }
+}

Fluent.Ribbon/Controls/TwoLineLabel.cs

@@ -4,6 +4,7 @@ namespace Fluent
     using System;
     using System.ComponentModel;
     using System.Windows;
+    using System.Windows.Automation.Peers;
     using System.Windows.Controls;
     using System.Windows.Markup;
     using Fluent.Internal.KnownBoxes;
@@ -124,6 +125,9 @@ public override void OnApplyTemplate()
             this.UpdateTextRun();
         }
 
+        /// <inheritdoc />
+        protected override AutomationPeer OnCreateAutomationPeer() => new Fluent.Automation.Peers.TwoLineLabelAutomationPeer(this);
+
         #endregion
 
         #region Event handling