Fix #12661 Null Reference Exception: System.Windows.Forms.TabControl.…

…<WmSelChange> (#12683) * Fix issue 12661 and add unit test * Updated the unit test code lines to resolve the conversations from Tanya * Updated the BeginInvoke delegate in WmSelChange() * Removed that TabControl_WmSelChange_AccessibilityObjectNotCreated_NoAutomationEventRaised() test * Removed the unnecessary code lines from TabControlTests.cs file.
dotnet · Jan 8, 2025 · 87bfb04 · 87bfb04
1 parent a3da2c9
commit 87bfb04
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diff --git a/src/System.Windows.Forms/src/System/Windows/Forms/Controls/TabControl/TabControl.cs b/src/System.Windows.Forms/src/System/Windows/Forms/Controls/TabControl/TabControl.cs
@@ -1957,7 +1957,14 @@ private bool WmSelChange()
             if (IsAccessibilityObjectCreated && SelectedTab?.ParentInternal is TabControl)
             {
                 SelectedTab.TabAccessibilityObject.RaiseAutomationEvent(UIA_EVENT_ID.UIA_SelectionItem_ElementSelectedEventId);
-                BeginInvoke((MethodInvoker)(() => SelectedTab.TabAccessibilityObject.RaiseAutomationEvent(UIA_EVENT_ID.UIA_AutomationFocusChangedEventId)));
+                BeginInvoke((MethodInvoker)(() =>
+                {
+                    if (IsAccessibilityObjectCreated && SelectedTab?.ParentInternal is TabControl &&
+                         !SelectedTab.IsDisposed && SelectedTab.TabAccessibilityObject is not null)
+                    {
+                        SelectedTab.TabAccessibilityObject.RaiseAutomationEvent(UIA_EVENT_ID.UIA_AutomationFocusChangedEventId);
+                    }
+                }));
             }
         }
         else

diff --git a/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/TabControlTests.cs b/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/TabControlTests.cs
@@ -5703,6 +5703,33 @@ public void TabControl_Invokes_SetToolTip_IfExternalToolTipIsSet()
         Assert.Equal(text, actual);
     }
 
+    [WinFormsFact]
+    public void TabControl_WmSelChange_SelectedTabIsNull_DoesNotThrowException()
+    {
+        using Form form = new();
+        using TabControl control = new();
+        using TabPage page1 = new("text1");
+        control.TabPages.Add(page1);
+        _ = control.AccessibilityObject;
+
+        form.Controls.Add(control);
+        form.Show();
+        control.SelectedIndex = 0;
+
+        Action act = () => control.TestAccessor().Dynamic.WmSelChange();
+        act.Should().NotThrow();
+
+        control.TabPages.Clear();
+
+        var exception = Record.Exception(() =>
+        {
+            Application.DoEvents();
+            Thread.Sleep(100);
+        });
+
+        exception.Should().BeNull();
+    }
+
     private class SubTabPage : TabPage
     {
     }