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Fix #12661 Null Reference Exception: System.Windows.Forms.TabControl.<WmSelChange> #12683

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merged 5 commits into from
Jan 8, 2025
Merged

Fix #12661 Null Reference Exception: System.Windows.Forms.TabControl.<WmSelChange> #12683

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a1e2cb8
Fix issue 12661 and add unit test
John-Qiao Dec 25, 2024
43f7faa
Updated the unit test code lines to resolve the conversations from Tanya
John-Qiao Dec 26, 2024
5fe5e8b
Updated the BeginInvoke delegate in WmSelChange()
John-Qiao Jan 7, 2025
e5f9957
Removed that TabControl_WmSelChange_AccessibilityObjectNotCreated_NoA…
John-Qiao Jan 7, 2025
098eabe
Removed the unnecessary code lines from TabControlTests.cs file.
John-Qiao Jan 8, 2025
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9 changes: 8 additions & 1 deletion src/System.Windows.Forms/src/System/Windows/Forms/Controls/TabControl/TabControl.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -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
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65 changes: 65 additions & 0 deletions src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/TabControlTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5703,8 +5703,73 @@ 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();
}

[WinFormsFact]
public void TabControl_WmSelChange_AccessibilityObjectNotCreated_NoAutomationEventRaised()
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{
using TabControl tabControl = new();
using SubTabPage tabPage = new();
tabControl.SelectedTab = tabPage;
tabControl.SelectedIndex = 1;

var automationEventRaised = false;
tabPage.TabAccessibilityObject = new TabAccessibilityObject
{
RaiseAutomationEventAction = () => automationEventRaised = true
};

tabControl.TestAccessor().Dynamic.WmSelChange();

Application.DoEvents();
Thread.Sleep(100);

automationEventRaised.Should().BeFalse();
}

public class TabAccessibilityObject
{
public Action RaiseAutomationEventAction { get; set; }
public void RaiseAutomationEvent(UIA_EVENT_ID eventId)
{
RaiseAutomationEventAction?.Invoke();
}
}

public enum UIA_EVENT_ID
{
UIA_SelectionItem_ElementSelectedEventId,
UIA_AutomationFocusChangedEventId
}

private class SubTabPage : TabPage
{
public TabAccessibilityObject TabAccessibilityObject { get; set; }
}

private class NullTextTabPage : TabPage
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