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Add InternalRaiseAutomationNotification in WmDateChanged of the MonthCalendar #13707

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Add InternalRaiseAutomationNotification in WmDateChanged of the MonthCalendar #13707

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804c36e
Add InternalRaiseAutomationNotification in WmDateChanged of the Month…
LeafShi1 Jul 16, 2025
553996e
Add switch EnableMonthCalendarAutomationNotification
LeafShi1 Jul 17, 2025
dbac5c4
Update src/System.Windows.Forms.Primitives/src/System/LocalAppContext…
LeafShi1 Jul 21, 2025
6211a11
Focus the MonthCanlendar when select date changed
Jul 22, 2025
728b2c6
Removing extra changes
Jul 22, 2025
acb2d59
Add NotifyWinEvent in MonthCalendar
LeafShi1 Jul 23, 2025
c1aa344
Add MSAA focus event in OnGotFocus
LeafShi1 Aug 7, 2025
3d5ae61
Add handle check before invoke PInvoke.NotifyWinEvent
LeafShi1 Sep 24, 2025
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Add NotifyWinEvent in MonthCalendar
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@LeafShi1
LeafShi1 committed Jul 23, 2025
commit acb2d5933d571cc36fbb99d4caad8d5c0be5dd56
16 changes: 13 additions & 3 deletions src/System.Windows.Forms/System/Windows/Forms/Controls/MonthCalendar/MonthCalendar.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2063,9 +2063,9 @@ private unsafe void WmDateChanged(ref Message m)
_selectionStart = start;
_selectionEnd = end;

AccessibilityNotifyClients(AccessibleEvents.Focus, -1);
AccessibilityNotifyClients(AccessibleEvents.NameChange, -1);
AccessibilityNotifyClients(AccessibleEvents.ValueChange, -1);
NotifyWinEvent(AccessibleEvents.Focus);
NotifyWinEvent(AccessibleEvents.NameChange);
NotifyWinEvent(AccessibleEvents.ValueChange);

// We should use the Date for comparison in this case. The user can work in the calendar only with dates,
// while the minimum / maximum date can contain the date and custom time, which, when comparing Ticks,
Expand Down Expand Up @@ -2095,6 +2095,16 @@ private unsafe void WmDateChanged(ref Message m)
OnDateChanged(new DateRangeEventArgs(start, end));
}

private void NotifyWinEvent(AccessibleEvents accessibleEvent)
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Can this throw potentially and with that regress exiting scenarios?

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The original method AccessibilityNotifyClients(...) internally checks the AppContextSwitches.NoClientNotifications flag. If this flag is set to true, it calls NotifyWinEvent(...); otherwise, it does nothing:

winforms/src/System.Windows.Forms/System/Windows/Forms/Control.cs

Lines 4227 to 4233 in 5a9fb88

protected void AccessibilityNotifyClients(AccessibleEvents accEvent, int objectID, int childID)
{
if (IsHandleCreated && AppContextSwitches.NoClientNotifications)
{
PInvoke.NotifyWinEvent((uint)accEvent, this, objectID, childID + 1);
}
}

Since AppContextSwitches.NoClientNotifications defaults to false, the system event is never raised, which causes screen readers like NVDA to miss updates from MonthCalendar.

Unfortunately, this method is protected and not overridable, and enabling the switch globally would affect all controls—not just MonthCalendar—which could introduce regressions elsewhere.

To resolve this, I replaced the call with a direct invocation of NotifyWinEvent(...), and added a handle check to ensure safety:

private void NotifyWinEvent(AccessibleEvents accessibleEvent)
{
    try
    {
        if (this.IsHandleCreated)
        {
            PInvoke.NotifyWinEvent(
                (uint)accessibleEvent,
                this,
                (int)OBJECT_IDENTIFIER.OBJID_CLIENT,
                (int)PInvoke.CHILDID_SELF
            );
        }
    }
    catch (Exception ex)
    {
        Debug.WriteLine($"NotifyWinEvent failed: {ex.Message}");
    }
}

This ensures that NVDA receives the necessary accessibility events without relying on global switches, and avoids potential exceptions by validating the control’s handle.

{
PInvoke.NotifyWinEvent(
(uint)accessibleEvent,
this,
(int)OBJECT_IDENTIFIER.OBJID_CLIENT,
(int)PInvoke.CHILDID_SELF
);
}

/// <summary>
/// Handles the MCN_GETDAYSTATE notification by returning an array of bitmasks, one entry per month,
/// that specifies which dates to display in bold.
Expand Down