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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
//
//
//
// Description:
// Accessibility event map classes are used to determine if, and how many
// listeners there are for events and property changes.
//
//
using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Automation;
using System.Windows.Automation.Peers;
using System.Windows.Threading;
using SR=MS.Internal.PresentationCore.SR;
namespace MS.Internal.Automation
{
// Manages the event map that is used to determine if there are Automation
// clients interested in specific events.
internal static class EventMap
{
private class EventInfo
{
internal EventInfo()
{
NumberOfListeners = 1;
}
internal int NumberOfListeners;
}
// Never inline, as we don't want to unnecessarily link the automation DLL.
[System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.NoInlining)]
private static bool IsKnownLegacyEvent(int id)
{
if ( id == AutomationElementIdentifiers.ToolTipOpenedEvent.Id
|| id == AutomationElementIdentifiers.ToolTipClosedEvent.Id
|| id == AutomationElementIdentifiers.MenuOpenedEvent.Id
|| id == AutomationElementIdentifiers.MenuClosedEvent.Id
|| id == AutomationElementIdentifiers.AutomationFocusChangedEvent.Id
|| id == InvokePatternIdentifiers.InvokedEvent.Id
|| id == SelectionItemPatternIdentifiers.ElementAddedToSelectionEvent.Id
|| id == SelectionItemPatternIdentifiers.ElementRemovedFromSelectionEvent.Id
|| id == SelectionItemPatternIdentifiers.ElementSelectedEvent.Id
|| id == SelectionPatternIdentifiers.InvalidatedEvent.Id
|| id == TextPatternIdentifiers.TextSelectionChangedEvent.Id
|| id == TextPatternIdentifiers.TextChangedEvent.Id
|| id == AutomationElementIdentifiers.AsyncContentLoadedEvent.Id
|| id == AutomationElementIdentifiers.AutomationPropertyChangedEvent.Id
|| id == AutomationElementIdentifiers.StructureChangedEvent.Id
|| id == SynchronizedInputPatternIdentifiers.InputReachedTargetEvent?.Id
|| id == SynchronizedInputPatternIdentifiers.InputReachedOtherElementEvent?.Id
|| id == SynchronizedInputPatternIdentifiers.InputDiscardedEvent?.Id)
{
return true;
}
return false;
}
// Never inline, as we don't want to unnecessarily link the automation DLL.
[System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.NoInlining)]
private static bool IsKnownNewEvent(int id)
{
if ( id == AutomationElementIdentifiers.LiveRegionChangedEvent?.Id
|| id == AutomationElementIdentifiers.NotificationEvent?.Id
|| id == AutomationElementIdentifiers.ActiveTextPositionChangedEvent?.Id)
{
return true;
}
return false;
}
// Never inline, as we don't want to unnecessarily link the automation DLL.
[System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.NoInlining)]
private static bool IsKnownEvent(int id)
{
if (IsKnownLegacyEvent(id) ||
(!AccessibilitySwitches.UseNetFx47CompatibleAccessibilityFeatures && IsKnownNewEvent(id)))
{
return true;
}
return false;
}
// Never inline, as we don't want to unnecessarily link the automation DLL.
[System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.NoInlining)]
private static AutomationEvent GetRegisteredEventObjectHelper(AutomationEvents eventId)
{
AutomationEvent eventObject = null;
switch(eventId)
{
case AutomationEvents.ToolTipOpened: eventObject = AutomationElementIdentifiers.ToolTipOpenedEvent; break;
case AutomationEvents.ToolTipClosed: eventObject = AutomationElementIdentifiers.ToolTipClosedEvent; break;
case AutomationEvents.MenuOpened: eventObject = AutomationElementIdentifiers.MenuOpenedEvent; break;
case AutomationEvents.MenuClosed: eventObject = AutomationElementIdentifiers.MenuClosedEvent; break;
case AutomationEvents.AutomationFocusChanged: eventObject = AutomationElementIdentifiers.AutomationFocusChangedEvent; break;
case AutomationEvents.InvokePatternOnInvoked: eventObject = InvokePatternIdentifiers.InvokedEvent; break;
case AutomationEvents.SelectionItemPatternOnElementAddedToSelection: eventObject = SelectionItemPatternIdentifiers.ElementAddedToSelectionEvent; break;
case AutomationEvents.SelectionItemPatternOnElementRemovedFromSelection: eventObject = SelectionItemPatternIdentifiers.ElementRemovedFromSelectionEvent; break;
case AutomationEvents.SelectionItemPatternOnElementSelected: eventObject = SelectionItemPatternIdentifiers.ElementSelectedEvent; break;
case AutomationEvents.SelectionPatternOnInvalidated: eventObject = SelectionPatternIdentifiers.InvalidatedEvent; break;
case AutomationEvents.TextPatternOnTextSelectionChanged: eventObject = TextPatternIdentifiers.TextSelectionChangedEvent; break;
case AutomationEvents.TextPatternOnTextChanged: eventObject = TextPatternIdentifiers.TextChangedEvent; break;
case AutomationEvents.AsyncContentLoaded: eventObject = AutomationElementIdentifiers.AsyncContentLoadedEvent; break;
case AutomationEvents.PropertyChanged: eventObject = AutomationElementIdentifiers.AutomationPropertyChangedEvent; break;
case AutomationEvents.StructureChanged: eventObject = AutomationElementIdentifiers.StructureChangedEvent; break;
case AutomationEvents.InputReachedTarget: eventObject = SynchronizedInputPatternIdentifiers.InputReachedTargetEvent; break;
case AutomationEvents.InputReachedOtherElement: eventObject = SynchronizedInputPatternIdentifiers.InputReachedOtherElementEvent; break;
case AutomationEvents.InputDiscarded: eventObject = SynchronizedInputPatternIdentifiers.InputDiscardedEvent; break;
case AutomationEvents.LiveRegionChanged: eventObject = AutomationElementIdentifiers.LiveRegionChangedEvent; break;
case AutomationEvents.Notification: eventObject = AutomationElementIdentifiers.NotificationEvent; break;
case AutomationEvents.ActiveTextPositionChanged: eventObject = AutomationElementIdentifiers.ActiveTextPositionChangedEvent; break;
default:
throw new ArgumentException(SR.Automation_InvalidEventId, "eventId");
}
if ((eventObject != null) && (!_eventsTable.ContainsKey(eventObject.Id)))
{
eventObject = null;
}
return (eventObject);
}
internal static void AddEvent(int idEvent)
{
// to avoid unbound memory allocations,
// register only events that we recognize
if (IsKnownEvent(idEvent))
{
bool firstEvent = false;
lock (_lock)
{
if (_eventsTable == null)
{
_eventsTable = new Dictionary<int, EventInfo>(20);
firstEvent = true;
}
if (_eventsTable.TryGetValue(idEvent, out EventInfo info))
{
info.NumberOfListeners++;
}
else
{
_eventsTable[idEvent] = new EventInfo();
}
}
// notify PresentationSources (outside the lock) when the number
// of listeners becomes non-zero
if (firstEvent)
{
NotifySources();
}
}
}
internal static void RemoveEvent(int idEvent)
{
lock (_lock)
{
if (_eventsTable != null)
{
// Decrement the count of listeners for this event
if (_eventsTable.TryGetValue(idEvent, out EventInfo info))
{
// Update or remove the entry based on remaining listeners
info.NumberOfListeners--;
if (info.NumberOfListeners <= 0)
{
_eventsTable.Remove(idEvent);
// If no more entries exist kill the table
if (_eventsTable.Count == 0)
{
_eventsTable = null;
}
}
}
}
}
}
// Unlike GetRegisteredEvent below,
// HasRegisteredEvent does NOT cause automation DLLs loading
internal static bool HasRegisteredEvent(AutomationEvents eventId)
{
lock (_lock)
{
if (_eventsTable != null && _eventsTable.Count != 0)
{
return (GetRegisteredEventObjectHelper(eventId) != null);
}
}
return (false);
}
internal static AutomationEvent GetRegisteredEvent(AutomationEvents eventId)
{
lock (_lock)
{
if (_eventsTable != null && _eventsTable.Count != 0)
{
return (GetRegisteredEventObjectHelper(eventId));
}
}
return (null);
}
internal static bool HasListeners
{
get { return (_eventsTable != null); }
}
// Most automation clients send WM_GETOBJECT messages to our hwnd(s).
// We rely on these to add the top-level peers to the LayoutManager's
// AutomationEvents list, so that the automation tree stays in sync with
// the visual tree. But some "clients" merely add WinEvent hooks to
// intercept automation messages, and don't send WM_GETOBJECT messages.
// This can lead to crashes (with System.Windows.Automation.ElementNotAvailableException) as follows:
// 1. external process installs a WinEvent hook
// 2. WPF app opens a popup. PopupSecurityHelper.ForceMsaaToUiaBridge
// detects the hook, creates a peer, informs uiacore.
// 3. uiacore registers for automation events, calling EventMap.AddEvent
// 4. elements throughout the app (on any thread) create peers, thinking
// that there is interest in the relevant automation events
// (EventMap.HasRegisteredEvent returns true).
// 5. after visual tree changes, the automation tree is not fixed up fully
// 6. some automation code uses outdated information and throws
// an exception or makes bad decisions that lead to problems later
// [In some cases, TreeViewItems get recycled to display different data,
// but the corresponding TreeViewItemAutomationPeers don't always get
// fixed up to refer to a different EventSource (TreeViewDataItemAutomationPeer).
// A subsequent UpdatePeer (induced by changing IsEnabled) walks down
// the wrong path, finds a stale data item peer, and throws ElementNotFoundException.]
//
// To mitigate this, ensure that all top-level peers get added to the
// AutomationEvents list whenever there are any event listeners. This
// has two parts:
// a. new top-level elements (HwndSource.RootVisual) check for listeners
// and add themselves to the list
// b. when the listener count becomes non-zero, add existing top-level
// elements to the list
// This strategy is much cheaper than checking something each time an
// element creates a peer (as in (4) above), but it will create a full
// automation tree for all windows, even those that don't have any
// elements that check for events. However, that's just what would
// happen in the presence of a full automation client that sends
// WM_GETOBJECT, so it's a cost we're already paying in the "normal" case.
//
// The following methods implement (b). See <see cref="HwndSource.RootVisual"/> for (a).
private static void NotifySources()
{
foreach (PresentationSource source in PresentationSource.CriticalCurrentSources)
{
if (!source.IsDisposed)
{
source.Dispatcher.BeginInvoke(DispatcherPriority.Normal, (DispatcherOperationCallback)(state =>
{
PresentationSource source = (PresentationSource)state;
if (source != null && !source.IsDisposed)
{
// setting the RootVisual to itself triggers the logic to
// add to the AutomationEvents list
source.RootVisual = source.RootVisual;
}
return null;
}), source);
}
}
}
private static Dictionary<int, EventInfo> _eventsTable; // key=event id, data=listener count
private readonly static object _lock = new object();
}
}
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