Code:
/ DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / AccessibleTech / longhorn / Automation / UIAutomationClient / MS / Internal / Automation / InvokeHandlers.cs / 1 / InvokeHandlers.cs
//---------------------------------------------------------------------------- // //// Copyright (C) Microsoft Corporation. All rights reserved. // // // // Description: class which defines the delegates used to invoke the client event handlers // // History: // 06/17/2003 : [....] Ported to WCP // //--------------------------------------------------------------------------- using System; using System.Windows.Automation; using System.ComponentModel; using System.Threading; using System.Diagnostics; namespace MS.Internal.Automation { // Temp class used to bundle focus event time along with the usual // focus change information. The InvokeHandler code below that dispatches // focus change events checks the time, and drops any events thta have // a timestamp that is earlier than the most recently dispatched event. // (This avoids race conditions from events from WinEvents and events from UIA, // which arrive on different threads, and which can drift during their processing, // since winevents get scope-checked - slow - as part of their processing before // being queued, whereas UIA events are just queued up. The key issue with any // timestamp checking is that it happens *after* the two streams of events have // been merged - otherwise they could just drift again. This is the case here, // since the InvokeHandler code is called by the callbackqueue, which services // both these types of events.) // // This code is "temp" - there's a work item to remove AsyncOperations, and // removing that should result in a cleaner solution to passing the eventTime // around, perhaps passing it directly to the InvokeHandlers method instead of // tunnelling it into a 'wrapped' AutomationFocusChangedEventArgs. internal class InternalAutomationFocusChangedEventArgs : AutomationFocusChangedEventArgs { internal AutomationFocusChangedEventArgs _args; internal uint _eventTime; internal InternalAutomationFocusChangedEventArgs(int idObject, int idChild, uint eventTime) : base(idObject, idChild) { _args = new AutomationFocusChangedEventArgs(idObject, idChild); _eventTime = eventTime; } }; // This class manages dispatching events to the different types of // UIA event delegates internal static class InvokeHandlers { //----------------------------------------------------- // // Internal Methods // //----------------------------------------------------- #region Internal Methods // The method that gets called from CallbackQueue's thread. Uses Post to invoke the callback on the proper thread. internal static void InvokeClientHandler(Delegate clientCallback, AutomationElement srcEl, AutomationEventArgs args) { try { if (args is AutomationPropertyChangedEventArgs) { ((AutomationPropertyChangedEventHandler)clientCallback)(srcEl, (AutomationPropertyChangedEventArgs)args); } else if (args is StructureChangedEventArgs) { ((StructureChangedEventHandler)clientCallback)(srcEl, (StructureChangedEventArgs)args); } else if (args is InternalAutomationFocusChangedEventArgs) { AutomationFocusChangedEventArgs realArgs = ((InternalAutomationFocusChangedEventArgs)args)._args; // For focus events, check that the event is actually more recent than the last one (see note at top of file). // Since the timestamps can wrap around, subtract and measure the delta instead of just comparing them. // Any events that appear to have taken place within the 5 seconds before the last event we got will be ignored. // (Because of wraparound, certain before- and after- time spans share the same deltas; 5000ms before has the // same value as MAXUINT-5000ms after. Since we're just trying to filter out very recent event race conditions, // confine this test to a small window, just the most recent 5 seconds. That means you'd have to wait a *very* // long time without any focus changes before getting a false positive here.) uint eventTime = ((InternalAutomationFocusChangedEventArgs)args)._eventTime; if (_lastFocusEventTime != 0) { uint delta = _lastFocusEventTime - eventTime; // Exclude events that happend before the last one, but do allow any that happened "at the same time", // (delta==0) since they likely actually happened after, but within the resolution of the event timer. if (delta < 5000 && delta != 0) { return; } } _lastFocusEventTime = eventTime; ((AutomationFocusChangedEventHandler)clientCallback)(srcEl, realArgs); } else { ((AutomationEventHandler)clientCallback)(srcEl, args); } } catch (Exception e) { if (Misc.IsCriticalException(e)) throw; // Since we can't predict what exceptions an outside client might throw intentionally ignore all } } #endregion Internal Methods //------------------------------------------------------ // // Internal Fields // //----------------------------------------------------- #region Internal Fields internal static uint _lastFocusEventTime; #endregion Internal Fields } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. All rights reserved.
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