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//---------------------------------------------------------------------------
//
// <copyright file="Accessible.cs" company="Microsoft">
// Copyright (C) Microsoft Corporation. All rights reserved.
// </copyright>
//
//
// Description: Wraps some of IAccessible to support Focus and top-level window creates
//
// History:
// 06/02/2003 : BrendanM Ported to WCP
//
//---------------------------------------------------------------------------
using System.Windows.Automation;
using System;
using Accessibility;
using System.Text;
using System.Diagnostics;
using MS.Win32;
// PRESHARP: In order to avoid generating warnings about unkown message numbers and unknown pragmas.
#pragma warning disable 1634, 1691
namespace MS.Internal.Automation
{
internal class Accessible
{
internal Accessible(IAccessible acc, object child)
{
Debug.Assert(acc != null, "null IAccessible");
_acc = acc;
_child = child;
}
// Create an Accessible object; may return null
internal static Accessible Create( IntPtr hwnd, int idObject, int idChild )
{
IAccessible acc = null;
object child = null;
if( UnsafeNativeMethods.AccessibleObjectFromEvent( hwnd, idObject, idChild, ref acc, ref child ) != 0 /*S_OK*/ || acc == null )
return null;
// Per SDK must use the ppacc and pvarChild from AccessibleObjectFromEvent
// to access information about this UI element.
return new Accessible( acc, child );
}
internal int State
{
get
{
try
{
return (int)_acc.get_accState(_child);
}
catch (Exception e)
{
if (IsCriticalMSAAException(e))
// PRESHARP will flag this as a warning 56503/6503: Property get methods should not throw exceptions
// Since this Property is internal, we CAN throw an exception
#pragma warning suppress 6503
throw;
return UnsafeNativeMethods.STATE_SYSTEM_UNAVAILABLE;
}
}
}
internal IntPtr Window
{
get
{
if (_hwnd == IntPtr.Zero)
{
try
{
if (UnsafeNativeMethods.WindowFromAccessibleObject(_acc, ref _hwnd) != 0/*S_OK*/)
{
_hwnd = IntPtr.Zero;
}
}
catch( Exception e )
{
if (IsCriticalMSAAException(e))
// PRESHARP will flag this as a warning 56503/6503: Property get methods should not throw exceptions
// Since this Property is internal, we CAN throw an exception
#pragma warning suppress 6503
throw;
_hwnd = IntPtr.Zero;
}
}
return _hwnd;
}
}
// miscellaneous functions used with Accessible
internal static bool CompareClass(IntPtr hwnd, string szClass)
{
return ProxyManager.GetClassName(NativeMethods.HWND.Cast(hwnd)) == szClass;
}
internal static bool IsComboDropdown(IntPtr hwnd)
{
return CompareClass(hwnd, "ComboLBox");
}
internal static bool IsStatic(IntPtr hwnd)
{
return CompareClass(hwnd, "Static");
}
private bool IsCriticalMSAAException(Exception e)
{
// Some OLEACC proxies produce out-of-memory for non-critical reasons:
// notably, the treeview proxy will raise this if the target HWND no longer exists,
// GetWindowThreadProcessID fails and it therefore won't be able to allocate shared
// memory in the target process, so it incorrectly assumes OOM.
// Some Native impls (media player) return E_POINTER, which COM Interop translates
// into NullRefException; need to ignore those too.
// should ignore those
return !(e is OutOfMemoryException)
&& !(e is NullReferenceException)
&& Misc.IsCriticalException(e);
}
private IntPtr _hwnd;
private IAccessible _acc;
private Object _child;
}
}
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