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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.
using System.Globalization;
using System.Windows.Forms.Automation;
using System.Windows.Forms.Primitives;
using Windows.Win32.System.Variant;
using Windows.Win32.UI.Accessibility;
namespace System.Windows.Forms;
public partial class Control
{
/// <summary>
/// An implementation of AccessibleChild for use with Controls.
/// </summary>
public class ControlAccessibleObject : AccessibleObject, IOwnedObject<Control>
{
/// <summary>
/// Associated window handle (if any).
/// </summary>
private HWND _handle = HWND.Null;
/// <summary>
/// Used to lazily grab the owner control handle, if it hasn't been created yet.
/// </summary>
private bool _getOwnerControlHandle;
private readonly WeakReference<Control> _ownerControl;
public ControlAccessibleObject(Control ownerControl)
: this(ownerControl, (int)OBJECT_IDENTIFIER.OBJID_CLIENT)
{
}
internal ControlAccessibleObject(Control ownerControl, int accObjId)
{
// Must set AccesibleObjectId *before* setting the Handle property as it calls UseStdAccessibleObjects()
// which needs the Id.
AccessibleObjectId = accObjId;
_ownerControl = new(ownerControl.OrThrowIfNull());
if (ownerControl.IsHandleCreated)
{
Handle = ownerControl.Handle;
}
else
{
// If the owner control doesn't have a valid handle, wait until there is either
// a request to create it, or the owner control creates a handle, which will
// be set via Handle property.
_getOwnerControlHandle = true;
}
}
private protected override string AutomationId
=> this.TryGetOwnerAs(out Control? owner) ? owner.Name : string.Empty;
// If the control is used as an item of a ToolStrip via ToolStripControlHost,
// its accessible object should provide info about the owning ToolStrip and items-siblings
// to build a correct ToolStrip accessibility tree.
internal override IRawElementProviderFragment.Interface? FragmentNavigate(NavigateDirection direction)
{
if (!this.TryGetOwnerAs(out Control? owner) || owner.ToolStripControlHost is not ToolStripControlHost host)
{
return base.FragmentNavigate(direction);
}
return direction is NavigateDirection.NavigateDirection_Parent
or NavigateDirection.NavigateDirection_PreviousSibling
or NavigateDirection.NavigateDirection_NextSibling
? host.AccessibilityObject.FragmentNavigate(direction)
: base.FragmentNavigate(direction);
}
/// <summary>
/// For container controls only, return array of child controls sorted into
/// tab index order. This gets applies to the list of child accessible objects
/// as returned by the system, so that we can present a meaningful order to
/// the user. The system defaults to z-order, which is bad for us because
/// that is usually the reverse of tab order!
/// </summary>
internal override int[]? GetSysChildOrder()
=> this.TryGetOwnerAs(out Control? owner) && owner.GetStyle(ControlStyles.ContainerControl)
? owner.GetChildWindowsInTabOrder()
: base.GetSysChildOrder();
/// <summary>
/// Perform custom navigation between parent/child/sibling accessible objects,
/// using tab index order as the guide, rather than letting the system default
/// behavior do navigation based on z-order.
///
/// For a container control and its child controls, the accessible object tree
/// looks like this...
///
/// [client area of container]
/// [non-client area of child #1]
/// [random non-client elements]
/// [client area of child #1]
/// [random non-client elements]
/// [non-client area of child #2]
/// [random non-client elements]
/// [client area of child #2]
/// [random non-client elements]
/// [non-client area of child #3]
/// [random non-client elements]
/// [client area of child #3]
/// [random non-client elements]
///
/// We need to intercept first-child / last-child navigation from the container's
/// client object, and next-sibling / previous-sibling navigation from each child's
/// non-client object. All other navigation operations must be allowed to fall back
/// on the system's default behavior (provided by OLEACC.DLL).
///
/// When combined with the re-ordering behavior of GetSysChildOrder() above, this
/// allows us to present the end user with the illusion of accessible objects in
/// tab index order, even though the system behavior only supports z-order.
/// </summary>
internal override bool GetSysChild(AccessibleNavigation navdir, out AccessibleObject? accessibleObject)
{
if (!this.TryGetOwnerAs(out Control? owner))
{
return base.GetSysChild(navdir, out accessibleObject);
}
// Clear the out parameter
accessibleObject = null;
// Get the owning control's parent, if it has one
Control? parentControl = owner.ParentInternal;
// ctrls[index] will indicate the control at the destination of this navigation operation.
int index = -1;
Control[]? ctrls = null;
// Now handle any 'appropriate' navigation requests.
switch (navdir)
{
case AccessibleNavigation.FirstChild:
if (IsClientObject)
{
ctrls = owner.GetChildControlsInTabOrder(handleCreatedOnly: true);
index = 0;
}
break;
case AccessibleNavigation.LastChild:
if (IsClientObject)
{
ctrls = owner.GetChildControlsInTabOrder(true);
index = ctrls.Length - 1;
}
break;
case AccessibleNavigation.Previous:
if (IsNonClientObject && parentControl is not null)
{
ctrls = parentControl.GetChildControlsInTabOrder(true);
index = Array.IndexOf(ctrls, owner);
if (index != -1)
{
--index;
}
}
break;
case AccessibleNavigation.Next:
if (IsNonClientObject && parentControl is not null)
{
ctrls = parentControl.GetChildControlsInTabOrder(true);
index = Array.IndexOf(ctrls, owner);
if (index != -1)
{
++index;
}
}
break;
}
// Unsupported navigation operation for this object, or unexpected error.
// Return false to force fall back on default system navigation behavior.
if (ctrls is null || ctrls.Length == 0)
{
return false;
}
// If ctrls[index] is a valid control, return its non-client accessible object.
// If index is invalid, return null pointer meaning "end of list reached".
if (index >= 0 && index < ctrls.Length)
{
accessibleObject = ctrls[index].NcAccessibilityObject;
}
// Return true to use the found accessible object and block default system behavior
return true;
}
public override string? DefaultAction => Owner?.AccessibleDefaultActionDescription ?? base.DefaultAction;
internal override bool CanGetDefaultActionInternal => IsInternal && Owner?.AccessibleDefaultActionDescription is null;
/// <remarks>
/// <para>
/// This is used only if control supports <see cref="IAccessibleEx" />. We need to provide a unique ID.
/// Others are implementing this in the same manner. First item is static - <see cref="AccessibleObject.RuntimeIDFirstItem"/>).
/// Second item can be anything unique, Win32 uses <see cref="HWND"/>, we copied that.
/// </para>
/// </remarks>
/// <inheritdoc cref="AccessibleObject.RuntimeId" />
internal override int[] RuntimeId =>
[
RuntimeIDFirstItem,
(int)HandleInternal,
GetHashCode()
];
public override string? Description => Owner?.AccessibleDescription ?? base.Description;
internal override bool CanGetDescriptionInternal => IsInternal && Owner?.AccessibleDescription is null;
/// <summary>
/// Gets or sets the handle of the accessible object's associated <see cref="Owner"/> control.
/// </summary>
/// <value>
/// An <see cref="IntPtr"/> that represents the handle of the associated <see cref="Owner"/> control.
/// </value>
/// <remarks>
/// <para>
/// The value of the <see cref="Handle"/> property for the <see cref="ControlAccessibleObject"/> is equal to
/// the <see cref="Control.Handle"/> property of the <see cref="Owner"/> it is associated with.
/// </para>
/// </remarks>
public IntPtr Handle
{
get
{
if (_getOwnerControlHandle)
{
// We haven't gotten the associated Control handle yet, grab it now (this will create the
// Control's handle if it hasn't been created yet).
_getOwnerControlHandle = false;
_handle = Owner?.HWND ?? default;
}
return _handle;
}
set
{
if (_handle == value)
{
return;
}
_handle = (HWND)value;
_getOwnerControlHandle = false;
if (_handle.IsNull)
{
return;
}
// Create the Win32 standard accessible objects. We fall back to these in a number of code paths.
UseStdAccessibleObjects(_handle);
}
}
internal HWND HandleInternal => _handle;
public override string? Help
{
get
{
if (this.TryGetOwnerAs(out Control? owner)
&& owner.Events[s_queryAccessibilityHelpEvent] is QueryAccessibilityHelpEventHandler handler)
{
QueryAccessibilityHelpEventArgs args = new();
handler(Owner, args);
return args.HelpString;
}
return base.Help;
}
}
internal override bool CanGetHelpInternal =>
IsInternal
&& (!this.TryGetOwnerAs(out Control? owner)
|| owner.Events[s_queryAccessibilityHelpEvent] is not QueryAccessibilityHelpEventHandler);
public override string? KeyboardShortcut
{
get
{
// For controls, the default keyboard shortcut comes directly from the accessible
// name property. This matches the default behavior of OLEACC.DLL exactly.
char mnemonic = WindowsFormsUtils.GetMnemonic(TextLabel, false);
return (mnemonic == (char)0) ? null : $"Alt+{mnemonic}";
}
}
internal override bool CanGetKeyboardShortcutInternal => false;
public override string? Name
{
get
{
// Special case: If an explicit name has been set in the AccessibleName property, use that.
// Note: Any non-null value in AccessibleName overrides the default accessible name logic,
// even an empty string (this is the only way to *force* the accessible name to be blank).
if (this.TryGetOwnerAs(out Control? owner) && owner.AccessibleName is { } name)
{
return name;
}
// Otherwise just return the default label string, minus any mnemonics
return WindowsFormsUtils.TextWithoutMnemonics(TextLabel);
}
set
{
// If anyone tries to set the accessible name, just cache the value in the control's
// AccessibleName property. This value will then end up overriding the normal accessible
// name logic, until such time as AccessibleName is set back to null.
if (this.TryGetOwnerAs(out Control? owner))
{
owner.AccessibleName = value;
}
}
}
internal override bool CanGetNameInternal => false;
internal override bool CanSetNameInternal => false;
public override AccessibleObject? Parent => base.Parent;
// Determine the text that should be used to 'label' this control for accessibility purposes.
//
// Prior to Whidbey, we just called 'base.Name' to determine the accessible name. This would end up calling
// OLEACC.DLL to determine the name. The rules used by OLEACC.DLL are the same as what we now have below,
// except that OLEACC searches for preceding labels using z-order, and we want to search for labels using
// TabIndex order.
internal string? TextLabel
{
get
{
// If owning control allows, use its Text property - but only if that Text is not empty
if (this.TryGetOwnerAs(out Control? owner) && owner.GetStyle(ControlStyles.UseTextForAccessibility))
{
string text = owner.Text;
if (!string.IsNullOrEmpty(text))
{
return text;
}
}
// Otherwise use the text of the preceding Label control, if there is one
Label? previousLabel = PreviousLabel;
if (previousLabel is not null)
{
string text = previousLabel.Text;
if (!string.IsNullOrEmpty(text))
{
return text;
}
}
// This control has no discernable MSAA name - return an empty string to indicate 'nameless'.
return null;
}
}
/// <summary>
/// Gets the owner of the accessible object.
/// </summary>
/// <remarks>
/// <para>
/// The only time this will be null is if the owner has been garbage collected.
/// </para>
/// </remarks>
public Control? Owner => _ownerControl.TryGetTarget(out Control? owner) ? owner : null;
// Look for a label immediately preceeding this control in
// the tab order, and use its name for the accessible name.
//
// This method aims to emulate the equivalent behavior in OLEACC.DLL,
// but walking controls in TabIndex order rather than native z-order.
internal Label? PreviousLabel
{
get
{
// Try to get to the parent of this control.
if (!this.TryGetOwnerAs(out Control? owner) || owner.ParentInternal is not { } parent)
{
return null;
}
// Find this control's containing control
if (parent.GetContainerControl() is not ContainerControl container)
{
return null;
}
// Walk backwards through peer controls...
for (Control? previous = container.GetNextControl(owner, false);
previous is not null;
previous = container.GetNextControl(previous, false))
{
// Stop when we hit a Label (whether visible or invisible)
if (previous is Label label)
{
return label;
}
// Stop at any *visible* tab stop
if (previous.Visible && previous.TabStop)
{
break;
}
}
return null;
}
}
public override AccessibleRole Role
{
get
{
AccessibleRole role = Owner?.AccessibleRole ?? AccessibleRole.Default;
return role != AccessibleRole.Default ? role : base.Role;
}
}
public override int GetHelpTopic(out string? fileName)
{
if (!this.TryGetOwnerAs(out Control? owner)
|| owner.Events[s_queryAccessibilityHelpEvent] is not QueryAccessibilityHelpEventHandler handler)
{
return base.GetHelpTopic(out fileName);
}
QueryAccessibilityHelpEventArgs args = new();
handler(owner, args);
fileName = args.HelpNamespace;
int.TryParse(args.HelpKeyword, NumberStyles.Integer, CultureInfo.InvariantCulture, out int topic);
return topic;
}
internal override bool CanGetHelpTopicInternal =>
IsInternal
&& (!this.TryGetOwnerAs(out Control? owner)
|| owner.Events[s_queryAccessibilityHelpEvent] is not QueryAccessibilityHelpEventHandler);
public void NotifyClients(AccessibleEvents accEvent)
=> NotifyClients(accEvent, (int)OBJECT_IDENTIFIER.OBJID_CLIENT, 0);
public void NotifyClients(AccessibleEvents accEvent, int childID)
=> NotifyClients(accEvent, (int)OBJECT_IDENTIFIER.OBJID_CLIENT, childID);
public void NotifyClients(AccessibleEvents accEvent, int objectID, int childID)
{
if (HandleInternal.IsNull || LocalAppContextSwitches.NoClientNotifications)
{
return;
}
PInvoke.NotifyWinEvent(
(uint)accEvent,
new HandleRef<HWND>(Owner, HandleInternal),
objectID,
childID + 1);
}
/// <summary>
/// Raises the LiveRegionChanged UIA event.
/// </summary>
/// <remarks>
/// <para>
/// To make this method effective, the control must implement <see cref="IAutomationLiveRegion"/>
/// and its <see cref="IAutomationLiveRegion.LiveSetting"/> property must return either
/// <see cref="AutomationLiveSetting.Polite"/> or <see cref="AutomationLiveSetting.Assertive"/>.
/// </para>
/// </remarks>
/// <returns>True if operation succeeds, False otherwise.</returns>
public override bool RaiseLiveRegionChanged()
{
if (this.TryGetOwnerAs(out Control? owner))
{
return owner is not IAutomationLiveRegion
? throw new InvalidOperationException(SR.OwnerControlIsNotALiveRegion)
: RaiseAutomationEvent(UIA_EVENT_ID.UIA_LiveRegionChangedEventId);
}
return false;
}
internal override bool IsPatternSupported(UIA_PATTERN_ID patternId)
=> (this.TryGetOwnerAs(out Control? owner) && owner.SupportsUiaProviders && patternId == UIA_PATTERN_ID.UIA_LegacyIAccessiblePatternId)
|| base.IsPatternSupported(patternId);
internal override bool IsIAccessibleExSupported()
=> Owner is IAutomationLiveRegion || base.IsIAccessibleExSupported();
internal override VARIANT GetPropertyValue(UIA_PROPERTY_ID propertyID) =>
propertyID switch
{
UIA_PROPERTY_ID.UIA_ControlTypePropertyId
// "ControlType" value depends on owner's AccessibleRole value.
// See: docs/accessibility/accessible-role-controltype.md
=> (VARIANT)(int)AccessibleRoleControlTypeMap.GetControlType(Role),
UIA_PROPERTY_ID.UIA_IsEnabledPropertyId
=> Owner?.Enabled == true ? VARIANT.True : VARIANT.False,
UIA_PROPERTY_ID.UIA_IsKeyboardFocusablePropertyId when
Owner?.SupportsUiaProviders ?? false
=> (VARIANT)Owner.CanSelect,
UIA_PROPERTY_ID.UIA_LiveSettingPropertyId
=> Owner is IAutomationLiveRegion owner
? (VARIANT)(int)owner.LiveSetting
: base.GetPropertyValue(propertyID),
UIA_PROPERTY_ID.UIA_NativeWindowHandlePropertyId
=> UIAHelper.WindowHandleToVariant(Owner?.InternalHandle ?? HWND.Null),
_ => base.GetPropertyValue(propertyID)
};
internal override bool RaiseAutomationEvent(UIA_EVENT_ID eventId)
=> this.IsOwnerHandleCreated(out Control? _) && base.RaiseAutomationEvent(eventId);
internal override bool RaiseAutomationPropertyChangedEvent(UIA_PROPERTY_ID propertyId, VARIANT oldValue, VARIANT newValue)
=> this.IsOwnerHandleCreated(out Control? _)
&& base.RaiseAutomationPropertyChangedEvent(propertyId, oldValue, newValue);
internal override unsafe IRawElementProviderSimple* HostRawElementProvider
{
get
{
if (HandleInternal.IsNull)
{
return null;
}
PInvoke.UiaHostProviderFromHwnd(new HandleRef<HWND>(this, HandleInternal), out IRawElementProviderSimple* provider);
return provider;
}
}
// If the control is used as an item of a ToolStrip via ToolStripControlHost,
// its accessible object should provide info about the owning ToolStrip
// to build a correct ToolStrip accessibility tree.
private protected override IRawElementProviderFragmentRoot.Interface? ToolStripFragmentRoot =>
Owner?.ToolStripControlHost?.Owner?.AccessibilityObject;
public override string ToString()
=> $"{nameof(ControlAccessibleObject)}: Owner = {Owner?.ToString() ?? "null"}";
}
}
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