AccessibleObject.GetChild 方法
检索对应于指定索引的辅助性子级。
**命名空间:**System.Windows.Forms
**程序集:**System.Windows.Forms（在 system.windows.forms.dll 中）
语法
声明
Public Overridable Function GetChild ( _
index As Integer _
) As AccessibleObject
用法
Dim instance As AccessibleObject
Dim index As Integer
Dim returnValue As AccessibleObject
returnValue = instance.GetChild(index)
public virtual AccessibleObject GetChild (
int index
)
public:
virtual AccessibleObject^ GetChild (
int index
)
public AccessibleObject GetChild (
int index
)
public function GetChild (
index : int
) : AccessibleObject
参数
- index
辅助性子级的从零开始的索引。
返回值
AccessibleObject，表示与指定索引对应的辅助性子级。
备注
给继承者的说明 所有辅助性对象都必须支持该属性。如果没有重写方法，它将返回 空引用（在 Visual Basic 中为 Nothing）。在辅助性对象需要提供自定义辅助性子级时重写此方法。如果索引无效，则此方法应返回 空引用（在 Visual Basic 中为 Nothing）。重写此方法时，也必须重写 GetChildCount。
示例
下面的示例演示了如何创建一个具有辅助功能的图表控件，并使用 AccessibleObject 和 Control.ControlAccessibleObject 类来公开辅助性信息。该控件绘制两条带有图例的曲线。CreateAccessibilityInstance 方法使用从 ControlAccessibleObject 派生的 ChartControlAccessibleObject 类，为图表控件提供自定义辅助性信息。因为图表图例不是实际的基于 Control 的控件，而是由图表控件绘制的，所以它不提供任何内置的辅助性信息。因此，ChartControlAccessibleObject 类重写 GetChild 方法以返回 CurveLegendAccessibleObject（表示该图例各部分的辅助性信息）。当具有辅助功能的应用程序使用该控件时，该控件能提供必需的辅助性信息。
这段代码摘录演示了如何重写 GetChild 方法。有关完整的代码示例，请参见 AccessibleObject 类概述。
' Inner Class ChartControlAccessibleObject represents accessible information
' associated with the ChartControl.
' The ChartControlAccessibleObject is returned in the ' ChartControl.CreateAccessibilityInstance override.
Public Class ChartControlAccessibleObject
Inherits Control.ControlAccessibleObject
Private chartControl As ChartControl
Public Sub New(ctrl As ChartControl)
MyBase.New(ctrl)
chartControl = ctrl
End Sub 'New
' Get the role for the Chart. This is used by accessibility programs.
Public Overrides ReadOnly Property Role() As AccessibleRole
Get
Return System.Windows.Forms.AccessibleRole.Chart
End Get
End Property
' Get the state for the Chart. This is used by accessibility programs.
Public Overrides ReadOnly Property State() As AccessibleStates
Get
Return AccessibleStates.ReadOnly
End Get
End Property
' The CurveLegend objects are "child" controls in terms of accessibility so
' return the number of ChartLengend objects.
Public Overrides Function GetChildCount() As Integer
Return chartControl.Legends.Length
End Function
' Get the Accessibility object of the child CurveLegend idetified by index.
Public Overrides Function GetChild(index As Integer) As AccessibleObject
If index >= 0 And index < chartControl.Legends.Length Then
Return chartControl.Legends(index).AccessibilityObject
End If
Return Nothing
End Function
' Helper function that is used by the CurveLegend's accessibility object
' to navigate between sibiling controls. Specifically, this function is used in
' the CurveLegend.CurveLegendAccessibleObject.Navigate function.
Friend Function NavigateFromChild(child As CurveLegend.CurveLegendAccessibleObject, _
navdir As AccessibleNavigation) As AccessibleObject
Select Case navdir
Case AccessibleNavigation.Down, AccessibleNavigation.Next
Return GetChild(child.ID + 1)
Case AccessibleNavigation.Up, AccessibleNavigation.Previous
Return GetChild(child.ID - 1)
End Select
Return Nothing
End Function
' Helper function that is used by the CurveLegend's accessibility object
' to select a specific CurveLegend control. Specifically, this function is used
' in the CurveLegend.CurveLegendAccessibleObject.Select function.
Friend Sub SelectChild(child As CurveLegend.CurveLegendAccessibleObject, selection As AccessibleSelection)
Dim childID As Integer = child.ID
' Determine which selection action should occur, based on the
' AccessibleSelection value.
If (selection And AccessibleSelection.TakeSelection) <> 0 Then
Dim i As Integer
For i = 0 To chartControl.Legends.Length - 1
If i = childID Then
chartControl.Legends(i).Selected = True
Else
chartControl.Legends(i).Selected = False
End If
Next i
' AccessibleSelection.AddSelection means that the CurveLegend will be selected.
If (selection And AccessibleSelection.AddSelection) <> 0 Then
chartControl.Legends(childID).Selected = True
End If
' AccessibleSelection.AddSelection means that the CurveLegend will be unselected.
If (selection And AccessibleSelection.RemoveSelection) <> 0 Then
chartControl.Legends(childID).Selected = False
End If
End If
End Sub 'SelectChild
End Class 'ChartControlAccessibleObject
// Inner class ChartControlAccessibleObject represents accessible information associated with the ChartControl.
// The ChartControlAccessibleObject is returned in the ChartControl.CreateAccessibilityInstance override.
public class ChartControlAccessibleObject : ControlAccessibleObject
{
ChartControl chartControl;
public ChartControlAccessibleObject(ChartControl ctrl) : base(ctrl)
{
chartControl = ctrl;
}
// Gets the role for the Chart. This is used by accessibility programs.
public override AccessibleRole Role
{
get {
return AccessibleRole.Chart;
}
}
// Gets the state for the Chart. This is used by accessibility programs.
public override AccessibleStates State
{
get {
return AccessibleStates.ReadOnly;
}
}
// The CurveLegend objects are "child" controls in terms of accessibility so
// return the number of ChartLengend objects.
public override int GetChildCount()
{
return chartControl.Legends.Length;
}
// Gets the Accessibility object of the child CurveLegend idetified by index.
public override AccessibleObject GetChild(int index)
{
if (index >= 0 && index < chartControl.Legends.Length) {
return chartControl.Legends[index].AccessibilityObject;
}
return null;
}
// Helper function that is used by the CurveLegend's accessibility object
// to navigate between sibiling controls. Specifically, this function is used in
// the CurveLegend.CurveLegendAccessibleObject.Navigate function.
internal AccessibleObject NavigateFromChild(CurveLegend.CurveLegendAccessibleObject child,
AccessibleNavigation navdir)
{
switch(navdir) {
case AccessibleNavigation.Down:
case AccessibleNavigation.Next:
return GetChild(child.ID + 1);
case AccessibleNavigation.Up:
case AccessibleNavigation.Previous:
return GetChild(child.ID - 1);
}
return null;
}
// Helper function that is used by the CurveLegend's accessibility object
// to select a specific CurveLegend control. Specifically, this function is used
// in the CurveLegend.CurveLegendAccessibleObject.Select function.
internal void SelectChild(CurveLegend.CurveLegendAccessibleObject child, AccessibleSelection selection)
{
int childID = child.ID;
// Determine which selection action should occur, based on the
// AccessibleSelection value.
if ((selection & AccessibleSelection.TakeSelection) != 0) {
for(int i = 0; i < chartControl.Legends.Length; i++) {
if (i == childID) {
chartControl.Legends[i].Selected = true;
} else {
chartControl.Legends[i].Selected = false;
}
}
// AccessibleSelection.AddSelection means that the CurveLegend will be selected.
if ((selection & AccessibleSelection.AddSelection) != 0) {
chartControl.Legends[childID].Selected = true;
}
// AccessibleSelection.AddSelection means that the CurveLegend will be unselected.
if ((selection & AccessibleSelection.RemoveSelection) != 0) {
chartControl.Legends[childID].Selected = false;
}
}
}
}
// Inner class ChartControlAccessibleObject represents accessible information associated with the ChartControl.
// The ChartControlAccessibleObject is returned in the ChartControl::CreateAccessibilityInstance .
ref class ChartControlAccessibleObject: public ControlAccessibleObject
{
private:
ChartControl^ chartControl;
public:
ChartControlAccessibleObject( ChartControl^ ctrl )
: ControlAccessibleObject( ctrl )
{
chartControl = ctrl;
}
property System::Windows::Forms::AccessibleRole Role
{
// Gets the role for the Chart. This is used by accessibility programs.
virtual System::Windows::Forms::AccessibleRole get() override
{
return ::AccessibleRole::Chart;
}
}
property AccessibleStates State
{
// Gets the state for the Chart. This is used by accessibility programs.
virtual AccessibleStates get() override
{
return AccessibleStates::ReadOnly;
}
}
// The CurveLegend objects are "child" controls in terms of accessibility so
// return the number of ChartLengend objects.
virtual int GetChildCount() override
{
return chartControl->Legends->Length;
}
// Gets the Accessibility object of the child CurveLegend idetified by index.
virtual AccessibleObject^ GetChild( int index ) override
{
if ( index >= 0 && index < chartControl->Legends->Length )
{
return chartControl->Legends[ index ]->AccessibilityObject;
}
return nullptr;
}
internal:
// Helper function that is used by the CurveLegend's accessibility object
// to navigate between sibiling controls. Specifically, this function is used in
// the CurveLegend::CurveLegendAccessibleObject.Navigate function.
AccessibleObject^ NavigateFromChild( CurveLegend::CurveLegendAccessibleObject^ child, AccessibleNavigation navdir )
{
switch ( navdir )
{
case AccessibleNavigation::Down:
case AccessibleNavigation::Next:
return GetChild( child->ID + 1 );
case AccessibleNavigation::Up:
case AccessibleNavigation::Previous:
return GetChild( child->ID - 1 );
}
return nullptr;
}
// Helper function that is used by the CurveLegend's accessibility object
// to select a specific CurveLegend control. Specifically, this function is used
// in the CurveLegend::CurveLegendAccessibleObject.Select function.
void SelectChild( CurveLegend::CurveLegendAccessibleObject^ child, AccessibleSelection selection )
{
int childID = child->ID;
// Determine which selection action should occur, based on the
// AccessibleSelection value.
if ( (selection & AccessibleSelection::TakeSelection) != (AccessibleSelection)0 )
{
for ( int i = 0; i < chartControl->Legends->Length; i++ )
{
if ( i == childID )
{
chartControl->Legends[ i ]->Selected = true;
}
else
{
chartControl->Legends[ i ]->Selected = false;
}
}
// AccessibleSelection->AddSelection means that the CurveLegend will be selected.
if ( (selection & AccessibleSelection::AddSelection) != (AccessibleSelection)0 )
{
chartControl->Legends[ childID ]->Selected = true;
}
// AccessibleSelection->AddSelection means that the CurveLegend will be unselected.
if ( (selection & AccessibleSelection::RemoveSelection) != (AccessibleSelection)0 )
{
chartControl->Legends[ childID ]->Selected = false;
}
}
}
};
// class ChartControlAccessibleObject
// Inner class ChartControlAccessibleObject represents accessible
// information associated with the ChartControl.
// The ChartControlAccessibleObject is returned in the
// ChartControl.CreateAccessibilityInstance override.
public static class ChartControlAccessibleObject
extends ControlAccessibleObject
{
private ChartControl chartControl;
public ChartControlAccessibleObject(ChartControl ctrl)
{
super(ctrl);
chartControl = ctrl;
} //ChartControlAccessibleObject
// Gets the role for the Chart. This is used by accessibility programs.
/** @property
*/
public AccessibleRole get_Role()
{
return AccessibleRole.Chart;
} //get_Role
// Gets the state for the Chart. This is used by accessibility programs.
/** @property
*/
public AccessibleStates get_State()
{
return AccessibleStates.ReadOnly;
} //get_State
// The CurveLegend objects are "child" controls in terms of
// accessibility so return the number of ChartLengend objects.
public int GetChildCount()
{
return chartControl.get_Legends().get_Length();
} //GetChildCount
// Gets the Accessibility object of the child CurveLegend
// idetified by index.
public AccessibleObject GetChild(int index)
{
if (index >= 0 && index < chartControl.get_Legends().get_Length()) {
return chartControl.get_Legends()[index].
get_AccessibilityObject();
}
return null;
} //GetChild
// Helper function that is used by the CurveLegend's accessibility
// object to navigate between sibiling controls.
// Specifically, this function is used in
// the CurveLegend.CurveLegendAccessibleObject.Navigate function.
AccessibleObject NavigateFromChild(
CurveLegend.CurveLegendAccessibleObject child,
AccessibleNavigation navDir)
{
if (navDir.Equals(AccessibleNavigation.Down)
|| navDir.Equals(AccessibleNavigation.Next)) {
return GetChild(child.get_ID() + 1);
}
else {
if (navDir.Equals(AccessibleNavigation.Up)
|| navDir.Equals(AccessibleNavigation.Previous)) {
return GetChild(child.get_ID() - 1);
}
}
return null;
} //NavigateFromChild
// Helper function that is used by the CurveLegend's accessibility
// object to select a specific CurveLegend control.
// Specifically, this function is used
// in the CurveLegend.CurveLegendAccessibleObject.Select function.
public void SelectChild(CurveLegend.CurveLegendAccessibleObject child,
AccessibleSelection selection)
{
int childID = child.get_ID();
// Determine which selection action should occur, based on the
// AccessibleSelection value.
if (Convert.ToInt32(selection & AccessibleSelection.TakeSelection)
!= 0) {
for (int i = 0; i < chartControl.get_Legends().get_Length();
i++) {
if (i == childID) {
((CurveLegend)chartControl.get_Legends().get_Item(i)).
set_Selected(true);
}
else {
((CurveLegend)chartControl.get_Legends().get_Item(i)).
set_Selected(false);
}
}
// AccessibleSelection.AddSelection means that the CurveLegend
// will be selected.
if (Convert.ToInt32(selection & AccessibleSelection.AddSelection)
!= 0) {
((CurveLegend)chartControl.get_Legends().get_Item(childID)).
set_Selected(true);
}
// AccessibleSelection.AddSelection means that the CurveLegend
// will be unselected.
if (Convert.ToInt32(selection &
AccessibleSelection.RemoveSelection) != 0) {
((CurveLegend)chartControl.get_Legends().get_Item(childID)).
set_Selected(false);
}
}
} //SelectChild
} //ChartControlAccessibleObject
平台
Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Mobile for Smartphone、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition
.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。
版本信息
.NET Framework
受以下版本支持：2.0、1.1、1.0
请参见
参考
AccessibleObject 类
AccessibleObject 成员
System.Windows.Forms 命名空间