AccessibleObject.GetChild-Methode
Ruft das zugreifbare untergeordnete Element entsprechend dem angegebenen Index ab.
Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in system.windows.forms.dll)
Syntax
'Declaration
Public Overridable Function GetChild ( _
index As Integer _
) As AccessibleObject
'Usage
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
Parameter
- index
Der nullbasierte Index des zugreifbaren untergeordneten Elements.
Rückgabewert
Ein AccessibleObject, das das zugreifbare untergeordnete Element darstellt, das dem angegebenen Index entspricht.
Hinweise
Hinweise für Erben Diese Eigenschaft muss von allen zugreifbaren Objekten unterstützt werden. Wenn die Methode nicht überschrieben wird, gibt sie NULL (Nothing in Visual Basic) zurück. Überschreiben Sie diese Methode, wenn ein zugreifbares Objekt zugreifbare untergeordnete Elemente bereitstellen muss, die benutzerdefiniert sind. Wenn der Index ungültig ist, gibt diese Methode NULL (Nothing in Visual Basic) zurück. Wenn Sie diese Methode überschreiben, müssen Sie GetChildCount ebenfalls überschreiben.
Beispiel
Das folgende Beispiel veranschaulicht die Erstellung eines Chart-Steuerelements mit Eingabehilfenunterstützung unter Verwendung der AccessibleObject-Klasse und der Control.ControlAccessibleObject-Klasse zum Verfügbarmachen von Eingabehilfeninformationen. Das Steuerelement zeichnet zwei Kurven mit einer Legende. Die von ControlAccessibleObject abgeleitete ChartControlAccessibleObject-Klasse wird in der CreateAccessibilityInstance-Methode verwendet, um benutzerdefinierte Eingabehilfeninformationen für das Chart-Steuerelement bereitzustellen. Da die Diagrammlegende kein tatsächlich Control-basiertes Steuerelement darstellt, sondern vom Chart-Steuerelement gezeichnet wird, weist es keine integrierten Eingabehilfeninformationen auf. Aus diesem Grund überschreibt die ChartControlAccessibleObject-Klasse die GetChild-Methode, um das CurveLegendAccessibleObject zurückzugeben, das die Eingabehilfeninformationen für alle Teile der Legende darstellt. Wenn eine Anwendung mit Eingabehilfenunterstützung dieses Steuerelement verwendet, kann das Steuerelement die erforderlichen Eingabehilfeninformationen bereitstellen.
Dieser Codeauszug veranschaulicht das Überschreiben der GetChild-Methode. Das vollständige Codebeispiel finden Sie in der Übersicht zur AccessibleObject-Klasse.
' 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
Plattformen
Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile für Pocket PC, Windows Mobile für Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
.NET Framework unterstützt nicht alle Versionen sämtlicher Plattformen. Eine Liste der unterstützten Versionen finden Sie unter Systemanforderungen.
Versionsinformationen
.NET Framework
Unterstützt in: 2.0, 1.1, 1.0
Siehe auch
Referenz
AccessibleObject-Klasse
AccessibleObject-Member
System.Windows.Forms-Namespace