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AccessibleObject.Role Property

Gets the role of this accessible object.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in system.windows.forms.dll)

public virtual AccessibleRole Role { get; }
/** @property */
public AccessibleRole get_Role ()

public function get Role () : AccessibleRole

Not applicable.

Property Value

One of the AccessibleRole values, or AccessibleRole.None if no role has been specified.

The role of the object helps describe the function of the object.

Notes to Inheritors: All objects should support this property.

The following example demonstrates the creation of an accessibility-aware chart control, using the AccessibleObject and Control.ControlAccessibleObject classes to expose accessible information. The control plots two curves along with a legend. The ChartControlAccessibleObject class, which derives from ControlAccessibleObject, is used in the CreateAccessibilityInstance method to provide custom accessible information for the chart control. Since the chart legend is not an actual Control -based control, but instead is drawn by the chart control, it does not have any built-in accessible information. Because of this, the ChartControlAccessibleObject class overrides the GetChild method to return the CurveLegendAccessibleObject that represents accessible information for each part of the legend. When an accessible-aware application uses this control, the control can provide the necessary accessible information.

This code excerpt demonstrates overriding the Role property. See the AccessibleObject class overview for the complete code example.

// 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 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

Windows 98, Windows Server 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

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

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