IAccessible::get_accRole

發行項
03/28/2008

The IAccessible::get_accRole method retrieves information that describes the role of the specified object. All objects support this property.

HRESULT get_accRole(
VARIANTvarID,VARIANT* pvarRole);

Parameters

varID
[in] Specifies whether the role information retrieved is that of the object or of one of the object's child elements. This parameter is either CHILDID_SELF (to obtain information about the object) or a child ID (to obtain information about the object's child element). For more information about initializing the VARIANT structure, see How Child IDs Are Used in Parameters.
pvarRole
[out, retval] Address of a VARIANT structure that receives an object role constant. The variant member must be VT_I4, and the IVal member contains an object role constant.

Return Values

If successful, returns S_OK.

If not successful, returns the following value or another standard COM error code. Although servers return these values, clients must always check output parameters to ensure that they contain valid values. For more information, see Checking IAccessible Return Values.

Error	Description
E_INVALIDARG	An argument is invalid.

Remarks

Clients call GetRoleText to retrieve a localized string that describes the object's role.

Note to server developers You must use the predefined role constants.

Server Example

The following example code is a possible implementation of this method for a custom list box that maintains its own list items.

HRESULT STDMETHODCALLTYPE AccServer::get_accRole( 
    VARIANT varChild,
    VARIANT *pvarRole)
{
    if (varChild.vt != VT_I4)
    {
        pvarRole->vt = VT_EMPTY;
        return E_INVALIDARG;
    }

    pvarRole->vt = VT_I4;

    if (varChild.lVal == CHILDID_SELF)
    {
        pvarRole->lVal = ROLE_SYSTEM_LIST;
    }
    else
    {
        pvarRole->lVal = ROLE_SYSTEM_LISTITEM;
    }
    return S_OK;
};

Client Example

The following example function displays the role of an accessible object or child element.

HRESULT PrintRole(IAccessible* pAcc, long childId)
{
    DWORD roleId;
    if (pAcc == NULL)
    {
        return E_INVALIDARG;    
    }
    VARIANT varChild;
    varChild.vt = VT_I4;
    varChild.lVal = childId;
    VARIANT varResult;
    HRESULT hr = pAcc->get_accRole(varChild, &varResult;);
    if ((hr == S_OK) && (varResult.vt == VT_I4))
    {
        roleId = varResult.lVal;
        UINT   roleLength;
        LPTSTR lpszRoleString;

        // Get the length of the string.
        roleLength = GetRoleText(roleId, NULL, 0);

        // Allocate memory for the string. Add one character to
        // the length you got in the previous call to make room
        // for the null character.
        lpszRoleString = (LPTSTR)malloc((roleLength+1) * sizeof(TCHAR));
        if (lpszRoleString != NULL)
        {
            // Get the string.
            GetRoleText(roleId, lpszRoleString, roleLength + 1);
#ifdef UNICODE
            printf("Role: %S\n", lpszRoleString);
#else
            printf(("Role: %s\n", lpszRoleString);
#endif
            // Free the allocated memory
            free(lpszRoleString);
        }
        else 
        {
            return E_OUTOFMEMORY;
        }
    }
    return S_OK;
}

Requirements

**  Windows NT/2000/XP/Server 2003:** Included in Windows 2000 and later.
**  Windows 95/98/Me:** Included in Windows 98 and later.
**  Redistributable:** Requires Active Accessibility 1.3 RDK on Windows NT 4.0 SP6 and Windows 95.
**  Header:** Declared in Oleacc.h.
**  Library:** Use Oleacc.lib.

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