IAccessible::get_accFocus method (oleacc.h)

Makale
10/13/2021

The IAccessible::get_accFocus method retrieves the object that has the keyboard focus. All objects that may receive the keyboard focus must support this property.

Syntax

HRESULT get_accFocus(
  [out, retval] VARIANT *pvarChild
);

Parameters

[out, retval] pvarChild

Type: VARIANT*

Address of a VARIANT structure that receives information about the object that has the focus. The following table describes the information returned in pvarID.

Value	Meaning
VT_EMPTY	None. Neither this object nor any of its children has the keyboard focus.
VT_I4	lVal is CHILDID_SELF. The object itself has the keyboard focus.
VT_I4	lVal contains the child ID of the child element that has the keyboard focus.
VT_DISPATCH	pdispVal member is the address of the IDispatch interface for the child object that has the keyboard focus.

Return value

Type: HRESULT

If successful, returns S_OK.

If not successful, returns one of the values in the table that follows, or another standard COM error code. Servers return these values, but clients must always check output parameters to ensure that they contain valid values. For more information, see Checking IAccessible Return Values.

Error	Description
S_FALSE	The object is a window but not the foreground window.
DISP_E_MEMBERNOTFOUND	The object does not support this property.

Remarks

The concept of keyboard focus is related to that of an active window. An active window is the foreground window on which the user works. The object with the keyboard focus is either the active window or a child object of the active window.

Only one object or item within a container has the focus at any one time. The object with the keyboard focus is not always the selected object. For more information about the difference between selection and focus, see Selection and Focus Properties and Methods.

This method returns either an IDispatch interface pointer or a child ID for the pvarID. For more information about how to use the IDispatch interface pointer or child ID, see How Child IDs Are Used in Parameters.

As with other IAccessible methods and functions, clients might receive errors for IAccessible interface pointers because of a user action. For more information, see Receiving Errors for IAccessible Interface Pointers.

Server Example

The following example code shows a possible implementation of this method for a custom single-selection list box. If the control does not have the focus, VT_EMPTY is returned in the variant by the standard accessible object for the HWND. If the control does have the focus, and an item is selected, the child ID of that item is returned; if there is no selection, CHILDID_SELF is returned.


// m_pControl is the control object that is served by this implementation. 
// m_pStdAccessibleObject is the object returned by CreateStdAccessibleObject. 

HRESULT STDMETHODCALLTYPE AccServer::get_accFocus(VARIANT *pvarChild)
{
    FAIL_IF_NO_CONTROL;  // Macro that checks for existence of control. 

    HRESULT hr = m_pStdAccessibleObject->get_accFocus(pvarChild);  
    if (pvarChild->vt != VT_I4)
    {
        return hr;
    }
    else
    {
        int index = m_pControl->GetSelectedIndex();
        if (index <0)
        {
            pvarChild->lVal = CHILDID_SELF;
        }
        else
        {
            // Convert to 1-based index for child ID. 
            pvarChild->lVal = index + 1;
        }
    }
    return S_OK;
};

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows Server 2003 [desktop apps only]
Target Platform	Windows
Header	oleacc.h
Library	Oleacc.lib
DLL	Oleacc.dll
Redistributable	Active Accessibility 1.3 RDK on Windows NT 4.0 with SP6 and later and Windows 95

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