Releases the specified COM object (Automation
object or ActiveX control) and removes all internal structures associated
with the handle to the object.
Syntax
RELEASE OBJECT COM-hdl-var[ NO-ERROR ]
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-
COM-hdl-var
- A COM-HANDLE variable that references a valid COM object.
- NO-ERROR
- Suppresses ABL errors or error messages that would otherwise
occur and diverts them to the ERROR-STATUS system handle. If an error occurs, the action of the statement
is not done and execution continues with the next statement. If
the statement fails, any persistent side-effects of the statement
are backed out. If the statement includes an expression that contains
other executable elements, like methods, the work performed by these
elements may or may not be done, depending on the order the AVM
resolves the expression elements and the occurrence of the error.
To
check for errors after a statement that uses the NO-ERROR option:
- Check the ERROR-STATUS:ERROR attribute to see if the AVM raised
the ERROR condition.
- Check if the ERROR-STATUS:NUM-MESSAGES attribute is greater than
zero to see if the AVM generated error messages. ABL handle methods
used in a block without a CATCH end block treat errors as
warnings and do not raise ERROR, do not set the ERROR-STATUS:ERROR
attribute, but do add messages to the ERROR-STATUS system handle.
Therefore, this test is the better test for code using handle methods
without CATCH end blocks. ABL handle methods used in a block with a
CATCH end block raise ERROR and add messages to the error object
generated by the AVM. In this case, the AVM does not update the
ERROR-STATUS system handle.
- Use ERROR-STATUS:GET-MESSAGE( message-num )
to retrieve a particular message, where message-num is
1 for the first message.
If the statement does not include
the NO-ERROR option, you can use a CATCH end block to handle errors
raised by the statement.
Some other important usage notes
on the NO-ERROR option:
- NO-ERROR does not suppress errors
that raise the STOP or QUIT condition.
- A CATCH statement, which introduces a CATCH end block, is analogous
to a NO-ERROR option in that it also suppresses errors, but it does so
for an entire block of code. It is different in that the error messages
are contained in a class-based error object (generated by the AVM
or explicitly thrown), as opposed to the ERROR-STATUS system handle.
Also, if errors raised in the block are not handled by a compatible
CATCH block, ON ERROR phrase, or UNDO statement, then the error
is not suppressed, but handled with the default error processing
for that block type.
- When a statement contains the NO-ERROR option and resides in
a block with a CATCH end block, the NO-ERROR option takes precedence over
the CATCH block. That is, an error raised on the statement with
the NO-ERROR option will not be handled by a compatible CATCH end block.
The error is redirected to the ERROR-STATUS system handle as normal.
- If an error object is thrown to a statement that includes the NO-ERROR
option, then the information and messages in the error object will
be used to set the ERROR-STATUS system handle. This interoperability
feature is important for those integrating code that uses the traditional
NO-ERROR technique with the newer, structured error handling that
features error objects and CATCH end blocks.
Example
This
procedure fragment shows a control named hc_CmdButton being loaded
into a control-frame and the handle to the control (controlHdl)
being obtained using the control name (hc_CmdButton) property. Later,
it releases the control and deletes the parent control-frame widget
(CFWidHdl).
DEFINE VARIABLE CFWidHdl AS HANDLE NO-UNDO.
DEFINE VARIABLE CFComHdl AS COM-HANDLE NO-UNDO.
DEFINE VARIABLE controlHdl AS COM-HANDLE NO-UNDO.
/* Create frame foo ... */
CREATE CONTROL-FRAME CFWidHdl ASSIGN
FRAME = FRAME foo:HANDLE
NAME = "ctlFrame1".
CFComHdl = CFWidHdl:COM-HANDLE.
CFComHdl:LoadControls(hc_CmdButton.wrx, "hc_CmdButton").
controlHdl = CFComHdl:hc_CmdButton.
controlHdl:BgColor = RGB-VALUE(0,128,0).
/* Do some more stuff ... WAIT-FOR ... */
RELEASE OBJECT controlHdl. /* NOTE: Not really necessary */
DELETE WIDGET CFWidHdl.
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For an example of the RELEASE OBJECT statement
applied to Automation objects, see the CREATE automation object statement entry.
Notes
- After
this statement completes, any other component handles that reference
the object are invalid. If you attempt to reference the object using
one of these handles, the AVM returns an invalid handle error. It
is also possible for a newly instantiated COM object to get the
same handle as one that has been released. The AVM does not detect
that this occurs. In this case, the "old" handle is valid, but it
references a different control. Thus, it is a good practice to set
any COM-HANDLE variables that reference a released COM object to
the Unknown value (?).
- The released COM object remains active as long as any other
COM object has a valid reference to it. In the case of an ActiveX
control, the parent control-frame is a COM object that references
the control. All other component handle references you establish
in the ABL session represent a second reference to the COM object.
Thus, when you release one of these component handles, the released
COM object remains active as long as the parent control-frame COM
object is still active. To release the parent control-frame COM
object and complete the release of the ActiveX control, you must
follow any release of the ActiveX control by a delete of the parent
control-frame widget.
- When you delete a control-frame widget, the AVM releases all
associated ActiveX controls automatically, whether or not you release
them individually.
- When the session ends, the AVM automatically releases any active COM
objects you have not released individually.