RELEASE OBJECT statement

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 ]

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.

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.

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.