DELETE WIDGET-POOL statement

Deletes a defined widget pool.

Syntax

DELETE WIDGET-POOL [ pool-name ][ NO-ERROR ]

pool-name

The name of a defined dynamic widget pool. If you omit pool-name, the statement deletes the unnamed pool most recently created in the current or a calling procedure or class-based method.

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

The following example creates a named widget pool and lets you add buttons to it. When you choose Delete Buttons, the widget pool is deleted. (Therefore all the buttons in the pool are also deleted.) Similarly, when you choose Quit to exit the procedure the widget pool is also deleted. Because the pool is persistent, it remains allocated for the rest of your session if you do not delete it.

r-widpl.p

DEFINE VARIABLE wh AS HANDLE NO-UNDO.

DEFINE BUTTON b_create LABEL "Create Button".
DEFINE BUTTON b_del    LABEL "Delete Buttons".
DEFINE BUTTON b_quit   LABEL "Quit"
  TRIGGERS:
    ON CHOOSE DO:
      IF VALID-HANDLE(wh) THEN
        DELETE WIDGET-POOL "new-buttons".
      QUIT.
    END.
  END.
  
DEFINE FRAME butt-frame
  b_create b_del b_quit
  WITH ROW SCREEN-LINES - 2.

DEFINE FRAME new-buttons
  WITH SIZE 76 BY 11 CENTERED ROW 2 TITLE "New Buttons".

ON CHOOSE OF b_create IN FRAME butt-frame DO:
  STATUS INPUT "Press RETURN to select a new button".
  IF wh = ? OR NOT VALID-HANDLE(wh) THEN
    CREATE WIDGET-POOL "new-buttons" PERSISTENT.
  CREATE BUTTON wh IN WIDGET-POOL "new-buttons" ASSIGN
    FRAME     = FRAME new-buttons:HANDLE
    ROW       = RANDOM(2, 9)
    COLUMN    = RANDOM(2, 58)
    LABEL     = "BUTTON " + STRING(etime)
    SENSITIVE = TRUE
    VISIBLE   = TRUE
    MOVABLE   = TRUE
    TRIGGERS:
      ON CHOOSE PERSISTENT RUN dispmsg.
    END.
END.

ON CHOOSE OF b_del IN FRAME butt-frame DO:
  IF VALID-HANDLE(wh) THEN
    DELETE WIDGET-POOL "new-buttons".
  STATUS INPUT.
END.

ENABLE b_create b_del b_quit WITH FRAME butt-frame.
WAIT-FOR CHOOSE OF b_quit IN FRAME butt-frame.

PROCEDURE dispmsg:
  MESSAGE "You chose button " SELF:LABEL.
END PROCEDURE.

Notes

• When you delete a widget pool, all widgets in that pool are automatically deleted.
• If you do not delete a non-persistent widget pool, it is deleted when the procedure or method that created it ends. If you do not delete a persistent widget pool, it is deleted when the session ends.
• All named widget pools are globally scoped. While a named widget pool is allocated, any procedure or method within the same process can access that widget pool. If you try to delete a named widget pool that does not exist, the AVM raises the ERROR condition.

See also

CREATE WIDGET-POOL statement, DELETE WIDGET statement