CREATE WIDGET-POOL statement

Creates a named or unnamed widget pool in which to contain most dynamic widgets and other handle-based objects created during an ABL session.

Syntax

CREATE WIDGET-POOL
  [ pool-name [ PERSISTENT ] ]
  [ NO-ERROR ]

pool-name

A character-string expression that specifies the name for a named widget pool you are creating. Widget pool names are not case sensitive.

If you omit this option, an unnamed widget pool is created and scoped to the procedure or class-based method. That is, a routine-scoped unnamed widget pool and its contents remain in effect as long as the procedure or method is on the call stack, and the pool and its contents are automatically deleted when the procedure or method is removed from the call stack.

PERSISTENT

Specifies that the named widget pool is persistent. This means that the pool and any widgets in it remain allocated after the current procedure or method terminates. If you do not specify this option, the pool and its contents are automatically deleted when procedure or method execution ends.

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 lets you create a series of dynamic buttons. All the buttons are created within a named widget pool. Because the widget pool is created within a trigger, it is defined as persistent so that it remains allocated after the trigger ends. You can at any time choose to delete the entire widget pool and start over.

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
    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.

DO ON ENDKEY UNDO, LEAVE:
  WAIT-FOR CHOOSE OF b_quit IN FRAME butt-frame.
END.

IF VALID-HANDLE(wh) THEN 
  DELETE WIDGET-POOL "new-buttons".

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

Notes

• The AVM automatically creates a persistent unnamed widget pool (session widget pool) at the start of each session. Most applications use only this session widget pool.
• In general, unnamed widget pools cannot persist beyond the scope of the procedure or method in which they are created, except the session widget pool, which is created by the AVM.
• If you create an unnamed widget pool in the main block of a persistent procedure or you instantiate a class where the USE-WIDGET-POOL option is defined somewhere in its hierarchy, the AVM creates an object-persistent unnamed widget pool that persists for the lifetime of the persistent procedure or class-based object, respectively. This object-persistent widget pool then becomes the default widget pool for any internal procedure of the persistent procedure or any method of the instantiated class that is invoked from outside the respective persistent procedure or instantiated class. However, any routine-scoped unnamed widget pool created by these internal procedures or methods supersedes this object-persistent widget pool. For more information on the USE-WIDGET-POOL option, see the CLASS statement reference entry.
• When you create an unnamed widget pool, it automatically becomes the default widget pool. Each subsequent dynamically created widget is placed in this unnamed pool unless you specifically assign it to another pool. This unnamed pool remains the default widget pool until it is deleted or you create another unnamed widget pool. Thus, if you create no unnamed widget pools, all dynamically created widgets go into the session widget pool, unless assigned to another pool. If you create any additional unnamed widget pools, either object-persistent or routine-scoped, the most locally scoped and recently created unnamed widget pool becomes the default widget pool for all subsequently created dynamic widgets.
• Persistent widget pools remain allocated until they are explicitly deleted (with the DELETE WIDGET-POOL statement) or until the end of the ABL session that created them.
• All named widget pools are globally scoped. While a named widget pool is allocated, any procedure within the same process can access that widget pool. The name of a widget pool must be unique among all widget pools for the process. If you try to create a widget pool with the same name as an existing pool, the AVM raises the ERROR condition.
• If a recursive procedure or method creates an unnamed widget pool, each iteration of that procedure or method creates a separate pool. If a recursive routine creates a named widget pool, you must ensure that only one iteration creates the pool (where all iterations can share it) or use a different name in each iteration (where each creates and uses its own pool).
• You might want to create a new, unnamed widget pool just before invoking a new procedure or method and then delete that pool when the procedure or method returns. This ensures that any dynamic widgets created by that procedure or method in the default pool are deleted immediately. For example:

  CREATE WIDGET-POOL. RUN xyz.p. DELETE WIDGET-POOL.

  Similarly, you might want to store all dynamic widgets for a subsystem within a specific named pool. For example:

  CREATE WIDGET-POOL "oe-pool". RUN ord-ent.p DELETE WIDGET-POOL "oe-pool".

  In this example, the procedure ord-ent.p must reference the oe-pool for each dynamic widget it creates.

See also

CLASS statement, CREATE widget statement, DELETE WIDGET-POOL statement