CLEAR LIST
CLEAR LIST ( list {; *} )
| Parameter | Type | Description | |
|---|---|---|---|
| list | Integer | → | List reference number |
| * | Operator | → | If specified, clear sublists from memory, if any. If omitted, sublists (if any) are not cleared. |
This command is not thread-safe, it cannot be used in preemptive code.
Description
The CLEAR LIST command deletes the hierarchical list whose list reference number you pass in list.
Usually you will pass the optional * parameter, so all the sublists, if any, attached to items or subitems of the list will be deleted as well.
You do not need to clear a list attached to a form object via the Property List window. 4D loads and clears the list for you. On the other hand, each time you load, copy, extract from a BLOB, or create a list programmatically, call CLEAR LIST when you are through with the list.
To clear a sublist attached to an item (on any level) of another list currently displayed in a form, proceed as follows:
- Call GET LIST ITEM on the parent item to get the list reference of the sublist.
- Call SET LIST ITEM on the parent item to detach the sublist from the list item before clearing it.
- Call CLEAR LIST to clear the sublist whose reference number you obtained with GET LIST ITEM.
Example 1
Within a clean-up routine that clears all objects and data that you no longer need (i.e., when a window is closed and a form unloaded), you may end up clearing a hierarchical list that may have already been cleared, depending on the user actions within the form. Use Is a list to clear the list only if necessary:
// Extract of clean-up routine
If(Is a list(hlList))
CLEAR LIST(hlList;*)
End if
Example 2
See example for the Load list command.
Example 3
See example for the BLOB to list command.