Both the AddItem and AddListItem methods add items to combo boxes or listboxes. This article highlights their functionality and the differencesbetween the two methods. In particular, this article demonstrates why theAddListitem method might be a better way to populate a multiple-columncombo box.
The Additem and AddlistItem methods add items to a list and accept twooptional parameters. The differences between the two methods are mirroredin the differences between their first parameter; AddItem acceptsnListIndex as its first parameter, and AddListItem accepts nListItemIdas its first parameter.
There are two ways to identify an item in a list:
- Its relative position, which represents the order in which the items are displayed in the list. If an item is added to the list, the relative position of other items might change. This is similar to the index order of a table. The integer that holds this value is referred as nIndex.
- Its absolute position, which represents the order in which the item is added to the list. This value is not dependent on the way items are displayed in the list, and it does not change as the number of items in the list are modified. This concept is similar to the RECNO() function, which is used to identify records in a table. The integer that holds this value is referred as nItemId.
These two numbers can be identical, but they are different when the list issorted, or when items are added or removed from the list.
The Additem method inserts an item based on its relative position in thelist. The syntax is:
Control.AddItem(cItem [, nIndex] [, nColumn])
The AddListItem method allows you to create a unique id for the item, anduses nItemId. If the item already exists, the prompt is replaced. Thesyntax is:
Control.AddListItem(cItem [, nItemID] [, nColumn])
The following example illustrates how to use the Additem and AddListItemmethods. To run the example, copy and paste the code in a program file.
Omyform=CREATE('myform')Omyform.Show()READ EVENTSDEFINE Class myform AS Form ADD OBJECT list1 AS mylist ADD OBJECT list2 AS mylist2 ADD OBJECT cmd1 AS cmdquitENDDEFINEDEFINE Class cmdquit AS CommandButton Top=105 Left = 55 Caption="Quit" PROCEDURE Click CLEAR EVENTS RELEASE Thisform ENDPROCENDDEFINEDEFINE Class mylist AS ListBox && Defines a list filled with Additem Top = 3 Left=5 Width=90 Height=90 RowSourceType=0 PROCEDURE Init This.AddItem('Apples',1) This.AddItem('Oranges',2) This.AddItem('Lemons',2) && Element inserted before 'Oranges' ENDPROCENDDEFINEDEFINE Class mylist2 AS ListBox &&Defines a list filled with AddListitem Top = 3 Left=100 Width=90 Height=90 RowSourceType=0 PROCEDURE Init This.AddListItem('Apples',1) This.AddListItem('Oranges',2) This.AddListItem('Lemons',2) && Prompt overwrites 'Oranges' ENDPROCENDDEFINE
Multiple-Column List Boxes
The AddItem method might not yield expected results when it is used topopulate a multiple-column list box. The following step-by-step exampleillustrates how the elements of a multiple-column list box are displayedwhen the AddItem method is used.
- Create a form.
- Place a list box on the form.
- Change the following properties of the list box:
ColumnCount : 2 ColumnWidths: 80,80
- Save the form as TestForm, and run it.
- In the Command window, type:
TestForm.List1.AddItem("One",1,1) TestForm.List1.AddItem("Two",1,2) TestForm.List1.AddItem("Three",2,1) TestForm.List1.AddItem("Four",2,2)
The resulting list looks as follows:
--------------------- | | Two | | | Four | | Three | | | One | | ---------------------
This occurs because the AddItem inserts each item at the relative positionspecified by the nIndex integer.
Use the ListItemId to populate a multiple-column combo box and add items onthe same row. By using the example above and replacing AddItem withAddListItem, the list looks like this:
------------------------ | One | Two | | Three | Four | ------------------------
For more information about the AddItem and AddListItem methods, search for"AddItem" or "AddListItem" in the Visual FoxPro Help file.