HOWTO: Populate a Form's List Box Object from an Array
ID: Q129329
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The information in this article applies to:
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Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b, 5.0, 6.0
SUMMARY
This article shows how to populate a ListBox object from an array.
MORE INFORMATION
In Visual FoxPro, in addition to the usual single-column list, you can now
have multiple-column lists. Additionally, the ListBox object also supports
the multiple-select and mover capabilities.
The ListBox object has several properties that control the displayed
output. Some of these properties are covered in this article. For more
information, please see Chapter 11 of the Developer's Guide or the "ListBox
Control" topic in the Help menu.
ListBox Control Properties and Display Attributes
The following two tables describes several of the data properties and
display attributes of the ListBox control:
Data Property Description
----------------------------------------------------------------
ColumnCount Number of columns contained in the ListBox object.
RowSource Source of the values displayed in the ListBox object.
RowSourceType Data type of the values. For example, fields, array, list,
files, and list of fields are all valid data types.
ControlSource Where the value chosen by the user is stored. For example,
the value may be stored in a variable.
BoundColumn The column of a multiple-column array to return when the
user selects an object from the ListBox object.
Display
Attribute Description
---------------------------------------------------------------------
Moverbars Allows the rearrangement of values displayed in the
ListBox object.
Multiselect Allows users to choose multiple items from the
ListBox object.
FontName The font used in displaying the ListBox control's data.
FontItalic Turns on italic mode for the font specified in the
FontName property.
Step-by-Step Example
The following steps show how to create and add an array-driven ListBox to a
form.
- In the Command window, type:
CREATE FORM LISTTEST
- Adjust the form size so you have some working room. Click the form to
select it. Then right-click to bring up the Form sub-menu.
- Select the Data Environment menu pad. Right-click the Data Environment
window, and choose Add. In the Add Table or View dialog, choose Other.
From the SAMPLES\DATA directory, choose Customer, and click OK in
the Open dialog box. The Customer table should now be in the data
environment for the form. You can close the Data Environment for this
form.
- From the Form menu, choose New Property. Type in the array name as
MYARRAY(1). The array will now become a new property of the form. For
more information on adding properties scoped to a form or form set,
please see the topic "properties, scoped to form sets" in the Help menu.
- If the Form Properties sheet is not already on the screen, click the
form to select it. Then right-click to bring up the property sheet.
- Choose the Methods tab for the Form Properties sheet.
- Place the following SQL statement in the Form Load event:
SELECT cust_id, contact, phone FROM customer
INTO ARRAY Thisform.myarray
NOTE: The prefix "Thisform" in front of the array name is a
Critical and subtle point to remember about the scoping of member
arrays and variables within a form. If the SELECT statement is
simply done INTO ARRAY myarray, the array created by the SQL
statement will not have scope within the form itself. By prefacing
the array name with the "Thisform" clause, the results of the SQL
statement are directed into the array named myarray, which is part
of the form definition.
- Close the FORM1.LOAD screen.
- From the Form Controls toolbar, click the ListBox object and drag the
ListBox object onto the new form. Size the ListBox to occupy most of
the screen.
- With the ListBox selected, right-click the ListBox object, and choose
Properties.
- Select the Data tab, and set the following properties:
- BoundColumn = 1
This property governs which column of a multiple-element array is
returned to the List1.Value data element when a user selects a record
in the ListBox. In this example, you are creating a three-column
array, so you can use a value of 1, although 2 or 3 are also valid
entries for this property.
- NumberOfElements=ALEN(THISFORM.MYARRAY,1)
This property governs the total number of elements that will be
displayed in the ListBox. It is valid only for a RowSourceType of 5.
By using the =ALEN(THISFORM.MYARRAY,1) expression, you are telling
FoxPro to display all the values in the array as opposed to limiting
how many elements are displayed. Note that you must type the leading
equals sign.
The following information from the Visual FoxPro Help menu explains
the second, optional parameter used by the ALEN() function:
The second property of the ALEN() determines if ALEN() returns the
number of elements, rows or columns in the array. nArrayAttribute can
be 0, 1, or 2:
- 0 specifies to return the number of elements in the array.
Omitting nArrayAttribute is identical to specifying 0.
- 1 specifies to return the number of rows in the array.
- 2 specifies to return the number of columns in the array. If
the array is a one-dimensional array, ALEN() returns 0 (no
columns).
- RowSource = THISFORM.MYARRAY
This RowSource property tells Visual FoxPro that the data will be
coming from an object called MYARRAY.
- RowSourceType = 5 - Array
This RowSourceType property tells Visual FoxPro that the type of
object that contains the data is an array.
- From the ListBox Properties sheet, select the Layout tab, and set the
following properties:
- ColumnCount=3
This property governs how many elements of the array will be
displayed. Because the array that will drive this ListBox contains
three columns, the value of 3 is used. Array elements are displayed
in the order they appear in the array. For example, say you issue an
SQL SELECT statement such as this:
SELECT cust_id, contact, phone FROM CUSTOMER
Then the data in the ListBox will be displayed in that order
(cust_id, contact, phone).
- ColumnLines = .T.
This property determines whether or not to display bars between the
columns displayed in the array.
NOTE: Column lines are represented on the form during design time as
vertical bars. Because this is both a run-time and design-time
property, if this value is set to false, there will be NO visual
indicator of the number of columns defined for the ListBox object.
- ColumnWidths = 60,220,90
By default, the pixel is the unit of measurement on a Form.
- From the ListBox Properties sheet, select the Methods tab. Double-click
the word [Default] next to the words DblClick Event. This should open
up an editing window for the DblClick event.
In the editing window, type this command:
=MESSAGEBOX(THISFORM.LIST1.VALUE,64)
When you double-click an item in the list, your selection will be shown
in a message box with an OK button.
- Place a CommandButton control on the form. Place the following command
in the CLICK event:
RELEASE THISFORM
Change the caption to Quit.
- Save and run your form.
To get a feel for changing some of the properties on an active form, you
might want to try some of the following commands in the Command window:
LISTTEST.LIST1.MultiSelect=.T. && Turn on multiselect property.
LISTTEST.LIST1.FontName="MS Sans Serif" && Change font for ListBox.
LISTTEST.LIST1.FontItalic=.T. && Make the text italic.
LISTTEST.List1.BoundColumn=3 && Alter what column's data is
&& returned to List1.Value.
&& When you change this and then
&& double-click a record, the
&& data from the third column will
&& be returned to LIST1.VALUE.
Additional query words:
Multiselect multicolumn multi-select multi-column
Keywords : kbDesigner kbVFp300 kbVFp500 kbVFp600
Version : WINDOWS:3.0,3.0b,5.0,6.0
Platform : WINDOWS
Issue type : kbhowto
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