DOCERR: ListIndex (OutLine) Returns -1 If No Item Is Selected

The information in this article applies to:

• Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b

SUMMARY

Visual FoxPro Help says that the return value for the ListIndex (OutLine Control) Property is 0 if no item is selected. This is incorrect. The value returned if no item is selected is -1. It also says that the first index number that the ListIndex property can return is 1, which is also incorrect. The first index number that can be returned is 0.

MORE INFORMATION

The OutLine control is contained in the Msoutl32.ocx file located in the Windows\System subdirectory. Because .ocx files are written in the C language, the arrays they use start at zero. Therefore, the array that holds the values in the OutLine control that the ListIndex property references starts at zero. This referencing is different from the ListIndex property for a combo or list box where 0 is returned if no item is selected. This occurs because arrays in FoxPro start at 1.

Steps to Illustrate Behavior

1. Create a new form, and add a OLE Container control by moving it from the Form Controls toolbar to the form.

2. When the Insert Object dialog box appears, click Insert Control, and select the OutLine Control from the Control Type list box.

3. Add the following code to the Init event of the OutLine Control:

   THIS.ADDITEM("Colors",0) && This places the word Colors in the

      THIS.ADDITEM("Red",1)    && first element of the array followed
      THIS.ADDITEM("Blue",2)   && by Red, Blue, and Green to give
      THIS.ADDITEM("Green",3)  && a total of four elements in the array
                               && to be displayed in the OutLine control.
   
      THIS.INDENT(0) = 1       && This gives the word Colors an
      THIS.INDENT(1) = 2       && indention level of 1. These lines
      THIS.INDENT(2) = 2       && indent the words Red, Blue, and
      THIS.INDENT(3) = 2       && Green under the word Colors
                               && with an indention level of 2.
   
   

4. Place a text box on the form. In the ControlSource property, type:

   THISFORM.OLECONTROL1.LISTINDEX

5. In the Click event of the OutLine control, place the following code:

   THISFORM.TEXT1.VALUE = THISFORM.OLECONTROL1.LISTINDEX

6. Run the form. Note that the text box displays -1. After you click the word Colors, the value of the text box changes to 0. Click the plus sign to the left of the word Colors, and then click any item under it. The text box displays the ListIndex value of whatever item is selected. Remember that the text box will show a number that is one less than the position of the item selected in the OutLine control. That is because the first item's array element number has a value of 0, the second item is 1, the third item is 2, and so on.