BUG: ListBox Control Scrolls Slowly

• Microsoft Visual FoxPro for Macintosh, version 3.0b

SYMPTOMS

When scrolling with the scroll bar in the ListBox control of Visual FoxPro, the scrolling speed is unreasonably slow. The Visual FoxPro ListBox may be many times slower than the @...GET-List of version 2.6. The scrolling speed of the ListBox is not dependent on the RowSourceType of the control or the size of the data set being scrolled.

WORKAROUND

Following are two workarounds for this behavior:

1. Recreate a ListBox-like object by subclassing a grid with the following properties:

   ColumnCount = 1

      DeleteMark   = .F.
      RecordMark   = .F.
      ScrollBars   = 2 - Vertical
      HeaderHeight = 0
      GridLines    = 0 - None
      RowHeight    = FontSize + 2
   
      The result will be similar in function to a ListBox and will scroll
      considerably faster with the scroll bar. However, if you are using
      repeated arrow keys to scroll, the grid is slower than the ListBox.
   
      One limitation of this approach is the limited selection of
      RecordSourceTypes of the grid as compared to the RowSourcetypes of the
      ListBox. The following tables illustrate this:
   
      Grid RecordSourceTypes:
   
         0 - Table
         1 - Alias
         2 - Prompt
         3 - Query (.QPR)
   
      ListBox RowSourceTypes:
   
         0 - None
         1 - Value
         2 - Alias
         3 - SQL Statement
         4 - Query (.QPR)
         5 - Array
         6 - Fields
         7 - Files
         8 - Structure
         9 - Popup
   
   

2. Define and activate a POPUP.

STATUS

Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

The following table illustrates the difference in scrolling speed. The test case used a ListBox sized to show 10 rows and populated with the company field from a customer table in the Visual FoxPro:Samples:Data folder. The customer table contains 91 records. The Time column reflects the time necessary to scroll via the down arrow from top to bottom:

   Machine              Product                  Time     Rate (r/s)
   -------------------- ---------------------    -------- ----------

   Power Mac 9500/132   Visual FoxPro/Mac 3.0     5.5      16.5
   Power Mac 9500/132   FoxPro/Mac 2.6            0.9     102.0
   Power Mac 7100/66    Visual FoxPro/Mac 3.0    26.0       3.5
   Power Mac 7100/66    FoxPro/Mac 2.6            2.8      32.5
   GateWay Pentium120   Visual FoxPro/Win 3.0     0.8     115.0

   Machine Details:

   - Power Mac 9500/132 32MB, VM 40MB, 7.5.3, ATI XClaim GA 4MB-
     1024x768xMillions

   - Power Mac 7100/66 AV 16MB, 24MB VM, 864x624xThousands

   - GateWay Pentium120, Windows NT Server 3.51,SP3, 32MB, 44 MB Swap,
     ATI PCI Video 2MB-1024x768x256