Purpose of this Document

This document is designed as part of a series of demo script documents to assist customers who are evaluating Microsoft® Visual FoxPro™ 5.0. It can be used by an individual developer learning a new feature in Visual FoxPro 5.0; or as the basis for a demo shown to other developers and software tools evaluators. This demo script requires Visual FoxPro 5.0 to be installed. Questions about this demo script should be directed via email to foxmktg@microsoft.com.

Introduction

ActiveX™ controls (formerly known as OLE controls) are reusable software components that can be added to existing applications with minimal additional coding. Using ActiveX controls, developers can add unique functionality to their applications using prebuilt and pretested components. With over 2,000 ActiveX controls currently available, Visual FoxPro developers can access a rich inventory of components to extend and enhance their applications (this capability is demonstrated in the documents entitled "Demo Script: Using the ActiveMovie Control in Visual FoxPro 5.0" and "Demo Script: Using the ProgressBar Control in Visual FoxPro 5.0" available from the same location as this document). Developers can use the tools in Microsoft Visual Studio 97™ or Visual Basic® Control Creation Edition to create their own redistributable ActiveX controls.

Visual FoxPro 5.0 further extends the power of ActiveX controls by enabling the use of ActiveX controls in Visual FoxPro classes. A control's methods and properties may be manipulated, adding binding to specific data, for example, and then saved and reused in a Visual FoxPro class library. This approach speeds development and simplifies application maintenance.

This paper shows you how to demonstrate subclassing an ActiveX control in Visual FoxPro 5.0. You will take the Calendar control, which is not inherently data bound and, through code, bind it to a date column in a table.

Show that the Calendar Control is not Data Bound

Create a new form by typing create form in the Command window. In the form's Data Environment add the Orders table. You can use \Vfp\Samples\Data\Orders.dbf.

The Visual FoxPro Data Environment is a central design surface used with Forms and Reports where all major elements of data access can be manipulated. This includes all of the tables, indexes, relationships, defaults, rules, triggers, etc., associated with the form or report. In addition, the developer can drag and drop fields and even entire tables from the Data Environment window to the form or report, speeding and simplifying form creation.

Drag a few of the fields from the Orders table onto the form. Include the field order_date.

In the Form Controls toolbar click on the View Classes button and then choose Add from the popup menu. In the Open dialog locate the file \Vfp\Samples\Classes\Buttons.vcx and select it. The toolbar will change to show the classes in this class library, which contains various buttons for use on forms. Add the vcr class to the form. This provides generic navigation buttons and will allow you to scroll from record to record.

Click on the View Classes button and choose Standard from the popup menu. This will set the toolbar back to its default.

Click on the OLE Container Control button. Position the mouse cursor where you want the control to be and then drag until you have a rectangle. In the Insert Object dialog choose Insert Control. The Control Type list then shows all of the ActiveX controls registered on your machine. Choose Calendar Control from the list and then choose OK. Resize the control on the form so you can see the whole calendar.

In the Properties window notice that there are properties for Day, Month, and Year but there is no ControlSource property for the Calendar control. You would like to able to bind the Calendar control directly to the order_date column, but you can't.

Run the form and save it as Calendar.scx. As you scroll from record to record you will see that the calendar displays today's date, and never changes. Close the form.

Create the Calendar Control Subclass

Create a new class by typing create class in the Command window. In the New Class dialog enter databoundcalendar as the name of the class. Choose OLEControl from the Based On list. Then store the new class in the file Activex.vcx. Choose OK.

By encapsulating the control in a Visual FoxPro class, you are creating a reusable object that inherits the full power of the Visual FoxPro object oriented architecture. That is, you may reuse the object in many places, even alter its behavior with each use, and still maintain a link back to the base object. This makes global changes and maintenance of your objects much simpler than ever before. (For more information on the object oriented features in Visual FoxPro 5.0, please see the white paper entitled, "Creating Reusable Classes with Visual FoxPro," found on the Visual FoxPro Web site.)

When the New Class dialog is closed, the Class Designer is opened and the Insert Object dialog appears. In the Insert Object dialog choose Insert Control. Choose Calendar Control from the Control Type list and then choose OK. Resize the control in the Class Designer so you can see the whole calendar.

Choose New Property from the Class menu and add a property called date_column to the class. Choose New Method from the Class menu and add a method called RefreshDisplay.

Add custom code to the Calendar control to make it data bound

Add the following code to the RefreshDisplay method. This code will set the Month, Day, and Year properties of the Calendar control based on the value in the date field used to bind the control.

* What column is the control bound to?
cColumn = This.date_column

* If it is bound to a column
IF NOT EMPTY(cColumn)
    * Set the Month, Day, and Year properties of the 
    * calendar control to the Month, Day, and Year
    * of the date column it is bound to
    This.Month = Month(&cColumn)
    This.Day = Day(&cColumn)
    This.Year = Year(&cColumn)
ENDIF

* What column is the control bound to?
cColumn = This.date_column

* Construct a Visual FoxPro style date from the Month,
* Day, and Year properties of the Calendar
dValue = CTOD(ALLTRIM(STR(This.Month)) + "/" + ;
              ALLTRIM(STR(This.Day)) + "/" + ;
              ALLTRIM(STR(This.Year)))

* If the Calendar is bound to a column
IF NOT EMPTY(cColumn)
    * Update the value of the date field with the date
    * derived from the Calendar control
    Replace &cColumn With dValue
ENDIF

ThisForm.Refresh

* Run the refresh method of the Calendar control,
* which will update the date in the Calendar
ThisForm.ocxCalendar.RefreshDisplay