An extremely powerful feature of Visual FoxPro is the ability to create subclasses of the base controls. By creating one or more subclasses, you can customize the basic Visual FoxPro controls in almost any way that's required for your application. This ability extends to being able to create new objects or controls that combine the features of other controls. For example, the grid control in Visual FoxPro contains not only its own container, properties, and methods, but those of the objects that appear in the grid such as buttons, text boxes, and so on.

Similarly, by subclassing base controls, you can extend the capabilities of Visual FoxPro by creating objects that add new features to existing base classes, or that combine the capabilities of several objects. For example, you can add visual features such as frames or three-dimensional effects to a text box. Or you could combine an image control, buttons, and a text box to create a bitmap-viewing control in which users can move through a series of .bmp files. Creating custom classes in this way can help you manage company-wide development by allowing you to create standardized controls that appear in all your applications. For more information, see Object-Oriented Programming.

An alternative to creating a new control using subclasses in Visual FoxPro is to use an ActiveX control (.ocx file). These controls are created independently from Visual FoxPro, and can be integrated not only into Visual FoxPro, but into many other Windows applications as well.

In effect, ActiveX controls are off-the-shelf components that you can integrate seamlessly into your application. Using ActiveX controls provides several benefits:

• It saves you the time and effort required to create, test, and maintain a Visual FoxPro-specific control to accomplish the same tasks. The more capable the ActiveX control, the more time you save.
  
  
• Many ActiveX controls are already available from third-party suppliers to answer common application requirements. For example, if your application calls for you to display a calendar and allow users to choose dates on it, you can probably find an ActiveX control (perhaps several) that already manages this task.
  
  
• The same control can be used in multiple programs. For example, if it makes sense to do so, you can use the same ActiveX control in Visual FoxPro and Visual Basic. The same properties and methods are used in each case to manage the control, and the control will have the same appearance in all programs, making it easier for users to work with.
  
  
• ActiveX controls often provide access to Windows functionality that can otherwise be awkward or time-consuming to include using only Visual FoxPro tools. For example, you can find ActiveX controls that provide access to electronic mail (using Windows MAPI functions), to low-level Windows graphics functions, and so on. By including an ActiveX control, you can add these types of features to your application in a way that's easy to control using the ActiveX control's properties, methods, and events.
  
  

In short, using ActiveX controls enables you to extend your applications not only by integrating Windows-wide functionality, but by adding a common look-and-feel between your application and others in the same enterprise. For more information about using ActiveX controls, see Sharing Information and Adding OLE. For information about creating your own ActiveX controls, see Accessing the Visual FoxPro API.

A number of Visual FoxPro wizards allow you to integrate Visual FoxPro data with the functionality of other Windows programs. For example, you can send form letters to your customers by using the Mail Merge Wizard. When you run the wizard, you can specify a table or view that contains the Visual FoxPro data to use, and then either export the data to a suitable file format (such as comma-delimited) or specify that your word processing program use the Visual FoxPro OLE DB provider to access the data. If you use Microsoft Word, the wizard will even start the word processing program, create the blank merge document, and display the Mail Merge toolbar for you to link fields to your Visual FoxPro data.

Similarly, using Microsoft Excel and Microsoft Query, you can analyze your data using a pivot table, which summarizes data in columns and allows you to rearrange it to view it in different ways. By using the PivotTable Wizard in Visual FoxPro, you can use your application data as the source data for Microsoft Excel, and generate the pivot table in Microsoft Excel.

A more powerful way to interact with other applications is to use Automation. Using Visual FoxPro programs, you can access the objects exposed by other applications, and then control them by setting their properties and calling their methods. For example, Microsoft Excel exposes an application object as well as worksheets, columns, rows, and cells within the application object. You can directly manipulate any of these objects, including getting or setting data in them. In addition, you can usually control the application object using the full range of commands available in the program itself. For example, by managing the application object in Microsoft Excel, you can open, save, or print worksheets, invoke the Microsoft Excel chart wizard, and so on.

Automation is a particularly attractive and powerful way to work with Windows programs using Visual FoxPro for several reasons:

• You have direct access to the other program, including all its objects and commands.
  
  
• You can share data directly with the other program without having to export it or convert it to another format.
  
  
• You can control the other program using the familiar properties and methods model.
  
  
• The other program doesn't necessarily need to be visible to the user when you invoke it. For example, you can invoke Microsoft Excel, place some data into cells, run a complex calculation on the data, read the result, and then display it in Visual FoxPro, all without ever displaying Microsoft Excel. Your user would continue to see only Visual FoxPro, unless you explicitly wanted to display Microsoft Excel.
  
  
• The commands (methods and properties) to control the other program are embedded within familiar Visual FoxPro programs. You don't need to learn a different programming language in order to be able to control the other program.
  
  

Automation is particularly powerful because it's an open-ended method for working with other programs. In essence, Automation simply makes available to you the data and commands from other applications for you to use in the way best suited to your application.

A sample scenario illustrates how you can integrate several Windows programs. Imagine that you store your customer and sales data in Visual FoxPro. You'd like to create a sales report that summarizes quarterly sales.

One solution would be to use Automation to copy the Visual FoxPro sales data to cells in a Microsoft Excel worksheet. You can then invoke the Microsoft Excel chart wizard to create a chart of the data and copy it to the Windows Clipboard. Still using Automation, you can invoke Microsoft Word and create or open a sales report document (if you create it as a new document, you can insert standard text that you store in Visual FoxPro), and then paste in the chart you created in Microsoft Excel.

This is just one way you can use Automation to make Visual FoxPro part of an enterprise-wide solution. By becoming familiar with the objects and methods available in programs that you typically use, you can imagine many more ways to make each program enhance the capabilities of the other. For details about Automation, see "Manipulating Objects with Automation" Sharing Information and Adding OLE.