Hour 20. Controlling Other Applications Using Automation

In Hour 17, "Designing Objects Using Classes," you learned how to use classes to create objects. In that hour, I mentioned that objects could be exposed to outside applications ”Excel, for example, exposes most of its functionality as a set of objects. The process of using objects from another application is called Automation. The externally accessible objects of an application compose its object model. Using Automation to manipulate a program's object model enables you to reuse components . For instance, you can use Automation with Excel to perform complex mathematical functions using the code that's been written and tested within Excel, rather than having to write and debug the complex code yourself.

Programs that expose objects are called servers, and the programs that consume those objects are called clients . Creating automation servers requires advanced skills, including a very thorough understanding of programming classes. Creating clients to use objects from other applications, on the other hand, is relatively simple. In this hour, you'll learn how to create a client application that uses objects of an external server application.

The highlights of this hour include the following:

Creating a reference to an automation library
Creating an instance of an automation server
Manipulating the objects of an automation server

To understand Automation, you're going to build a Microsoft Excel client ”a program that automates Excel via Excel's object model.

This exercise is designed to work with Excel 2000 or Excel XP. If you don't have Excel installed on your computer, you won't be able to complete the exercise.

Create a new Windows Application named Automate Excel. Change the name of the default form to fclsMain, set its Text property to Automate Excel, and then set the entry point in Main() to reference fclsMain instead of Form1. Next, add a button to the form by double-clicking the Button item in the toolbox and set the button's properties as follows :

Property	Value
Name	`btnAutomateExcel`
Location	`96,128`
Size	`104,23`
Text	`Automate Excel`

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