Choosing a Project Type

Any project that you create in Visual Basic can contain reusable classes. The project type determines how the classes are used. Before you create a class, think about the type of project in which it belongs.

There are seven types of projects you can create in Visual Basic. Table 20.1 lists these types and when to use them.

Table 20.1 - Types of Projects and Their Uses

Project Type	Public?	Use to Create
Standard .EXE	No	A general application that does not share components
ActiveX .EXE	Yes	A shared component that runs in a separate process
ActiveX DLL	Yes	A shared component that runs within the caller's process
ActiveX control	Yes	A visual component for use within Visual Basic, Visual C++, and other OCX-compliant applications
Add-In	Yes	A tool that can be loaded in the Visual Basic development environment
ActiveX document .EXE	Yes	An application that runs in Internet Explorer or other hosting environments
ActiveX document DLL	Yes	A shared component that runs within Internet Explorer

Of the project types listed in Table 20.1, only the Standard .EXE is completely private; that is, it does not provide classes for reuse in other applications. All other types of projects can contain both private and public classes.

This creates a special case for Standard .EXEs. With other project types, classes have an Instancing property that controls how new objects are created; with Standard .EXE projects, the Instancing property is not available - all classes are private. Table 20.2 shows what Instancing settings are available from different project types.

Table 20.2 - Available Instancing Property Settings by Project Type

Instancing Setting	Standard .EXE	ActiveX .EXE	ActiveX DLL	ActiveX Control	Add-In	Document .EXE	Document DLL
1 - Private	X	X	X	X	X	X	X
2 - PublicNotCreatable		X	X	X	X	X	X
3 - SingleUse		X			X	X
4 - GlobalSingleUse		X			X	X
5 - MultiUse		X	X		X	X	X
6 - GlobalMultiUse		X	X		X	X	X

Be sure to choose a project type that allows the type of classes you want to create. You can change project type at any time, but sometimes doing so means that other settings will change as well. The terms used in the Instancing settings list have special meanings:

• SingleUse classes create a new instance each time another application calls New or CreateObject to create an object.
• MultiUse classes create only one instance, regardless of how many times New or CreateObject are called.
• Global classes make their properties and methods available to other applications without a qualifying object name. Methods and properties defined for global objects look just like Visual Basic statements from within code. For example, mthTest.Average(1, 3, 5) can be written Average(1, 3, 5) if the class is global.