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This article mainly explains "VB development distributed how to understand", the content of the article is simple and clear, easy to learn and understand, now please follow the editor's ideas slowly in depth, together to study and learn "VB development distributed how to understand" it!

I. Overview

Activex is a set of standards developed by Microsoft for distributed computing, and its predecessor is known as ole automation. When distributed applications communicate over the network, activex can use two different mechanisms to respond to customer requests. One is called distributed component object pattern (dcom), which can only be used on windows nt and windows 95, and the other is remote Automation (remote automation), which can construct distributed applications in a 16-bit environment.

These two distributed mechanisms have extremely attractive characteristics: they are independent of the physical location of components. That is, when you construct an activex component, you don't need to know which machine it will be distributed on. The same component can be placed locally or distributed on other machines without having to recompile. In this way, we can easily adjust the distribution strategy of components according to the changes of network performance and network structure.

Of course, there are other advantages to using activex to build individual components of distributed applications:

The programming method of constructing remote components is exactly the same as constructing local components, without special engineering experience. You can use activex components to implement complex business rules on the server side. We have better means of programming, maintenance, and troubleshooting than using dbms (such as sql server) to do the same thing.

There are a large number of commercial components available. And there will be more and more such components. We only need to develop special business rules into components that can be used with purchased components.

II. Development and debugging

VB developing distributed components is the same as developing local components, and debugging can also be done locally, which is not discussed in this article. (you can see the example that comes with VB:\ sample\ clisvr\ booksale\ client\ book_cli.vbp client program;\ sample\ clisvr\ booksale\ client\ book_svr.vbp server program. When developing distributed server segment components, be aware of the following issues

The server-side project should be activex exe (an out-of-process activex component). It is also easy to understand that it is not possible to complete the same process on two machines, so it is not possible to use activex dll (in-process components).

Under the components section of the project properties dialog box, it should be set to remote server file. In this way, a vbr file is generated when the program is compiled, which is used when generating the installation disk. As we all know, the windows program is registered in the system registry, and this file is related to registration.

The class property should be set to mutiuse so that it can be used by multiple customer applications.

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