| Microsoft can't seem to settle on a deployment technology. Before .NET, serious developers were forced to use third-party applications to build installation programs. Then Microsoft introduced Windows Installer Technology, where developers created an MSI file that installed an application. With Visual C# 2005, Microsoft has introduced yet another technology: ClickOnce. ClickOnce technology has its drawbacks, mostly in its lack of flexibility, but ClickOnce does have some significant improvements over earlier technologies. Many of the improvements will be appreciated mostly by experienced developers who have been battling install technology for some time; they might not make a lot of sense to you. This hour covers the highlights of ClickOnce technology. After you understand what the ClickOnce technology offers, I'll walk you through creating a ClickOnce program that will install your Picture Viewer program on a user's computer. The following points are highlights of the new ClickOnce technology: ClickOnce is designed to bring the ease of deploying a web application to the deployment of desktop applications. Traditionally, to distribute a desktop application you had to touch each and every client computerrunning the setup program and installing the appropriate files. Web applications, on the other hand, only need to be updated in one place: on the web server. ClickOnce provides desktop applications with update functionality similar to web applications. Applications deployed with ClickOnce can update themselves. They can check the Web for a newer version and install the newer version automatically. ClickOnce programs have the capability to update only necessary files. With previous installation technologies, entire applications had to be reinstalled to be updated. ClickOnce allows applications to install their components in such a way that they don't interfere with other installed applications. In other words, they are self-contained applications. With Windows Installer deployments (that is, the "old way"), applications shared components such as custom controls. If one application mistakenly installed an older version of a component, deleted a component, or installed an incompatible version of a component, it would break other installed applications that used the shared component. ClickOnce programs do not require the user to have administrative permissions. With Windows Installer deployments, users had to have administrative permissions to install an application. Trust me, this is a serious issue, and I'm glad to see ClickOnce address this. A ClickOnce application can be installed in one of three ways: from a web page, from a network file share, or from media such as a CD-ROM. A ClickOnce application can be installed on a user's computer, so it can be run when the user is offline, or it can be run in an online-only mode, where it doesn't permanently install anything on the user's computer.
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