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for Microsoft® Office and .netAdd-in Express Home > Add-in Express for Office and .NET > Online Guide > What is ClickOnce ClickOnce overview
 ClickOnce is a deployment technology introduced in .NET Framework 2.0. A key goal of ClickOnce is to minimize the effort required to deploy and update Office applications. ClickOnce provides a trustworthy deployment model for users to be able to download and execute applications from centrally managed servers without requiring administrator privileges on the client machine. They are deployed in a safe manner that prevents ClickOnce deployed applications from interfering with or corrupting any other applications or data on the client. The ClickOnce technology can be applied to applications of Office 2010 - 2000.
Targeted to non-administrator-privileges installations the ClickOnce technology also allows updating your Office applications. Subject to many
restrictions, it isn't a panacea in any way. Say, if your prerequisites include .NET Framework 2.0 and the user doesn't have it installed, your
application (as well as an add-in) will not be installed without administrator privileges. In addition, ClickOnce will not allow installing shared
components, such as custom libraries. It is quite natural, though.
When applied to a Windows forms application, ClickOnce deployment implies the following steps:
Publishing an application
You deploy the application to any of the following locations: File System (CD/DVD included) or Web Site. The files include all application files
as well as application manifest and deployment manifest. The application manifest describes the application itself, including the assemblies, the
dependencies and files that make up the application, the required permissions, and the location where updates will be available. The deployment
manifest describes how the application is deployed, including the location of the application manifest, and the version of the application that
the user should run. The deployment manifest also contains an update location (a Web page or network file share) where the application checks for
updated versions. ClickOnce Publish properties are used to specify when and how often the application should check for updates. Update behavior
can be specified in the deployment manifest, or it can be presented as user choices in the application's user interface by means of the ClickOnce
APIs. In addition, Publish properties can be employed to make updates mandatory or to roll back to an earlier version.
Installing the application
The user clicks a link to the deployment manifest on a web page, or double-clicks the deployment manifest file in Windows Explorer.
In most cases, the end user is presented with a simple dialog box asking the user to confirm installation, after which installation proceeds
and the application is launched without further intervention. In cases where the application requires elevated permissions, the dialog box also
asks the user to grant permission before the installation can continue. This adds a shortcut icon to the Start menu and lists the application in
the Control Panel/Add Remove Programs. Note, it doesn't add anything to the registry, the desktop, or to Program Files. Also note, that the
application is installed into the ClickOnce Application Cache (per user).
Updating the application
When the application developer creates an updated version of the application, he or she also generates a new application manifest and copies
files to a deployment location—usually a sibling folder to the original application deployment folder. The administrator updates the deployment
manifest to point to the location of the new version of the application. When the user opens the deployment manifest, it is run by the ClickOnce
loader and in this way updates the application.
Useful resources:
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