Click-Once Deployment

Click Once is a technology provided by Microsoft that allows easy application deployment over a network (including the Internet). ClickOnce has a lot of internal logic that is able to automatically communicate with our Servers to check if a new version of the software is available and update itself to the latest version accordingly. ClickOnce also has the added benefit that the users do not need Administrator privileges in order to install/use the software as ClickOnce deploys all the required software within the individual users Profile within Windows itself.

Some system administrators, however, lock down machines even more that the norm and this can cause issues with ClickOnce. The following information should help to explain what happens with ClickOnce, where all the files are stored and what system administrators can do if they have issues running our software deployed using ClickOnce.

Hard Drive Access
As stated above, ClickOnce does not require the user to have administrator privileges on their local machine to install or run ClickOnce deployed software. They do, however, need full read/write access to their own profile configuration that is stored with Windows. This is generally found in C:\Document and Settings\{UserName} on Windows XP and C:\Users\{UserName} on Windows Vista and Windows 7. When a ClickOnce application is installed, it is downloaded into the \Local Settings\Apps\2.0 directory within each users profile. The software is run from this location and stores any data files, or output logs to these directories. The directory names within the Apps/2.0 directory are auto generated by each workstation and never match from one workstation to the next (the name of the directory is generated by an internal algorithm dependant on time of day, size of install etc)

More than one user on one machine
Due to the directory structure outlined above, each user of a machine must have the software installed for their own use. So if the installation has already occurred for ‘Jane’, if ‘David’ logs in under his own name, he wont have the files within his profile so the installation from our website must occur again to allow ‘David’ to run the software.

Start Menu
Each user has a profile level Start Menu structure. If the ClickOnce deployment installs items into the Start Menu, they will only be visible to that user. Administrators should NOT move these shortcut links to the {Default User} or {All User} Start Menus as the software will no longer run correctly for each user of the machine. As stated in Hard Drive Access, each user will have a different directory name where the software is stored within the Apps/2.0 directory and each shortcut is programmed internally to point to each users unique directory name within their profile - moving the Start Menu items will cause failure as user ‘David’ is still unable to see user ‘Jane’ Apps/2.0 directory.


Additional Information about ClickOnce can be found on Microsoft and Wikipedia


C:\Navitas Directory
For many of our solutions we require some additional files to be stored within the C:\Navitas directory on the local machine. Whenever this occurs, Navitas provides a separate ‘Integrator’ installation file. This ‘integrator’ installation is only required to be run ONCE per workstation, but must be run when logged in as an administrator. Once this installation has occurred, the administrator should log out and then log back in as the actual user to proceed with the ‘normal’ ClickOnce application installation.

Proxy Cache Issues
Many network administrators will utilise Proxy servers to control access to internet content. Administrators also employee Caching mechanisms in an attempt to reduce internet traffic. These caching systems copy any accessed websites to a local server so that anyone requesting access to the same website in future only has to get it from the server and not go out to the internet itself. Caching of websites deploying Click Once applications cause issues when any new versions of our applications are deployed as workstations ‘behind’ the proxy will not detect a new version has been deployed. It is a requirement that any administrators utilising caching or proxies ensure that our clickonce servers are not cached to ensure all requests are sent directly to our website and all new versions of our software are able to download correctly.

Clearing the ClickOnce Cache
From time to time the ClickOnce cache can become corrupted and must be cleared in order for the application to continue to work. This is a simple two step process

  1. Navigate to the users ClickOnce cache directory located on the local workstation in the C:\Users\{username}\AppData\Local\Apps\2.0 directory
  2. Delete the two folders that appear in the above directory

Next time the user clicks the toolbar button in the GDS to launch the application they will be prompted to reinstall the software and it should start working again.

NB: A known issue has been identified where users of AVG Anti Virus software are not able to run ClickOnce software after a particular update was performed to AVG. To resolve the issue the above procedure can be used to force a fresh install of our click once software (this should only need to be performed ONCE per workstation / user)

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