One scenario people want to support is to have multiple versions of the same application installed to a single machine/user’s account. The guidance I put together for patterns and practices has a walkthrough of setting this up. For example, say you have a version 22.214.171.124 of an application that is your production version, and you publish a new beta version (126.96.36.199) that you want a limited set of users to access, but those same users need to be able to run both production and beta side by side through ClickOnce on their machines (perhaps for feature comparison testing).
The first step is that you will need to have different deployment manifests for the multiple versions you want a single user to run. You direct the user to launch from each URL to the different deployment manifests and they will get a separate installation on their machine… or will they? The answer depends on a hidden aspect of the ClickOnce runtime regarding what the runtime considers a unique identity for an installed application.
If you are not familiar with the things that ClickOnce does under the covers to install an application on a client machine, it downloads and caches the deployment manifest, the application manifest, and all of the application files. Those manifests have to be signed by a publisher certificate that is cryptographically unique. Additionally, the installed application has a product name that gets embedded in the deployment manifest.
You might be tempted, as I was, to think that a unique product name, combined with a separate deployment manifest would be sufficient to make the client machine treat those installs as separate and distinct (such as setting the product names to “MyApp” and “MyApp – Beta”). Unfortunately you would be wrong, as I was.
There is actually a separate piece of information that the ClickOnce runtime uses to distinguish one application from another – the application identity is set by an identity set for the deployment manifest itself. This identity is normally created by Visual Studio when publishing and is set to the deployment manifest name (i.e. WindowsApplication1.application). You do not have control from Visual Studio to set this to anything else. Through the mageui.exe SDK tool, or better yet my Manifest Manager Utility included with the patterns and practices guidance, you can set this application identity to any string that you like to uniquely identify multiple published versions of a single application.
So to address the scenario presented earlier, you can simply set the application identity to MyApp for one version and MyApp-Beta for the other version, and you will be able to side-by-side install those two copies of the app on the same machine.