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Skip to main content. Start your free trial. Show and hide more. Publisher resources Download Example Code. Table of contents Product information. Working with Outlook 1. E-Mail and Other Messaging 6. Working with Contacts The host will program against this view directly and never be aware there is an isolation boundary between it and its add-in or that the add-in may have a very different view of the host. The first step in using add-ins in your application is discovering them: the application needs a way to find the available add-ins and get enough information about them to decide which ones to load and activate.
Depending on the application, the host will typically perform this step at application start-up, when a document is loaded, or upon a user request. Some of the high-level discoverability requirements include the ability to find particular types of add-ins in a specified location, providing enough information to let the host or user decide which add-ins it wants to use without having to activate them first, and intelligently caching so that the list of available add-ins does not have to be recomputed, and make it possible for add-ins to update the cache at installation time.
To achieve these ends, you can follow the steps we took. First, define where you want to look for add-ins. In this sample, we expect the AddIns and components to be installed in the current directory, but often applications will choose several different locations for example, the user's application data directory.
Next, update your add-in store so that it is aware of newly installed add-ins and pipeline components. Our AddInStore class is used in determining what can connect to what.
This information makes up what we call the pipeline. The store contains all the components that make up the pipeline between the host and its add-ins. Update APIs and may also be updated at add-in installation time, using our command-line tool, in order to enhance the discovery startup performance. The following code checks to see if new AddIns have been installed.
If no new add-ins or pipeline components have been installed since this was last called, this returns very quickly:. Once the cache has been updated, the host will want to find all the available add-ins that can be connected to the view abstract base class that the host built against. This code looks for Calculator AddIns in our root directory and stores the results:.
The AddInStore. FindAddIns method takes in the type of add-in you are looking for and the path where they are stored and returns a collection of AddInTokens. It is important to note that no add-in assemblies have been loaded at this point and no add-in code has been executed.
In our calculator scenario, we built a ChooseCalculator method to display the tokens to the user, allowing them to select which they want to use:. Once the application has decided which add-ins it wants to use, it then needs to activate them. The host needs, from its perspective, an instance that implements the requested abstract base class that is, the view.
In reality, however, the host usually needs more than that: it really wants the add-in isolated from the host and other add-ins, and it wants to be able to sandbox that add-in with a particular permission set. An isolated add-in assembly may not directly access code or resources in another assembly. For those who are unfamiliar with AppDomains, you can think of them as lightweight processes. Typically the host will run its code in one AppDomain, usually the default AppDomain that is created when the runtime starts up, and will want each add-in to have its own AppDomain.
By isolating add-ins from the host and from each other, you gain several important advantages:. It is important to note, however, that when developing the host and the add-in itself you are programming directly against the abstract base classes that make up the host and add-in views and therefore you don't have to worry about the constraints of the isolation boundary. In this version, we support AppDomain level isolation and may add process level isolation in future versions.
For more information on using AppDomains as a security boundary for hosting untrusted add-ins. The host needs to consider the security context with which to load and activate the add-in. A host application may be running in full trust but may wish to run add-ins with less permission. The preexisting security and AppDomain creation APIs are very powerful and let you tweak many different settings as to how the AppDomain is sandboxed.
In most cases the host will want to grant the add-in either FullTrust, intranet, or Internet security settings and rely on the framework to decide what that means. Our APIs make it very easy to choose one of those three settings but we also give you the ability to fine-tune the setup parameters if needed.
Putting it all together in one line of code, you get the following, which activates the selected AddInToken in a new AppDomain and sandboxes the assembly in the internet zone:. This single line of code returns to the host an activated instance of the selected add-in.
So what happens behind the scenes to make this happen? Next, we give the code running in that AppDomain the security permissions appropriate for the specified security level in this case corresponding to the Internet permission set. Then we set the ApplicationBase to be the location of the actual add-in assembly, to allow it to find its dependencies and resources.
Finally, we hook up required pipeline components that connect the host to the add-in.
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