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Do note that as with file picker providers, a contact provider needs to be ready to save its session
state when suspended such that it can restore that state when relaunched with
previousExecution-State set to terminated. Although not demonstrated in the sample, a real provider
app should save its current selections and viewing position within its list, along with whatever else, to
session state and restore that in its activated handler when necessary.
What We’ve Just Learned
• Contracts in Windows 8 provide the ability for any number of apps to extend system
functionality as well as extend the functionality of other apps. Through contracts, installing more
apps that support them creates a richer overall environment for users.
• The Share contract provides a shortcut means through which data from one app can be sent to
another, eliminating many intermediate steps and keeping the user in the context of the same
app. A source app packages data it can share when the Share charm is invoked; target apps
consume that data, often copying it elsewhere as in an email message, text message, social
networking service, and so forth.
• The Share target provides for delayed rendering of items (such as graphics), for long-running
operations (such as when it’s necessary to upload large data files to a service), and for providing
quicklinks to specific targets within the same app (such as frequent email recipients).
• The Search contract provides integration between an app and the Search charm. From the
charm users can search the current app as well as any others that support the contract, easily
viewing results from other apps without having to manually launch them or switch to them. The
search contract allows apps to also provide query suggestions and result suggestions.
• File type and URI scheme associations are how apps can launch other apps. an app’s
associa-tions are declared in its manifest allowing it to be launched to service those associations.
URI scheme associations are an excellent means for an app to provide workflow services to
others.
• Apps that implement the provider side of the file picker contract appear as choices within the file
picker UI. This is how apps can present data sources they manage as if they were part of the local
file system, even though they might exist in databases, online services, or other such locations.
To the user, the necessary transport considerations are transparent, and through the cached file
updater contract a provider app can also handle synchronization of local and remote copies of
the file.
• The contract for Contacts works similarly to the file picker but with information about people. A
consuming app can easily invoke the contact picker UI and any number of provider apps can
implement the other side of the contract to surface an address book, database, or other source
through that UI.
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