Recipe Sharing a Thread Between Two Applications

The previous recipes motivated the use of multiple threads in a single application.The converse case is also sometimes useful: use of multiple applications in a single thread. For example, if two applications need to communicate between each other, they can do so using binders rather than the more complicated inter-process communication (IPC) pro-tocol.The steps are

1. Make sure each application, when packaged for release, is signed with the same key for security reasons.

2. Make sure each application is run with the same user ID. This is done by declaring the same attribute android:sharedUserId="my.shared.userid" in the ActivityManifest.xml for each application.

3. Declare each relevant activity or component to be run in the same process.This is done by declaring the same attribute android:process="my.shared.process-name" in the ActivityManifest.xml for each component.

These simple steps ensure the two components are run in the same thread and transparently share the same information. The more complex case where permissions cannot be shared is covered in the "Implementing a Remote Procedure Call" recipe in Chapter 11, "Advanced Android Development."

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