Cross-app communication and plugin architecture in Android

A presentation by Siebe Sysmans.
This presentation was given for Mobel (http://www.mobel.io) and IT students.
Code: https://github.com/appfoundry/AndroidPluginArchitecture

Transcript

1. Android Plugin Architecture
   

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2. Cross-app communication
   

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3. Cross-app communication
   • Intent and BroadcastReceiver
   • ContentResolver and ContentProvider
   • Services

   …
   

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4. Android Plugin Architecture
   

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5. Android Plugin Architecture
   • Why?
   • User Plugin Discovery
   • Host App Plugin Discovery
   • Plugin Communication
   

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6. App Examples
   

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7. DashClock Widget
   

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8. DashClock Widget
   

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9. Muzei Live Wallpaper
   

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10. Muzei Live Wallpaper
    

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11. Why?
    

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12. Ecosystem-based marketing
    • Don’t create all your own plugins
    • Open up an API to extend your app
    • Indirectly promoting your app
    

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13. Business Model
    • Free app with basic functionality
    • Paid plugins
    

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14. Permission Mitigation
    • Standard Android is all or nothing
    • People might not install your permission rich app
    • Provide core app with less permissions
    • User can choose permissions by installing plugins
    (Before Android 6)
    

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15. User Plugin Discovery
    

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16. User Plugin Discovery
    • Hardcode references in core app
    • Link to a search term on Play Store
    • Download a JSON
    • Use a WebView
    • …
    

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17. App Plugin Discovery
    

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18. BroadcastReceiver
    Host app Plugin app
    BroadcastReceiver
    BroadcastReceiver
    Are there any plugins?
    Plugin app
    BroadcastReceiver
    

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19. BroadcastReceiver
    Host app Plugin app
    BroadcastReceiver
    BroadcastReceiver
    Yea, I’m a plugin!
    Plugin app
    BroadcastReceiver
    Yea, I’m a plugin!
    

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20. BroadcastReceiver
    • Not recommended
    • It wakes up every plugin app
    • Not sure when every plugin app responded
    

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21. PackageManager
    • Every plugin implements a custom intent action
    • PackageManager queries for every component
    using that custom action
    • Easily get metadata of that component
    

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22. Package Broadcasts
    • Android system sends package broadcasts
    • Host app checks if we are interested

    in that package change
    • Host app can update a live list of plugins
    

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23. Package Broadcasts
    Host app
    BroadcastReceiver
    ListView
    Android System
    App installs
    App replaces
    App deletes
    

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24. Package Broadcasts
    Host app
    BroadcastReceiver
    ListView
    Android System
    App installs
    App replaces
    App deletes PACKAGE_ADDED

    PACKAGE_REPLACED
    PACKAGE_REMOVED
    

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25. Package Broadcasts
    Host app
    ListView
    Android System
    App installs
    App replaces
    App deletes PACKAGE_ADDED

    PACKAGE_REPLACED
    PACKAGE_REMOVED
    Update
    

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26. Plugin Communication
    

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27. MetaData
    Great for getting static data
    • Plugin name
    • Plugin icon
    • Plugin api level
    

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28. Coding Example
    MetaData
    Using resources from other app
    PackageManager manager = getPackageManager();
    Resources pluginResources = manager.getResourcesForApplication("com.example.pluginapp");
    int drawableResID = pluginResources.getIdentifier("app_icon", "drawable", "com.example.pluginapp");
    Drawable drawable = pluginResources.getDrawable(drawableResID);
    

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29. BroadcastReceiver
    Host app Plugin app
    BroadcastReceiver
    BroadcastReceiver
    Provide me data
    

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30. BroadcastReceiver
    Host app Plugin app
    BroadcastReceiver
    BroadcastReceiver
    Here’s my data
    

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31. Remote Service Binding
    • Preferred way
    • Remote services found with PackageManager
    • Communication protocol using AIDL
    • Callback with Messenger for delayed responses
    

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32. Remote Service Binding - AIDL
    • All primitive types
    • int
    • long
    • char
    • …
    • String
    • Charsequence
    • List (ArrayList)
    • Map (HashMap)
    • Parcelable
    

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33. Remote Service Binding
    Host app Plugin app
    AIDL
    Compile
    Stub Stub
    Build
    

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34. Remote Service Binding
    Host app Plugin app
    Stub Stub
    Impl Impl
    Build
    

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35. Remote Service Binding
    Host app Plugin app
    Stub Stub
    Impl Impl
    Bind
    Run
    

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36. Remote Service Binding
    Host app Plugin app
    Stub Stub
    Impl Impl
    IPC
    Run
    

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37. GUI Plugins
    

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38. WebViews
    • Plugin provides data
    • Static URI using MetaData
    • Dynamic URI using IPC
    • Host has a WebView that loads the data
    • Easy
    • Not native
    • Security issues (javascript)
    

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39. RemoteViews
    • Native
    • Homescreen widgets
    • Lockscreen widgets
    • Notifications
    • Only basic View Widgets
    • Parcelable!
    

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40. Roll Your Own Parcelable
    • More flexible
    • A lot more work
    • Need to version your view building
    

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41. Some extra tips
    

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42. Some Extra Tips
    • Think about your versioning
    • Abstract to a library for distribution
    • Input validation in host
    • Make sure it’s secure
    • Don’t leak data

    →using signature level permissions
    

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43. Questions?
    Siebe Sysmans
    Consultant at AppFoundry
    siebe.sysmans@appfoundry.be
    @ThisIsSiebe
    

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