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      1 Platform Library Example
      2 ~~~~~~~~~~~~~~~~~~~~~~~~
      3 
      4 
      5 This directory contains a full example of writing your own Android platform
      6 shared library, without changing the Android framework.  It also shows how to
      7 write JNI code for incorporating native code into the library, and a client
      8 application that uses the library.
      9 
     10 This example is ONLY for people working with the open source platform to
     11 create a system image that will be delivered on a device which will include
     12 a custom library as shown here.  It can not be used to create a third party
     13 shared library, which is not currently supported in Android.
     14 
     15 To declare your library to the framework, you must place a file with a .xml
     16 extension in the /system/etc/permissions directory with the following contents:
     17 
     18 <?xml version="1.0" encoding="utf-8"?>
     19 <permissions>
     20     <library name="com.example.android.platform_library"
     21             file="/system/framework/com.example.android.platform_library.jar"/>
     22 </permissions>
     23 
     24 There are three major parts of this example, supplying three distinct
     25 build targets and corresponding build outputs:
     26 
     27 
     28 com.example.android.platform_library
     29 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     30 
     31 The top-level Android.mk defines the rules to build the shared library itself,
     32 whose target is "com.example.android.platform_library".  The code for this
     33 library lives under java/.
     34 
     35 Note that the product for this library is a raw .jar file, NOT a .apk, which
     36 means there is no manifest or resources associated with the library.
     37 Unfortunately this means that if you need any resources for the library, such
     38 as drawables or layout files, you will need to add these to the core framework
     39 resources under frameworks/base/res.  Please make sure when doing this that
     40 you do not make any of these resources public, they should not become part of
     41 the Android API.  In the future we will allow shared libraries to have their
     42 own resources.
     43 
     44 Other than that, the library is very straight-forward, and you can write
     45 basically whatever code you want.  You can also put code in other Java
     46 namespaces -- the namespace given in the <library> tag above is just the
     47 public unique name by which clients will link to your library, but once this
     48 link happens all of the Java namespaces in that library will be available
     49 to the client.
     50 
     51 
     52 libplatform_library_jni
     53 ~~~~~~~~~~~~~~~~~~~~~~~
     54 
     55 This is an optional example of how to write JNI code associated with a
     56 shared library.  This code lives under jni/.  The jni/Android.mk file defines
     57 the rules for building the final .so in which the code lives.  This example
     58 provides everything needed to hook up the native code with the Java library
     59 and call through to it, plus a very simple JNI call.
     60 
     61 
     62 PlatformLibraryClient
     63 ~~~~~~~~~~~~~~~~~~~~~
     64 
     65 This shows an example of how you can write client applications for your new
     66 shared library.  This code lives under client/.  Note that the example is
     67 simply a regular Android .apk, like all of the other .apks created by the
     68 build system.  The only two special things needed to use your library are:
     69 
     70 - A LOCAL_JAVA_LIBRARIES line in the Android.mk to have the build system link
     71 against your shared library.
     72 
     73 - A <uses-library> line in the AndroidManifest.xml to have the runtime load
     74 your library into the application.
     75