cherry-pick fda3521e into froyo

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page.title=Android 1.5 NDK, Release 1

@jd:body

<h2 id="overview">What is the Android NDK?</h2>

<p>The Android NDK provides tools that allow Android application developers

to embed components that make use of native code in their Android applications.

</p>

<p>Android applications run in the Dalvik virtual machine. The NDK allows 

developers to implement parts of their applications using native-code languages 

such as C and C++. This can provide benefits to certain classes of applications, 

in the form of reuse of existing code and in some cases increased speed.</p>

<p>The NDK provides:</p>

<ul>

<li>A set of tools and build files used to generate native code libraries from C

and C++ sources</li>

<li>A way to embed the corresponding native libraries into application package

files (.apks) that can be deployed on Android devices</li>

<li>A set of native system headers and libraries that will be supported in all

future versions of the Android platform, starting from Android 1.5 </li>

<li>Documentation, samples, and tutorials</li>

</ul>

<p>This release of the NDK supports the ARMv5TE machine instruction set

and provides stable headers for libc (the C library), libm (the Math library), 

the JNI interface, and other libraries.</p>

<p>The NDK will not benefit most applications. As a developer, you will need 

to balance its benefits against its drawbacks; notably, using native code does 

not result in an automatic performance increase, but does always increase 

application complexity. Typical good candidates for the NDK are self-contained,

CPU-intensive operations that don't allocate much memory, such as signal processing,

physics simulation, and so on. Simply re-coding a method to run in C usually does 

not result in a large performance increase. The NDK can, however, can be 

an effective way to reuse a large corpus of existing C/C++ code.</p>

<p>Please note that the NDK <em>does not</em> enable you to develop native-only

applications. Android's primary runtime remains the Dalvik virtual machine.</p>

<h2 id="contents">Contents of the NDK</h2>

<h4>Development tools</h4>

<p>The NDK includes a set of cross-toolchains (compilers, linkers, etc..) that

can generate native ARM binaries on Linux, OS X, and Windows (with Cygwin)

platforms.</p>

<p>It provides a set of system headers for stable native APIs that are

guaranteed to be supported in all later releases of the platform:</p>

<ul>

<li>libc (C library) headers</li>

<li>libm (math library) headers</li>

<li>JNI interface headers</li>

<li>libz (Zlib compression) headers</li>

<li>liblog (Android logging) header</li>

<li>A Minimal set of headers for C++ support</li>

</ul>

<p>The NDK also provides a build system that lets you work efficiently with your

sources, without having to handle the toolchain/platform/CPU/ABI details. You

create very short build files to describe which sources to compile and which

Android application will use them — the build system compiles the sources

and places the shared libraries directly in your application project. </p>

<p class="caution"><strong>Important:</strong> With the exception of the

libraries listed above, native system libraries in the Android 1.5 platform are

<em>not</em> stable and may change in future platform versions.

Your applications should <em>only</em> make use of the stable native system

libraries provided in this NDK. </p>

<h4>Documentation</h4>

<p>The NDK package includes a set of documentation that describes the

capabilities of the NDK and how to use it to create shared libraries for your

Android applications. In this release, the documentation is provided only in the

downloadable NDK package. You can find the documentation in the

<code>&lt;ndk&gt;/docs/</code> directory. Included are these files:</p>

<ul>

<li>INSTALL.TXT &mdash; describes how to install the NDK and configure it for

your host system</li>

<li>OVERVIEW.TXT &mdash; provides an overview of the NDK capabilities and

usage</li>

<li>ANDROID-MK.TXT &mdash; describes the use of the Android.mk file, which

defines the native sources you want to compile</li>

<li>APPLICATION-MK.TXT &mdash; describes the use of the Application.mk file,

which describes the native sources required by your Android application</li>

<li>HOWTO.TXT &mdash; information about common tasks associated with NDK 

development.</li>

<li>SYSTEM-ISSUES.TXT &mdash; known issues in the Android system images 

that you should be aware of, if you are developing using the NDK. </li>

<li>STABLE-APIS.TXT &mdash; a complete list of the stable APIs exposed

by headers in the NDK.</li>

</ul>

<p>Additionally, the package includes detailed information about the "bionic"

C library provided with the Android platform that you should be aware of, if you

are developing using the NDK. You can find the documentation in the 

<code>&lt;ndk&gt;/docs/system/libc/</code> directory:</p>

<ul>

<li>OVERVIEW.TXT &mdash; provides an overview of the "bionic" C library and the 

features it offers.</li>

</ul>

<h4>Sample applications</h4>

<p>The NDK includes two sample Android applications that illustrate how to use

native code in your Android applications:</p>

<ul>

<li><code>hello-jni</code> &mdash; A simple application that loads a string from

a native method implemented in a shared library and then displays it in the

application UI. </li>

<li><code>two-libs</code> &mdash; A simple application that loads a shared

library dynamically and calls a native method provided by the library. In this

case, the method is implemented in a static library that is imported by the 

shared library. </li>

</ul>

<p>For more information, see <a href="#samples">Using the Sample

Applications</a>.</p>

<h2 id="requirements">System and Software Requirements</h2>

<p>The sections below describe the system and software requirements for using

the Android NDK, as well as platform compatibility considerations that affect

applications using libraries produced with the NDK. </p>

<h4>The Android SDK</h4>

<ul>

  <li>A complete Android SDK installation (including all dependencies) is

required.</li>

  <li>Android 1.5 SDK or later version is required.</li>

</ul>

<h4>Supported operating systems</h4>

<ul>

  <li>Windows XP (32-bit) or Vista (32- or 64-bit)</li>

  <li>Mac OS X 10.4.8 or later (x86 only)</li>

  <li>Linux (32- or 64-bit, tested on Linux Ubuntu Dapper Drake)</li>

</ul>

<h4>Required development tools</h4>

<ul>

  <li>For all development platforms, GNU Make 3.81 or later is required. Earlier

versions of GNU Make might work but have not been tested.</li>

  <li>For Windows, a recent release of <a

href="http://www.cygwin.com">Cygwin</a>, including both the gmake and gcc 

packages, is required. </li>

</ul>

<h4>Android platform compatibility</h4>

<ul>

  <li>The native libraries created by the Android NDK can only be used on

devices running the Android 1.5 platform version or later. This is due to 

toolchain and ABI related changes that make the native libraries incompatible

with 1.0 and 1.1 system images.</li>

  <li>For this reason, you should use native libraries produced with the NDK in

applications that are deployable to devices running the Android 1.5 platform

version or later. To ensure compatibility, an application using a native library

produced with the NDK must declare a <code>&lt;uses-library&gt;</code> element

in its manifest file, with the attribute

<code>android:minSdkVersion="3"</code>.</li>

</ul>

<h2 id="installing">Installing the NDK</h2>

<p>Installing the NDK on your development computer is straightforward and

involves extracting the NDK from its download package and running a host-setup

script. </p>

<p>Before you get started make sure that you have downloaded the latest <a

href="{@docRoot}sdk/index.html">Android SDK</a> and upgraded your applications

and environment as needed. The NDK will not work with older versions of the

Android SDK. Also, take a moment to review the <a href="#requirements">System

and Software Requirements</a> for the NDK, if you haven't already. </p>

<p>To install the NDK, follow these steps:</p>

<ol>

<li>From the table at the top of this page, select the NDK package that is

appropriate for your development computer and download the package.</li>

<li>Uncompress the NDK download package using tools available on your computer.

When uncompressed, the NDK files are contained in a directory called

<code>android-ndk-&lt;version&gt;</code>. You can rename the NDK directory if

necessary and you can move it to any location on your computer. This

documentation refers to the NDK directory as <code>&lt;ndk&gt;</code>.  </li>

<li>Open a terminal, change to the NDK directory, and run the host-setup script.

The script sets up your environment and generates a host configuration file used

later, when building your shared libraries. The path to the host-setup script

is:

<p><code>&lt;ndk&gt;/build/host-setup.sh</code></p>

<p>If the script completes successfully, it prints a "Host setup complete."

message. If it fails, it prints instructions that you can follow to correct any

problems. </p>

</li>

</ol>

<p>Once you have run the host-setup script, you are ready start working with the

NDK. </p>

<h2 id="gettingstarted">Getting Started with the NDK</h2>

<p>Once you've installed the NDK successfully, take a few minutes to read the

documentation included in the NDK. You can find the documentation in the

<code>&lt;ndk&gt;/docs/</code> directory. In particular, please read the

OVERVIEW.TXT document completely, so that you understand the intent of the NDK

and how to use it.</p>

<p>Here's the general outline of how you work with the NDK tools:</p>

<ol>

<li>Place your native sources under

<code>&lt;ndk&gt;/sources/&lt;my_src&gt;/...</code>. If you want, you can place

a symlink to your sources, rather than the sources themselves. The sources you

reference here are not strictly associated with a specific shared library or

Android application. Instead, they are accessible to any build configuration and

can be used to produce any number of shared libraries that can be used by any

Android application.</li>

<li>Create <code>&lt;ndk&gt;/sources/&lt;my_src&gt;/Android.mk</code> to

describe your native sources to the NDK build system</li>

<li>Create <code>&lt;ndk&gt;/apps/&lt;my_app&gt;/Application.mk</code> to

describe your Android application and native sources it needs to the NDK build

system. This file sets up the link between an Android SDK application project

and any number of shared libraries defined in the

<code>&lt;ndk&gt;/sources/</code> folder and it specifies the path to the

application project that will receive the shared library built from the

sources.</li>

<li>Build your native code by running this make command from the top-level NDK

directory:

<p><code>$ make APP=&lt;my_app&gt;</code></p>

<p>The build tools copy the stripped, shared libraries needed by your

application to the proper location in the application's project directory.</p>

</li>

<li>Finally, compile your application using the SDK tools in the usual way. The

SDK build tools will package the shared libraries in the application's

deployable .apk file. </p></li>

</ol>

<p>For complete information on all of the steps listed above, please see the

documentation included with the NDK package. </p>

<h2 id="samples">Using the Sample Applications</h2>

<p>The NDK includes two sample applications that illustrate how to use native

code in your Android applications:</p>

<ul>

<li><code>hello-jni</code> &mdash; A simple application that loads a string from

a native method implemented in a shared library and then displays it in the

application UI. </li>

<li><code>two-libs</code> &mdash; A simple application that loads a shared

library dynamically and calls a native method provided by the library. In this

case, the method is implemented in a static library imported by the shared

library. </li>

</ul>

<p>For each sample, the NDK includes an Android application project, as well as

the corresponding C source code and the necessary Android.mk and Application.mk

files. The application projects are provided in

<code>&lt;ndk&gt;/apps/&lt;app_name&gt;/project/</code> and the C source for

each application is provided in

<code>&lt;ndk&gt;/sources/samples/&lt;library&gt;/</code>.</p>

<p>Once you have installed the NDK, you can build the shared libraries from the

NDK by using these commands from the root of the NDK directory:</p>

<ul>

<li><code>$ make APP=hello-jni</code> &mdash; compiles

<code>&lt;ndk&gt;/sources/samples/hello-jni/hello-jni.c</code> and outputs a

shared library to

<code>&lt;ndk&gt;/apps/hello-jni/project/libs/armeabi/libhello-jni.so</code>.

</li>

<li><code>$ make APP=two-libs</code> &mdash; compiles

<code>&lt;ndk&gt;/sources/samples/two-libs/second.c</code> and

<code>first.c</code> and outputs a shared library to

<code>&lt;ndk&gt;/apps/two-libs/project/libs/armeabi/libtwolib-second.so</code>.

</li>

</ul>

<p>Next, build the sample Android applications that use the shared

libraries:</p>

<ul>

<li>If you are developing in Eclipse with ADT, use the New Project Wizard to

create a new Android project for each sample, using the "Import from Existing

Source" option and importing the source from 

<code>&lt;ndk&gt;/apps/&lt;app_name&gt;/project/</code>. Then, set up an AVD, if

necessary, and build/run the application in the emulator. For more information

about creating a new Android project in Eclipse, see <a

href="{@docRoot}guide/developing/eclipse-adt.html">Developing in

Eclipse</a>.</li>

<li>If you are developing with Ant, use the <code>android</code> tool to create

the build file for each of the sample projects at

<code>&lt;ndk&gt;/apps/&lt;app_name&gt;/project/</code>. Then set up an AVD, if

necessary, build your project in the usual way, and run it in the emulator. 

For more information, see <a

href="{@docRoot}guide/developing/other-ide.html">Developing in Other

IDEs</a>.</li>

</ul>

<h2>Discussion Forum and Mailing List</h2>

<p>If you have questions about the NDK or would like to read or contribute to

discussions about it, please visit the <a

href="http://groups.google.com/group/android-ndk">android-ndk</a> group and 

mailing list.</p>

sdk.redirect=true

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@jd:body

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