docs/html/sdk/ndk/1.5_r1/index.jd

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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 &mdash; 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>