September 2009
The Android NDK provides tools that allow Android application developers to embed components that make use of native code in their Android applications.
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.
The NDK provides:
This release of the NDK supports the ARMv5TE machine instruction set and provides stable headers for libc (the C library), libm (the Math library), OpenGL ES 1.1 (3D graphics library), the JNI interface, and other libraries.
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.
Please note that the NDK does not enable you to develop native-only applications. Android's primary runtime remains the Dalvik virtual machine.
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.
It provides a set of system headers for stable native APIs that are guaranteed to be supported in all later releases of the platform:
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.
Important: With the exception of the libraries listed above, native system libraries in the Android platform are not stable and may change in future platform versions. Your applications should only make use of the stable native system libraries provided in this NDK.
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
<ndk>/docs/ directory. Included are these files:
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
<ndk>/docs/system/libc/ directory:
The NDK includes three sample Android applications that illustrate how to use native code in your Android applications:
hello-jni — A simple application that loads a string from
a native method implemented in a shared library and then displays it in the
application UI. two-libs — 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. san-angeles — A simple application that renders 3D
graphics through the native OpenGL ES APIs, while managing activity lifecycle
with a GLSurfaceView object. For more information, see Using the Sample Applications.
The sections below describe the system and software requirements for using the Android NDK, as well as platform compatibility considerations that affect appplications using libraries produced with the NDK.
<uses-library>
element in its manifest file, with an android:minSdkVersion attribute
value of "3" or higher. For example:
<manifest> ... <uses-sdk android:minSdkVersion="3" /> ... </manifest>
Additionally, if you use this NDK to create a native library that uses the
OpenGL ES APIs, the application containing the library can be deployed only to
devices running Android 1.6 or later. To ensure compatibility in this case,
the application must declare an android:minSdkVersion
attribute value of "4" or higher.
For more information about API Level and its relationship to Android platform versions, see Android API Levels.
Installing the NDK on your development computer is straightforward and involves extracting the NDK from its download package and running a host-setup script.
Before you get started make sure that you have downloaded the latest Android SDK 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 System and Software Requirements for the NDK, if you haven't already.
To install the NDK, follow these steps:
android-ndk-<version>. 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 <ndk>. <ndk>/build/host-setup.sh
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.
Once you have run the host-setup script, you are ready start working with the NDK.
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
<ndk>/docs/ directory. In particular, please read the
OVERVIEW.TXT document completely, so that you understand the intent of the NDK
and how to use it.
If you used a previous version of the NDK, take a moment to review the list of NDK changes in the CHANGES.TXT document.
Here's the general outline of how you work with the NDK tools:
<project>/jni/...<project>/jni/Android.mk to
describe your native sources to the NDK build system<ndk>/apps/<my_app>/Application.mk 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
<project>/jni/ folder and it specifies the path to the
application project that will receive the shared library built from the
sources.$ make APP=<my_app>
The build tools copy the stripped, shared libraries needed by your application to the proper location in the application's project directory.
For complete information on all of the steps listed above, please see the documentation included with the NDK package.
The NDK includes three sample applications that illustrate how to use native code in your Android applications:
hello-jni — A simple application that loads a string from
a native method implemented in a shared library and then displays it in the
application UI. two-libs — 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. san-angeles — A simple application that renders 3D
graphics through the native OpenGL ES APIs, while managing activity lifecycle
with a GLSurfaceView object. 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
<ndk>/apps/<app_name>/project/ and the C source for
each application is provided in
<ndk>/apps/<app_name>/project/jni/.
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:
$ make APP=hello-jni — compiles
<ndk>/apps/hello-jni/project/jni/hello-jni.c and outputs a
shared library to
<ndk>/apps/hello-jni/project/libs/armeabi/libhello-jni.so.
$ make APP=two-libs — compiles
<ndk>/apps/two-libs/project/jni/second.c and
first.c and outputs a shared library to
<ndk>/apps/two-libs/project/libs/armeabi/libtwolib-second.so.
Next, build the sample Android applications that use the shared libraries:
<ndk>/apps/<app_name>/project/. 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 Developing in
Eclipse.android tool to create
the build file for each of the sample projects at
<ndk>/apps/<app_name>/project/. Then set up an AVD, if
necessary, build your project in the usual way, and run it in the emulator.
For more information, see Developing in Other
IDEs.If you have questions about the NDK or would like to read or contribute to discussions about it, please visit the android-ndk group and mailing list.