The sections below provide information and notes about successive releases of the NDK, as denoted by revision number.
Android NDK, Revision 4 (May 2010)
ndk-build build
command. ndk-gdb command.armeabi-v7a. The new ABI extends the existing armeabi
ABI to include these CPU instruction set extensions:
cpufeatures static library (with sources) that lets
your app detect the host device's CPU features at runtime. Specifically,
applications can check for ARMv7-A support, as well as VFPv3-D32 and NEON
support, then provide separate code paths as needed.hello-neon, that illustrates how to
use the cpufeatures library to check CPU features and then provide
an optimized code path using NEON instrinsics, if
supported by the CPU..apk.Bitmap objects from native
code.
Android NDK, Revision 3 (March 2010)
hello-gl2, that illustrates the use of
OpenGL ES 2.0 vertex and fragment shaders.
Android NDK, Revision 2 (September 2009)
Originally released as "Android 1.6 NDK, Release 1".
san-angeles, that renders 3D
graphics through the native OpenGL ES APIs, while managing activity
lifecycle with a GLSurfaceView object.
Android NDK, Revision 1 (June 2009)
Originally released as "Android 1.5 NDK, Release 1".
The Android NDK is a toolset that lets you embed components that make use of native code in your Android applications.
Android applications run in the Dalvik virtual machine. The NDK allows you to implement parts of your 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:
.apk) that can be deployed on Android devicesThe latest release of the NDK supports these ARM instruction sets:
Future releases of the NDK will also support:
ARMv5TE machine code will run on all ARM-based Android devices. ARMv7-A will
run only on devices such as the Verizon Droid or Google Nexus One that have a
compatible CPU. The main difference between the two instruction sets is that
ARMv7-A supports hardware FPU, Thumb-2, and NEON instructions. You can target
either or both of the instruction sets — ARMv5TE is the default, but
switching to ARMv7-A is as easy as adding a single line to the application's
Application.mk file, without needing to change anything else in the file. You
can also build for both architectures at the same time and have everything
stored in the final .apk. For complete information is provided in the
CPU-ARCH-ABIS.TXT in the NDK package.
The NDK provides stable headers for libc (the C library), libm (the Math library), OpenGL ES (3D graphics library), the JNI interface, and other libraries, as listed in the section below.
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:
cpufeatures
static library that lets your application code detect the target device's
CPU family and the optional features at runtime. 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 sample Android applications that illustrate how to use native code in your Android applications. 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-sdk>
element in its manifest file, with an android:minSdkVersion attribute
value of "3" or higher. For example:
<manifest> ... <uses-sdk android:minSdkVersion="3" /> ... </manifest>
android:minSdkVersion attribute value, as given in the table.
| OpenGL ES Version Used | Compatible Android Platform(s) | Required uses-sdk Attribute |
|---|---|---|
| OpenGL ES 1.1 | Android 1.6 and higher | android:minSdkVersion="4" |
| OpenGL ES 2.0 | Android 2.0 and higher | android:minSdkVersion="5" |
For more information about API Level and its relationship to Android platform versions, see Android API Levels.
<uses-feature> element in its manifest, with an
android:glEsVersion attribute that specifies the minimum OpenGl ES
version required by the application. This ensures that Android Market will show
your application only to users whose devices are capable of supporting your
application. For example:
<manifest> ... <uses-feature android:glEsVersion="0x00020000" /> ... </manifest>
For more information, see the <uses-feature>
documentation.
Bitmap pixel buffers, the application
containing the library can be deployed only to devices running Android 2.2 (API
level 8) or higher. To ensure compatibility, make sure that your application
declares <uses-sdk android:minSdkVersion="8" />attribute
value in its manifest.Installing the NDK on your development computer is straightforward and involves extracting the NDK from its download package. Unlike previous releases, there is no need to run 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>. You are now 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<project>/jni/Application.mk.$ cd <project> $ <ndk>/ndk-build
The build tools copy the stripped, shared libraries needed by your application to the proper location in the application's project directory.
.apk file. For complete information on all of the steps listed above, please see the documentation included with the NDK package.
The NDK includes 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. hello-gl2 — a simple application that renders a triangle
using OpenGL ES 2.0 vertex and fragment shaders.hello-neon — a simple application that shows how to use
the cpufeatures library to check CPU capabilities at runtime,
then use NEON intrinsics if supported by the CPU. Specifically, the
application implements two versions of a tiny benchmark for a FIR filter
loop, a C version and a NEON-optimized version for devices that support it.bitmap-plasma — a simple application that demonstrates
how to access the pixel buffers of Android Bitmap
objects from native code, and uses this to generate an old-school "plasma"
effect. For each sample, the NDK includes the corresponding C source code and the
necessary Android.mk and Application.mk files. There are located under
<ndk>/samples/<name>/ and their source code can be found under
<ndk>/samples/<name>/jni/.
You can build the shared libraries for the sample apps by going into <ndk>/samples/<name>/
then calling the ndk-build command. The generated shared libraries will be located under
<ndk>/samples/<name>/libs/armeabi/ for (ARMv5TE machine code) and/or
<ndk>/samples/<name>/libs/armeabi-v7a/ for (ARMv7 machine code).
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.