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分类: LINUX
2009-06-30 08:38:18
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June 2009
The Android NDK is a companion tool to the Android SDK that lets Android application developers build performance-critical portions of their apps in native code. It is designed for use only in conjunction with the Android SDK, so if you have not already installed the Android 1.5 SDK, please do so before downloading the NDK. Also, please read What is the Android NDK? to get an understanding of what the NDK offers and whether it will be useful to you.
Select the download package that is appropriate for your development computer.
Platform Package Size MD5 ChecksumWindows | 22500667 bytes | e5c53915903d8b81f3e2ea422e2e2717 | |
Mac OS X (intel) | 17215303 bytes | 1931f0e182798a4c98924fd87380b5b8 | |
Linux 32/64-bit (x86) | 16025885 bytes | 80a4e14704ca84c21bf1824cb25fbd8b |
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), 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 1.5 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 two 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.
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:
<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.
Here's the general outline of how you work with the NDK tools:
$ make 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 two sample applications that illustrate how to use native code in your Android applications:
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/
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:
Next, build the sample Android applications that use the shared libraries:
If you have questions about the NDK or would like to read or contribute to discussions about it, please visit the group and mailing list.