JNI (2) Android NDK environment establishment and use

NDK interacts with C/C ++ through Java's Jni. If it doesn't work with Jni, you can check out what I 've previously compiled. <JNI (1) interaction between Java and C ++> 1. Build an NDK development environment 2. How to Use NDK for development

I. Build an NDK Development Environment1. Download the right NDK version of the platform. Download URL:Http://developer.android.com/tools/sdk/ndk/index.htmlFor Windows, you no longer need to download Cygwin. You can download NDK directly and decompress it. 2. NDK-contained libc (C library) headers libm (math library) headers JNI interface headers libz (Zlib compression) headers liblog (Android logging) header OpenGL ES 1.1 and OpenGL ES 2.0 (3D graphics libraries) headers libjnigraphics (Pixel buffer access) header (for Android 2.2 and above ). A Minimal set of headers for C ++ support OpenSL ES native audio libraries Android native application APIS3. NDK is worth a little time. the Android NDK Overview (overview.html in the ndkdirectory) provides a clear description of how to use NDK for development. b. sample Code under the samples directory.
II. How to Use NDK for developmentGetting Started with the NDK on the official website

Place your native sources under <project>/jni /... create <project>/jni/Android. mk to describe your native sources to the NDK build systemOptional: Create <project>/jni/Application. mk. build your native code by running the 'ndk-build' script from your project's directory. it is located in the top-level NDK directory: cd <project> <ndk>/ndk-buildThe build tools copy the stripped, shared libraries needed by your application to the proper location in the application's project directory. 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.

Example based on Hello-jni in NDK 1. Use Jni Android files

Package com. xcl. jnidemo5;/*** demonstrate NDK development ** author: xcl * date: 2014-3-20 */import android. OS. bundle; import android. app. activity; import android. view. menu; import android. widget. textView; public class MainActivity extends Activity {@ Overrideprotected void onCreate (Bundle savedInstanceState) {super. onCreate (savedInstanceState); // setContentView (R. layout. activity_main); TextView TV = new TextView (this); TV. setText (stringFromJNI (); setContentView (TV) ;}@ Overridepublic boolean onCreateOptionsMenu (Menu menu) {// Inflate the menu; this adds items to the action bar if it is present. getMenuInflater (). inflate (R. menu. main, menu); return true;} public native String stringFromJNI (); static {System. out. println (System. getProperty ("java. library. path "); System. loadLibrary ("jnicplus5 ");}}

2. Jni-Related Processing2.1 generate related information according to the Java class above. the purpose of the H file is to create a function prototype for the c file to be generated, although not used in the NDK. h file, but it is better to use javah to generate the prototype. Otherwise, java will appear if you accidentally write the standard. lang. unsatisfiedLinkError: Native method not found class error.

D: \ AppWork \ XExample \ workspace \ jnidemo5 \ src> javah com. xcl. jnidemo5.MainActivityD: \ AppWork \ XExample \ workspace \ jnidemo5 \ src> the volume in the dir drive D is the Data volume serial number is 0EC2-012C D: \ AppWork \ XExample \ workspace \ jnidemo5 \ src directory <DIR>. <DIR> .. <DIR> com2014/03/29 529 com_xcl_jnidemo5_MainActivity.h 1 file 529 bytes 3 directories 18,683,146,240 available bytes

2.2. Right-click the directory for jni storage in the Eclipse Android project, select Source Folder, and create jni directory. 2.3 create the c file jnicplus5.c corresponding to the. h file.

/*** Demonstrate the C Implementation of NDK Development * JNI * author: xcl * date: 2014-3-20 */# include <string. h> # include <jni. h>/** Class: com_xcl_jnidemo5_MainActivity * Method: stringFromJNI * Signature: () Ljava/lang/String; */JNIEXPORT jstring JNICALL trim (JNIEnv * env, jobject jobj) {return (* env)-> NewStringUTF (env, "Hello from JNI! ");}

2.4 generate the compilation file Android. mk:

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_MODULE := jnicplus5LOCAL_SRC_FILES := jnicplus5.cinclude $(BUILD_SHARED_LIBRARY)

The LOCAL_MODULE in Android. mk specifies the name of the dynamic library to be generated, which must be consistent with the one specified in Java code. LOCAL_SRC_FILES: you only need to specify the c file of the native function implemented by the Java file. Other files are automatically derived during NDK compilation. LOCAL_PATH indicates finding the source file from the project directory. Other parameters are easy to understand, and they are like handwritten Makefile files. Only. mk has some custom macro definitions.
Application. mk

APP_ABI := all

Application. mk is used to specify the platforms on which to generate the. so file.
2.5 It is easy to compile the. c file into the dynamic library NDK to compile the dynamic library. Go to the jni directory of the Android project and call the NDK-build under the ndk.

D:\AppWork\XExample\workspace\jnidemo5\jni>C:\Ndk\ndk\ndk-build[armeabi-v7a] Compile thumb : jnicplus5 <= jnicplus5.c[armeabi-v7a] SharedLibrary : libjnicplus5.so[armeabi-v7a] Install : libjnicplus5.so => libs/armeabi-v7a/libjnicplus5.so[armeabi] Compile thumb : jnicplus5 <= jnicplus5.c[armeabi] SharedLibrary : libjnicplus5.so[armeabi] Install : libjnicplus5.so => libs/armeabi/libjnicplus5.so[x86] Compile : jnicplus5 <= jnicplus5.c[x86] SharedLibrary : libjnicplus5.so[x86] Install : libjnicplus5.so => libs/x86/libjnicplus5.so[mips] Compile : jnicplus5 <= jnicplus5.c[mips] SharedLibrary : libjnicplus5.so[mips] Install : libjnicplus5.so => libs/mips/libjnicplus5.so

If the content of Application. mk is defined as APP_ABI: = armeabi, only the arm dynamic library is generated.

D:\AppWork\XExample\workspace\jnidemo5\jni>C:\Ndk\ndk\ndk-build[armeabi] Compile thumb  : jnicplus5 <= jnicplus5.c[armeabi] SharedLibrary  : libjnicplus5.so[armeabi] Install        : libjnicplus5.so => libs/armeabi/libjnicplus5.so

3. Run the entire Android project to get the desired result.
MAIL: xcl_168@aliyun.comBLOG: http://blog.csdn.net/xcl168