[Google Android] understands NDK (1)--compiling Android. so files

Original address: http://www.cnblogs.com/tamer/archive/2011/01/18/1938307.html

To be blunt, C code is made into a dynamic library, called by Java Code (JNI). The executable program that can run directly on Android is not written in C.

NDK development requires a cross-compilation environment that requires the installation of the Cygwin, NDK.

These preparations do not say a lot of online, of course, can also ask me.

Tell me about the. so file generation

--------------------------------------------------------------------------------------------------------------- -----------------------------------

compiling Android. so file

1. Defining the Native Interface

Create an Android project "Ndk_plus" and add a JNI class.

Figure 1:android's SDK Project

Jni.java Code:

Package kun.ndk.plus;
public class JNI {
public native int plus (int a, int b);
}

2. Generate the corresponding. h file according to the Jni.java file

CMD to the bin directory of the Ndk_plus project, and then execute javah–classpath. –jni Kun.ndk.plus.JNI

This will generate the Kun_ndk_plus_jni.h header file. The contents are as follows:

/* Don't EDIT this file-it are machine generated */
#include <jni.h>
/* Header for class KUN_NDK_PLUS_JNI */

#ifndef _included_kun_ndk_plus_jni
#define _included_kun_ndk_plus_jni
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class:kun_ndk_plus_jni
* Method:plus
* Signature: (II) I
*/
Jniexport Jint Jnicall Java_kun_ndk_plus_jni_plus
(JNIEnv *, Jobject, Jint, Jint);

#ifdef __cplusplus
}
#endif
#endif

If prompted without the Javah command, you will need to locate the directory where Javah.exe is located (C:\Program files\java\jdk1.5.0\bin) and add this directory to the environment variable path.

3. Implement the corresponding. c file according to the. h file

Create a kun_ndk_plus_jni.c file in eclipse (all other editing tools are available)

//-------------------------------------------------------------------------------------------------------------

#include <jni.h>

#include "kun_ndk_plus_jni.h"

Jniexport Jint Jnicall Java_kun_ndk_plus_jni_plus

(JNIEnv *e, Jobject J, Jint A, jint b)

{

return a + B;

}

//-------------------------------------------------------------------------------------------------------------

Note the red part. Because the function declaration in the generated. h does not have a formal parameter, you need to add the parameter variable yourself when you implement it.

Also note that you want to add a carriage return (the characteristics of the GCC compiler) after the blue curly braces.

4. Making the. mk File

Create a TXT file under this folder by creating a new plus folder under the Apps directory in the NDK directory.

Enter the content:

App_project_path: = $ (call My-dir)

App_modules: = Plus

Rename to Application.mk

In the Ndk/sources/samples directory, create a new plus folder under this folder, creating a TXT file, and enter the following:

Local_path: = $ (call My-dir)

Include $ (clear_vars)

Local_module: = Plus

Local_src_files: = Kun_ndk_plus_jni.c

Include $ (build_shared_library)

Rename the name Android.mk. Copy the. c and. h files to this folder.

Keywords specific meaning see Doc/overview. Txt

5. Compiling

Launch Cygwin, CD to NDK directory

Make App=plus

After success, there will be a libplus.so file under Apps/plus/libs/armeabi.

6. The following is the use of the. so file in the Java code to add to Android engineering.

[Google Android] understands NDK (1)--compiling Android. So file