Android 开发中 JAVA 调用 C++

http://www.oschina.net/code/snippet_4873_3279#4874

代码片段(7)[全屏查看所有代码]

1. [代码]步骤 #1:使用ANT编译项目 NativeAdd.java     

package org.apache;

import Android.util.Log;

public class NativeAdd {
    static {
        try {
            Log.i( "JNI" , "Trying to load libNativeAdd.so" );
            System.loadLibrary( "NativeAdd" );
        }
        catch (UnsatisfiedLinkError ule) {
            Log.e( "JNI" , "WARNING: Could not load libNativeAdd.so" );
        }
    }

    public static native long add( long a, long b);
}

2. [代码]下面片断给出主activity中如何调用这个类/方法     

public void onClick(View view) {
      Log.i(LOG_TAG, "onClick" );

      EditText a = (EditText) findViewById(R.id.a);
      EditText b = (EditText) findViewById(R.id.b);
      EditText c = (EditText) findViewById(R.id.c);
      Log.i(LOG_TAG, "calling native method" );
      long sum = NativeAdd.add( Long.parseLong(a.getText().toString()),
              Long.parseLong(b.getText().toString()));
      Log.i(LOG_TAG, "back from native method" );
      String text = Long.toString(sum);
      c.setText( "Native add returns = " + text.subSequence( 0 , text.length()));
  }

3. [代码]步骤#2:运行下面的命令产生头文件     

javah -classpath ../../Android.jar;../bin/classes; org.apache.NativeAdd

4. [代码]新产生的头文件“(org_apache_CallNative.h”内容如下     

/* DO NOT EDIT THIS FILE - it is machine generated */
#include
/* Header for class org_apache_NativeAdd */

#ifndef _Included_org_apache_NativeAdd
#define _Included_org_apache_NativeAdd
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     org_apache_NativeAdd
 * Method:    add
 * Signature: (JJ)J
 */
JNIEXPORT jlong JNICALL Java_org_apache_NativeAdd_add
  (JNIEnv *, jclass, jlong, jlong);

#ifdef __cplusplus
}
#endif
#endif

5. [代码]步骤#3: 编写C文件如下“org_apache_NativeAdd.c”     

#include "org_apache_NativeAdd.h"

JNIEXPORT jlong JNICALL Java_org_apache_NativeAdd_add
  (JNIEnv *env, jclass c, jlong a, jlong b)
{
    return a + b;
}

6. [代码]步骤#5: 编译和连接 org_apache_NativeAdd.c/org_apache_NativeAdd.h为一个共享库.     

arm-none-linux-gnueabi- gcc  -I /usr/lib/jvm/java-1 .5.0-sun /include -I /usr/lib/jvm/java-1 .5.0-sun /include/linux  -fpic -c org_apache_NativeAdd.c
arm-none-linux-gnueabi-ld -T armelf_linux_eabi.xsc -shared -o libNativeAdd.so org_apache_NativeAdd.o

7. [代码]步骤 #6: 复制编译文件到模拟器中. 同时安装APK程序.     

adb push native /libNativeAdd .so /system/lib
adb install bin /CallNative .apk