Android 开发中 JAVA 调用 C++

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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

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packageorg.apache;
 
importAndroid.util.Log;
 
publicclass 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");
        }
    }
 
    publicstatic native long add(longa, longb);
}

2. [代码]下面片断给出主activity中如何调用这个类/方法

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publicvoid 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");
      longsum = 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

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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

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/* 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”

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#include "org_apache_NativeAdd.h"
 
JNIEXPORT jlong JNICALL Java_org_apache_NativeAdd_add
  (JNIEnv *env, jclass c, jlong a, jlong b)
{
    returna + 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.

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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.

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adb push native/libNativeAdd.so/system/lib
adbinstallbin/CallNative.apk

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