java - 在android中使用JNI对 'multiply'的 undefined reference

Question

我是 android JNI 的新手，正在尝试以下代码:

包名称: com.example.jnitest

Java 类:

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    MainActivity mainActivity = new MainActivity();


    System.out.println("Sum of two variables : "+ sumOfTwovariable((int)mainActivity.multiply(10, 25), 10));
}

public native long sumOfTwovariable(int v1, int v2);

static {
    System.loadLibrary("JNITest");
}

public native long multiply(int v1, int v2);
static{
    System.loadLibrary("com_example_pdemo_MainActivity");
}

}

<小时/>

Android.mk 文件

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_MODULE    := JNITest
LOCAL_SRC_FILES := JNITest.cpp
LOCAL_SHARED_LIBRARIES := Prebuild_com_example_pdemo_MainActivity
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/includes
LOCAL_STATIC_LIBRARIES := Prebuild_com_example_pdemo_MainActivity
include $(BUILD_SHARED_LIBRARY)


include $(CLEAR_VARS)
LOCAL_MODULE    := Prebuild_com_example_pdemo_MainActivity
LOCAL_SRC_FILES :=    $(TARGET_ARCH_ABI)/libcom_example_pdemo_MainActivity.so

include $(PREBUILT_SHARED_LIBRARY)

我已将预构建的 com_example_pdemo_MainActivity.so lib 放置在 JNI->armeabi(写入多个函数)文件夹中，包含在 Android.mk 文件中

<小时/>

JNI 内部:

使用以下命令创建头文件:javah -jni -classpath....

Header file created using javah : com_example_jnitest_MainActivity.h

  /* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_example_jnitest_MainActivity */

#ifndef _Included_com_example_jnitest_MainActivity
#define _Included_com_example_jnitest_MainActivity
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_example_jnitest_MainActivity
  * Method:    sumOfTwovariable
  * Signature: (II)J
*/
JNIEXPORT jlong JNICALL    Java_com_example_jnitest_MainActivity_sumOfTwovariable(JNIEnv *, jobject, jint, jint);

 #ifdef __cplusplus
 }
#endif

#endif

原生函数的定义:JNITest.cpp

  #include "com_example_jnitest_MainActivity.h"

extern "C" {
long multiply(int val1,int val2);
}

   JNIEXPORT jlong JNICALL      Java_com_example_jnitest_MainActivity_sumOfTwovariable(
    JNIEnv *env, jobject obj, jint val1, jint val2) {
int val=multiply(val1,val2);
return (val+val1);

}

当我编译它时，我得到了对“乘法”的 undefined reference 。让我知道我犯了什么错误。

提前致谢..

Answer 1

multiply 也是 native 方法。它的定义应与 sumOfTwovariable 相同:

JNIEXPORT jlong JNICALL    Java_com_example_jnitest_MainActivity_multiply(JNIEnv *, jobject, jint, jint);