在Android中使用jni：UNsatisfiedLinkError

Question

我对jni是新手，我正在阅读一个教程来实现一个简单的本机方法，但我得到了一个不满意的LinkError。据我所知，我完全按照教程中的步骤进行了操作。请帮帮我.

下面是java包装器代码：

package com.cookbook.jni;

public class SquaredWrapper {

    // Declare native method (and make it public to expose it directly)
    public static native int squared(int base);

   // Provide additional functionality, that "extends" the native method
   public static int to4(int base)
   {
      int sq = squared(base);
      return squared(sq);
   }

   // Load library
   static {
      System.loadLibrary("squared");
   }
}

下面是我的Android.mk文件的样子：

#include "squared.h"
#include <jni.h>

JNIEXPORT jint JNICALL Java_org_edwards_1research_demo_jni_SquaredWrapper_squared
  (JNIEnv * je, jclass jc, jint base)
{
     return (base*base);
}

下面是我的。h文件的样子：

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

#ifndef _Included_com_cookbook_jni_SquaredWrapper
#define _Included_com_cookbook_jni_SquaredWrapper
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class:     com_cookbook_jni_SquaredWrapper
* Method:    squared
* Signature: (I)I
*/
JNIEXPORT jint JNICALL Java_com_cookbook_jni_SquaredWrapper_squared
  (JNIEnv *, jclass, jint);

#ifdef __cplusplus
}
#endif
#endif

Answer 1

你的JNI签名不匹配。在。c文件中，更改：

JNIEXPORT jint JNICALL Java_org_edwards_1research_demo_jni_SquaredWrapper_squared

到

JNIEXPORT jint JNICALL Java_com_cookbook_jni_SquaredWrapper_squared

通常有两种方法可以通过JNI将本机C“粘合”到Java函数上。第一个是您在这里试图做的，即使用一个预先确定的签名，JNI将识别该签名并将其与适当的Java代码相关联。第二种方法是在包含库时将函数指针、签名和Java类名传递到JNI中。

#include "squared.h"
#include <jni.h>

static const char* SquaredWrapper = "com/cookbook/jni/SquaredWrapper";

jint squared(JNIEnv * env, jobject this, jint base) {
     return (base*base);
}

// Methods to register for SquaredWrapper
static JNINativeMethod SquareWrapperMethods[] = {
        {"squared", "(I)I", squared}
};

jint JNI_OnLoad(JavaVM* vm, void* reserved) {
    JNIEnv* env;
    if ( (*vm)->GetEnv(vm, (void **) &env, JNI_VERSION_1_6) != JNI_OK)
        return JNI_ERR;

    jclass class = (*env)->FindClass(env, SquaredWrapper);
    (*env)->RegisterNatives(env, class, SquaredWrapperMethods, sizeof(SquaredWrapperMethods)/sizeof(SquaredWrapperMethods[0]));

    return JNI_VERSION_1_6;
}

void JNI_OnUnload(JavaVM* vm, void* reserved) {
    JNIEnv* env;
    if ((*vm)->GetEnv(vm, (void**) &env, JNI_VERSION_1_6) != JNI_OK)
        return;

    jclass class = (*env)->FindClass(env, SquaredWrapper);
    (*env)->UnregisterNatives(env, class);

    return;

}