JNI- java.lang.UnsatisfiedLinkError:找不到本机方法

Question

我正在使用OpenCV开发一个Android项目.有些方法没有Java版本,所以我必须使用NDK在我的项目中使用它们.

这是我第一次使用NDK,所以在搜索了一些例子之后,我编写了我的代码,在我的设备上运行它,并收到以下错误消息:

07-04 10:26:19.555  21270-21270/com.example.MyTest E/AndroidRuntime? FATAL EXCEPTION: main
    java.lang.UnsatisfiedLinkError: Native method not found: com.example.MyTest.JNIlib.readImg:()I
            at com.example.MyTest.JNIlib.readImg(Native Method)
            at com.example.MyTest.MyActivity$2.onClick(MyActivity.java:60)
            at android.view.View.performClick(View.java:4211)
            at android.view.View$PerformClick.run(View.java:17267)
            at android.os.Handler.handleCallback(Handler.java:615)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4898)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773)
            at dalvik.system.NativeStart.main(Native Method)

我多次重新生成.so文件,并检查jni函数的命名.我还为jni函数添加了'extern"C"'包装器.但这些解决方案都没有奏效.

注意:我总是使用Intellij Idea来开发JAVA程序,因为Idea不支持NDK,我必须使用Eclipse来访问NDK,所以...这也是我第一次使用Eclipse.我本可以犯很多愚蠢的错误.大声笑

下面是我的c ++代码和makefile.

LocalMain.cpp

#include <stdio.h>
#include <iostream>
#include <opencv2/nonfree/nonfree.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/nonfree/features2d.hpp>

#include <opencv2/opencv.hpp>  
#include <jni.h>
#include <android/log.h>
#include "LocalFeature.h"
using namespace cv;  
using namespace std;  



int readImg()
{  
    /* do something*/

    return 0;  
}  


// JNI interface functions, be careful about the naming.
extern "C"
{
    JNIEXPORT jint JNICALL Java_com_example_MyTest_JNIlib_readImg(JNIEnv * env, jobject obj);
};

JNIEXPORT jint JNICALL Java_com_example_MyTest_JNIlib_readImg(JNIEnv * env, jobject obj)
{
    return (jint)readImg();
}

LocalFeatures.h和LocalFeatures.cpp没有显示,但我确定问题不在于它们.

Android.mk

LOCAL_PATH:= $(call my-dir)

include $(CLEAR_VARS)
LOCAL_MODULE    := nonfree_prebuilt
LOCAL_SRC_FILES := libnonfree.so
include $(PREBUILT_SHARED_LIBRARY)

include $(CLEAR_VARS)
LOCAL_MODULE    := opencv_java_prebuilt
LOCAL_SRC_FILES := libopencv_java.so
include $(PREBUILT_SHARED_LIBRARY)

include $(CLEAR_VARS)
# Modify LOCAL_C_INCLUDES with your path to OpenCV for Android.
LOCAL_C_INCLUDES:= E:/Java/libs/OpenCV-2.4.9-android-sdk/sdk/native/jni/include
LOCAL_MODULE    := mytest_lib
LOCAL_CFLAGS    := -Werror -O3 -ffast-math
LOCAL_LDLIBS    += -llog -ldl 
LOCAL_SHARED_LIBRARIES := nonfree_prebuilt opencv_java_prebuilt
LOCAL_SRC_FILES := LocalMain.cpp \
LocalFeature.h \
LocalFeature.cpp

include $(BUILD_SHARED_LIBRARY)

那些.cpp文件和.mk文件位于Eclipse项目中.libmytest_lib.so,libopencv_java.so,libnonfree.so可以正确生成.以下.java文件位于Intellij Idea项目中.我已将这些.so文件复制到Idea项目中的\ lib.

JNIlib.java

public class JNIlib {
    static
    {
        try
        {
            // Load necessary libraries.
            System.loadLibrary("opencv_java");
            System.loadLibrary("nonfree");
            System.loadLibrary("mytest_lib");
        }
        catch( UnsatisfiedLinkError e )
        {
            System.err.println("Native code library error.\n");
        }
    }
    public static native int readImg();
}

MainActivity.java的一部分

public class MyActivity extends Activity implements CameraBridgeViewBase.CvCameraViewListener2{

    public View.OnClickListener onClickListener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            JNIlib.readImg();
        }
    };

    /*Other irrevelant code*/
}

非常感谢!

Answer 1

按照JonesV的建议,我从代码中删除了静态.但在那之后,问题仍然存在.

最后我调试了我的程序,当运行到这一行时:

System.loadLibrary("opencv_java");

该程序引发了错误,而不是像我想象的那样正常运行.真正愚蠢的错误:<

现在我发现了一个我以前从未注意到的错误.

java.lang.UnsatisfiedLinkError: Couldn't load opencv_java: findLibrary returned null

这意味着,没有负载.所以我检查了我的项目结构,发现我把我的.so文件放在libs /文件夹中,而不是libs/armeabi /文件夹.

解决方案在这里找到: Android NDK java.lang.UnsatisfiedLinkError:findLibrary返回null

Answer 2

I added

extern "C"

before functions declare ex:

extern "C"
jstring
Java_lara_myapplication_MainActivity_stringFromJNI(
        JNIEnv *env,
    jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

then the error was gone