Question

我正在创建一个通过串口发送数据的应用。这需要从本机库调用methos 我有两个本地方法“打开”“关闭”我使用ndk为.so库生成并将它们放在jnilibs文件夹中但仍然会出现错误，说“无法解析相应的jni函数”

SerialPort.c

#include <termios.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <jni.h>

#include "android/log.h"
static const char *TAG="serial_port";
#define LOGI(fmt, args...) __android_log_print(ANDROID_LOG_INFO,  TAG, fmt, ##args)
#define LOGD(fmt, args...) __android_log_print(ANDROID_LOG_DEBUG, TAG, fmt, ##args)
#define LOGE(fmt, args...) __android_log_print(ANDROID_LOG_ERROR, TAG, fmt, ##args)

static speed_t getBaudrate(jint baudrate)
{
    switch(baudrate) {
    case 0: return B0;
    case 50: return B50;
    case 75: return B75;
    case 110: return B110;
    case 134: return B134;
    case 150: return B150;
    case 200: return B200;
    case 300: return B300;
    case 600: return B600;
    case 1200: return B1200;
    case 1800: return B1800;
    case 2400: return B2400;
    case 4800: return B4800;
    case 9600: return B9600;
    case 19200: return B19200;
    case 38400: return B38400;
    case 57600: return B57600;
    case 115200: return B115200;
    case 230400: return B230400;
    case 460800: return B460800;
    case 500000: return B500000;
    case 576000: return B576000;
    case 921600: return B921600;
    case 1000000: return B1000000;
    case 1152000: return B1152000;
    case 1500000: return B1500000;
    case 2000000: return B2000000;
    case 2500000: return B2500000;
    case 3000000: return B3000000;
    case 3500000: return B3500000;
    case 4000000: return B4000000;
    default: return -1;
    }
}

JNIEXPORT jobject JNICALL Java_com_example_richyrony_serial485_SerialPort_open(JNIEnv *env, jobject thiz, jstring path, jint baudrate)
{
    int fd;
    speed_t speed;
    jobject mFileDescriptor;

    /* Check arguments */
    {
        speed = getBaudrate(baudrate);
        if (speed == -1) {
            /* TODO: throw an exception */
            LOGE("Invalid baudrate");
            return NULL;
        }
    }

    /* Opening device */
    {
        jboolean iscopy;
        const char *path_utf = (*env)->GetStringUTFChars(env, path, &iscopy);
        LOGD("Opening serial port %s", path_utf);
        LOGD(" serial port buadrate %s", speed);
//      fd = open(path_utf, O_RDWR | O_DIRECT | O_SYNC);
        fd = open(path_utf,O_RDWR | O_SYNC);               //2011.8.26 
        LOGD("open() fd = %d", fd);
        (*env)->ReleaseStringUTFChars(env, path, path_utf);
        if (fd == -1)
        {
            /* Throw an exception */
            LOGE("Cannot open port");
            /* TODO: throw an exception */
            return NULL;
        }
    }

    /* Configure device */
    {
        struct termios cfg;
        LOGD("Configuring serial port");
        if (tcgetattr(fd, &cfg))
        {
            LOGE("tcgetattr() failed");
            close(fd);
            /* TODO: throw an exception */
            return NULL;
        }

        cfmakeraw(&cfg);
        cfsetispeed(&cfg, speed);
        cfsetospeed(&cfg, speed);

        if (tcsetattr(fd, TCSANOW, &cfg))
        {
            LOGE("tcsetattr() failed");
            close(fd);
            /* TODO: throw an exception */
            return NULL;
        }
    }

    /* Create a corresponding file descriptor */
    {
        jclass cFileDescriptor = (*env)->FindClass(env, "java/io/FileDescriptor");
        jmethodID iFileDescriptor = (*env)->GetMethodID(env, cFileDescriptor, "<init>", "()V");
        jfieldID descriptorID = (*env)->GetFieldID(env, cFileDescriptor, "descriptor", "I");
        mFileDescriptor = (*env)->NewObject(env, cFileDescriptor, iFileDescriptor);
        (*env)->SetIntField(env, mFileDescriptor, descriptorID, (jint)fd);
    }

    return mFileDescriptor;
}

void  Java_com_example_richyrony_serial485_SerialPort_close
  (JNIEnv *env, jobject thiz)
{
    jclass SerialPortClass = (*env)->GetObjectClass(env, thiz);
    jclass FileDescriptorClass = (*env)->FindClass(env, "java/io/FileDescriptor");

    jfieldID mFdID = (*env)->GetFieldID(env, SerialPortClass, "mFd", "Ljava/io/FileDescriptor;");
    jfieldID descriptorID = (*env)->GetFieldID(env, FileDescriptorClass, "descriptor", "I");

    jobject mFd = (*env)->GetObjectField(env, thiz, mFdID);
    jint descriptor = (*env)->GetIntField(env, mFd, descriptorID);

    LOGD("close(fd = %d)", descriptor);
    close(descriptor);
}

SerialPort.Java

package com.example.richyrony.serial485;


import java.io.File;
import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import android.util.Log;

public class SerialPort {

    private static final String TAG = "SerialPort";

    /*
     * Do not 

remove or rename the field mFd: it is used by native method close();
     */
    private FileDescriptor mFd;
    private FileInputStream mFileInputStream;
    private FileOutputStream mFileOutputStream;
public SerialPort(File device, int baudrate) throws SecurityException, IOException {

    /* Check access permission */
    if (!device.canRead() || !device.canWrite()) {
        try {

            if (!device.canRead() || !device.canWrite()) {
                throw new SecurityException();
            } 
        }catch (Exception e) {
                e.printStackTrace();
                throw new SecurityException();
        }
    }



    mFd = open(device.getAbsolutePath(), baudrate);
    if (mFd == null) {
        Log.e(TAG, "native open returns null");
        throw new IOException();
    }
    mFileInputStream = new FileInputStream(mFd);
    mFileOutputStream = new FileOutputStream(mFd);
}

// Getters and setters
public InputStream getInputStream() {
    return mFileInputStream;
}

public OutputStream getOutputStream() {
    return mFileOutputStream;
}

// JNI
static {
    System.loadLibrary("serial_port");

}

private native static FileDescriptor open(String path, int baudrate);
public native void close();

}

这些是我的java类和本机文件。请帮忙

Answer 1

正如我解释elsewhere，不要期望Android Studio神奇地将本机方法声明解析为预构建的库（即使它被正确复制到 src / main / jnLibs ）。

您可以忽略此错误消息：您的APK仍将安装预构建的库，并且本机方法将在运行时解析。

您可以为这些方法或整个班级添加@SuppressWarnings("JniMissingFunction") private native static FileDescriptor open(String path, int baudrate); @SuppressWarnings("JniMissingFunction") public native void close();注释：

private SerialPort m_serialPort = new SerialPort();

如果您可以在任何设备上，甚至在模拟器上安装APK，并且加载了 SerialPort 类，那么您的JNI包装器配置正确。当系统无法加载本机库时，它会将有用的错误消息写入 logcat 。

让我对＆＃34; SerialPort 类进行扩展＆＃34; 。在Java中，类加载器可能（更确切地说应该＆＃39;）推迟加载类，直到确实需要为止。因此，只需在APK中使用类就不会触发其静态构造函数。但是如果你有一个领域

public SerialPort() {}

在您的MainActivity中

，然后将加载该类，即使您实际上没有触及此 m_serialPort ，也会初始化JNI。请注意，我向 SerialPort 类添加了一个无操作的默认构造函数：

          Date     Open     High      Low    Close
1 Nov 28, 2017 0.233394 0.234871 0.223832 0.225542 
2 Nov 27, 2017 0.225910 0.234219 0.212298 0.233113
3 Nov 26, 2017 0.229367 0.235126 0.215153 0.226367
4 Nov 25, 2017 0.234212 0.239257 0.223383 0.228617
5 Nov 24, 2017 0.215836 0.236280 0.209834 0.234195
6 Nov 23, 2017 0.228887 0.232974 0.214334 0.216585

这不会测试JNI代码本身，比如转换参数等。如果您没有可用于测试代码的真实设备，则应设计一些模拟接口，这些接口将扮演实际串行端口的角色。

无法解决相应的jni功能

1 个答案: