串口通信Android设备通过串口与其他设备进行通信的一种方式，对于Android串口操作基本上就是对应串口文件的读写，基本思路就是：
1.对串口文件进行配置（波特率等），打开串口文件2.读写串口
3.关闭串口文件
但是这里需要注意的是Android中读写串口需要用到FileDescriptor类(文件描述符)
关于串口通信，Google已经给出了源码，具体地址如下：https://github.com/cepr/android-serialport-api，大家可以自行下载使用，直接使用时因为他已经将so已经打包生成好了，所以要保留Google原本的包名才行，如果不保留Google原本的包名你将.so放在你的项目中你会发现是不能使用的，原因是因为so中的方法名是通过开源项目的包名+方法名来的。放在你项目中包名都变了，所以so文件将无法找到对应的方法的，用Google原本so项目结构如下，注意加载so文件的SerialPort.java类一定要位于Google原本的包名android_serialport_api下面
为了项目包名的一致性，不想用Google的包名，全部用自己的包名，这个时候就要自己生成so文件了，下面讲解怎么自己生成so文件。首先在Android Studio新建一个支持C/C++的项目
注意要勾选红框中的内容，新建好的工程：会帮我们新建好两个文件，native-lib.cpp 和CMakeLists.txt
将下载的Google源码包中的SerialPort.java 类，添加到项目中
import android.util.Log;
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;
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, int flags) throws SecurityException, IOException {
/* Check access permission */
if (!device.canRead() || !device.canWrite()) {
try {
/* Missing read/write permission, trying to chmod the file */
Process su;
su = Runtime.getRuntime().exec("/system/bin/su");
String cmd = "chmod 666 " + device.getAbsolutePath() + "\n"
+ "exit\n";
su.getOutputStream().write(cmd.getBytes());
if ((su.waitFor() != 0) || !device.canRead()
|| !device.canWrite()) {
throw new SecurityException();
}
} catch (Exception e) {
e.printStackTrace();
throw new SecurityException();
}
}
mFd = open(device.getAbsolutePath(), baudrate, flags);
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
private native static FileDescriptor open(String path, int baudrate, int flags);
public native void close();
static {
System.loadLibrary("twaer_control");
}
}
修改最后一部分
static {
System.loadLibrary("twaer_control");
}
"twaer_control"是自定义的要生成的so文件名，记住这个名，后面要用到
此时项目结构如下：
下面一步就是要生成 C语言头文件
打开 Terminal（View -> Tool Windows -> Terminal）
输入cd app\src\main\java进入源码所在目录
输入javah com.test.myapplication.SerialPort生成头文件
将前面生成的 .h 文件移入cpp文件夹中，右键cpp菜单中选择New -> C/C++ Source File创建与 .h 文件同名的 .c 文件
将下载的Google源码包中的SerialPort.c 类拷贝到com_test_myapplication_SerialPort.c中
/*
* Copyright 2009-2011 Cedric Priscal
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <termios.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <jni.h>
#include "SerialPort.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;
}
}
/*
* Class: android_serialport_SerialPort
* Method: open
* Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor;
*/
JNIEXPORT jobject JNICALL Java_android_1serialport_1api_SerialPort_open
(JNIEnv *env, jclass thiz, jstring path, jint baudrate, jint flags)
{
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 with flags 0x%x", path_utf, O_RDWR | flags);
fd = open(path_utf, O_RDWR | flags);
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);
//设置波特率
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;
}
/*
* Class: cedric_serial_SerialPort
* Method: close
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_android_1serialport_1api_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);
}
删除红色部分报错的问题，点击右上角的Sync Now，成功之后下一步就要要配置NDK,生成so文件，这里用到的是CMakeLists.txt
主要就是讲红色框中的内容修改为我们上面的c文件名称，其中1、3都是上面SerialPort.java中设置的生成so文件名，1和3两个ya保持一致，2是上面的c文件。接下来再看下build.gradle的配置改变：
apply plugin: 'com.android.application'
android {
compileSdkVersion 27
defaultConfig {
applicationId "com.test.myapplication"
minSdkVersion 18
targetSdkVersion 27
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
externalNativeBuild {
cmake {
cppFlags ""
}
}
ndk {
abiFilters 'armeabi', 'armeabi-v7a', "x86", "x86_64", "arm64-v8a"
}
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
externalNativeBuild {
cmake {
path "CMakeLists.txt"
}
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:27.1.1'
implementation 'com.android.support.constraint:constraint-layout:1.1.0'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}
主要多了两个地方的改变：
1：defaultConfig中添加：
externalNativeBuild {
cmake {
cppFlags ""
}
}
2：在android{}中添加：
externalNativeBuild {
cmake {
path "CMakeLists.txt"
}
}
3：配置so文件生成平台
ndk {
abiFilters 'armeabi', 'armeabi-v7a', "x86", "x86_64", "arm64-v8a"
}
点击右上角的Sync Now，成功后我们可以在app\build\intermediates\cmake\debug\obj目录下看到生成了我们之前设置的平台目录，但里面还没有so文件。
到这里就基本可以over了，最后我们点击Build--->Make Project，成功之后我们会在app\build\intermediates\cmake\debug\obj各个平台目录下看到已经生成了so文件。
