最近因为需要在Android平台进行电子秤的开发，首先第一步就是需要解决Android串口通信获取电子秤的称重信息。
google官方给我们提供了现成的解决方案，里面有编译好的apk文件还有源代码可以直接参考使用。地址：http://code.google.com/p/android-serialport-api/。
但是上面的地址国内屏蔽了。如果不方便访问，也可以在国内的gitee等开源社区找到fock的项目进行下载，或者是通过百度搜索google android-serialport-api找到。
拿到工业用的电子秤等设备的第一步，就是要熟悉一下它的通信协议。一般这些设备都会提供类似RS232或者module bus等串口通信协议，不同的厂家不同的设备串口协议不同，需要联系厂家，仔细阅读各类设备的通信协议。熟悉通信协议之后，可以结合一些串口调试工具进行调试，测试通过之后就可以写代码实现功能了。
下面就直接演示在Android当中，串口通信的用法步骤：
1. 加载编译好的so包
完全可以下载c源码，自行编译产生so包。但是直接引用编译好的so包能节约大量的时间，这个可以直接搜索下载。
需要说明的是，要先注意查看一下目标设备的Android平台，可以通过adb shell登录后输入一下命令查看：
adb shell getprop ro.product.cpu.abi
这条命令会返回设备的主架构，例如 arm64-v8a、armeabi-v7a、x86 等等。我们的so包就应该与之对应。
如下：
2. 准备Android串口通信的助手类
google的示范项目中有现成的源代码，可以直接复制到项目中使用。
要注意的是项目中，要建立与google项目中一样的包名 android_serialport_api，否则会报错找不到类。
SerialPort ：
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 setterspublic InputStream getInputStream() {return mFileInputStream;}public OutputStream getOutputStream() {return mFileOutputStream;}/**************************************modify start********************************************/public void closeStream() {try {if (null != mFileOutputStream) {mFileOutputStream.close();mFileOutputStream = null;}if (null != mFileInputStream) {mFileInputStream.close();mFileInputStream = null;}} catch (Exception e) {e.printStackTrace();}}/**************************************modify end********************************************/// JNIprivate native static FileDescriptor open(String path, int baudrate, int flags);public native void close();static {System.loadLibrary("serial_port");}}
SerialPortFinder ：
public class SerialPortFinder {public class Driver {public Driver(String name, String root) {mDriverName = name;mDeviceRoot = root;}private String mDriverName;private String mDeviceRoot;Vector<File> mDevices = null;public Vector<File> getDevices() {if (mDevices == null) {mDevices = new Vector<File>();File dev = new File("/dev");File[] files = dev.listFiles();int i;for (i=0; i<files.length; i++) {if (files[i].getAbsolutePath().startsWith(mDeviceRoot)) {Log.d(TAG, "Found new device: " + files[i]);mDevices.add(files[i]);}}}return mDevices;}public String getName() {return mDriverName;}}private static final String TAG = "SerialPort";private Vector<Driver> mDrivers = null;Vector<Driver> getDrivers() throws IOException {if (mDrivers == null) {mDrivers = new Vector<Driver>();LineNumberReader r = new LineNumberReader(new FileReader("/proc/tty/drivers"));String l;while((l = r.readLine()) != null) {// Issue 3:// Since driver name may contain spaces, we do not extract driver name with split()String drivername = l.substring(0, 0x15).trim();String[] w = l.split(" +");if ((w.length >= 5) && (w[w.length-1].equals("serial"))) {Log.d(TAG, "Found new driver " + drivername + " on " + w[w.length-4]);mDrivers.add(new Driver(drivername, w[w.length-4]));}}r.close();}return mDrivers;}public String[] getAllDevices() {Vector<String> devices = new Vector<String>();// Parse each driverIterator<Driver> itdriv;try {itdriv = getDrivers().iterator();while(itdriv.hasNext()) {Driver driver = itdriv.next();Iterator<File> itdev = driver.getDevices().iterator();while(itdev.hasNext()) {String device = itdev.next().getName();String value = String.format("%s (%s)", device, driver.getName());devices.add(value);}}} catch (IOException e) {e.printStackTrace();}return devices.toArray(new String[devices.size()]);}public String[] getAllDevicesPath() {Vector<String> devices = new Vector<String>();// Parse each driverIterator<Driver> itdriv;try {itdriv = getDrivers().iterator();while(itdriv.hasNext()) {Driver driver = itdriv.next();Iterator<File> itdev = driver.getDevices().iterator();while(itdev.hasNext()) {String device = itdev.next().getAbsolutePath();devices.add(device);}}} catch (IOException e) {e.printStackTrace();}return devices.toArray(new String[devices.size()]);}
}
3. 项目中进行串口通信的开发
主要示例代码如下：
- 发送串口
private void sendData(String data) {try {// 打开串口mSerialPort = new SerialPort(new File("/dev/ttyS3"),9600, // 波特率// 校验位（0=NONE）0);mOutputStream = mSerialPort.getOutputStream();} catch (SecurityException | IOException e) {e.printStackTrace();}if (mOutputStream != null) {try {// 将字符串转换为字节数组并发送mOutputStream.write(data.getBytes());mInputStream = mSerialPort.getInputStream();new ReadThread().start();} catch (IOException e) {e.printStackTrace();}}}
- 线程操作
private class ReadThread extends Thread {@Overridepublic void run() {super.run();while (!isInterrupted()) {int size;try {byte[] buffer = new byte[64];if (mInputStream == null) return;size = mInputStream.read(buffer);if (size > 0) {onDataReceived(buffer, size);}} catch (IOException e) {e.printStackTrace();return;}}}}
- UI回显
void onDataReceived(final byte[] buffer, final int size) {runOnUiThread(new Runnable() {@Overridepublic void run() {String msg = new String(buffer, 0, buffer.length);Log.i("gw", msg);mTextView.append(msg);// //断开串口连接
// mSerialPort.close();}});}
