通过手机USB控制外部设备的实例

手机本身就是一台功能强大的计算机，通过其USB接口可以方便地控制外部设备，前提是外部设备也要有USB接口。
本实例用到一个四路USB智能继电器接口模块，价格便宜，网上可以买到，型号是LCUS-4 型四路USB继电器模块智能控制开关，是这个样子。

模块上有单片微控制器、USB转串口控制芯片CH340 、四路继电器和指示灯，细节请参考说明书。

为了使用接口模块，必须在build.gradle中导入厂商提供的驱动库。

dependencies {...api files('libs/CH34xUARTDrive_no_toast.jar')}

权限等设置

获取USB HOST权限

<uses-feature android:name="android.hardware.usb.host" />

USB设备插入时启动相关ACTIVITY或SERVICE

<intent-filter><action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" />
</intent-filter>

USB设备插入时检索需要过滤的设备列表

<meta-data android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" android:resource="@xml/device_filter" />

需要过滤的设备列表

<resource><usb-device product-id="29987" vendor-id="6790" /><usb-device product-id="21795" vendor-id="6790" /><usb-device product-id="21778" vendor-id="6790" />
</resource>

在公共库commlib里有三个类：

MyApp
需要将芯片CH340的驱动类CH34xUARTDriver的对象创建在 Application 类下，以保证在应用有多个Activity 切换时均能进行串口收发。

class MyApp : Application() {lateinit var driver: CH34xUARTDriver
}

Ch34x
这里包括CH34x驱动和相关参数。

class Ch34x(val myApp: MyApp = MyApp(),var isOpen: Boolean = false,var baudRate: Int = 9600,var stopBit: Byte = 1,var dataBit: Byte = 8,var parity: Byte = 0,var flowControl: Byte = 0
) {}

Ch34xAction
这里包括若干操作USB接口的静态方法。

object Ch34xAction {private lateinit var handler: Handlerprivate lateinit var ch34x: Ch34x/*** 注入Ch34x* @param ch34 Ch34x的实例* @return Unit*/fun setCh34x(ch34: Ch34x) {ch34x = ch34}/*** 注入Handler*  @param handler Handler的实例*  @return Unit*/fun setHandler(handler: Handler) {this.handler = handler}/*** 打开设备* @return 执行结果String*/fun open(): String {return with(ch34x) {if (!isOpen) {if (myApp.driver.ResumeUsbPermission() == 0) {//Resume usb device list//ResumeUsbList方法用于枚举CH34X设备以及打开相关设备when (myApp.driver.ResumeUsbList()) {-1 -> {myApp.driver.CloseDevice()"Open failed! ResumeUsbList()=-1"}0 -> {if (myApp.driver.mDeviceConnection != null) {//对串口设备进行初始化操作if (!myApp.driver.UartInit()) {"Initialization failed!"} else {isOpen = true//开启读线程读取串口接收的数据
//                                    startReadThread()readDataCoroutine()"Device opened"}} else {"Open failed! mDeviceConnection is null"}}else -> {"未授权限!"}}} else {"ResumeUsbPermission() != 0"}} else {"no action executed"}}}/*** 关闭设备* @return 执行结果String*/fun close(): String {return with(ch34x) {if (isOpen) {isOpen = false
//                try {
//                    Thread.sleep(200)
//                } catch (e: InterruptedException) {
//                    // TODO Auto-generated catch block
//                    e.printStackTrace()
//                }job.cancel()myApp.driver.CloseDevice()"Device closed"} else {"no action executed"}}}/*** 配置设备参数* @return 执行结果String*/fun config(): String {return with(ch34x) {if (myApp.driver.SetConfig(baudRate, dataBit, stopBit, parity, flowControl)) {"Config successfully"} else {"Config failed!"}}}/*** 数据写入设备* @param outputString 十六进制字符形式的数据* @return 执行结果String*/fun write(outputString: String): String {return with(ch34x.myApp.driver) {val toSend: ByteArray = toByteArray(outputString)if (WriteData(toSend, toSend.size) < 0) {"Write failed!"} else {"Write successfully"}}}/*** 判断设备是否连接* @return 连接状态*/fun isConnected(): Boolean {return ch34x.myApp.driver.isConnected}/*** 启动读数据线程*/private fun startReadThread() {thread {val buffer = ByteArray(4096)while (true) {val msg = Message.obtain()val length: Int = ch34x.myApp.driver.ReadData(buffer, 4096)if (length > 0) {
//                    val inputStr = String(buffer, 0, length)    //以字符串形式输出val inputStr = toHexString(buffer)msg.obj = inputStrif (::handler.isInitialized){handler.sendMessage(msg)}}}}}private val job = Job()     // background job for coroutineprivate val scope = CoroutineScope(job) // coroutine scope/*** 启动读数据协程*/private fun readDataCoroutine() {scope.launch {val buffer = ByteArray(4096)while (true) {val msg = Message.obtain()val length: Int = ch34x.myApp.driver.ReadData(buffer, 4096)if (length > 0) {val inputStr = String(buffer, 0, length)    //以字符串形式输出
//                    val inputStr = toHexString(buffer)msg.obj = inputStrif (::handler.isInitialized){handler.sendMessage(msg)}}}}}/*** 将ByteArray转化为十六进制String* @param bytes     需要转换的byte[]数组* @return 转换后的String*/private fun toHexString(bytes: ByteArray?): String {var result = String()var hexString: Stringbytes?.let {for (bt in it) {hexString = Integer.toHexString((if(bt < 0) bt + 256 else bt).toInt())result += if (hexString.length == 1)  "0$hexString" else "$hexString "}}return result}/*** 将String转化为byte[]数组* @param str 需要转换的String对象* @return 转换后的byte[]数组*/private fun toByteArray(str: String): ByteArray {/* 1.先去除String中的' '，然后将String转换为char数组 */val charArray = str.toCharArray().filterNot { it.isWhitespace()}.toCharArray()val length = charArray.size/* 将char数组中的值转成一个实际的十进制数组 */val evenLength = if (length % 2 == 0) length else length + 1 //如果长度未基数则加一if (evenLength != 0) {val data = IntArray(evenLength)data[evenLength - 1] = 0for (i in 0 until length) {when (val char: Char = charArray[i]) {in '0'..'9' -> {data[i] = char - '0'}in 'a'..'f' -> {data[i] = char - 'a' + 10}in 'A'..'F' -> {data[i] = char - 'A' + 10}}}/* 将每个char的值(十进制)每两个组成一个16进制数据 */val byteArray = ByteArray(evenLength / 2)for (i in 0 until evenLength / 2) {byteArray[i] = (data[i * 2] * 16 + data[i * 2 + 1]).toByte()}return byteArray}return byteArrayOf()}}

需要说明的是上面的读数据线程并没有使用，是个备用方案。这里用协程来读取USB设备的数据。

应用APP

activity

页面LAYOUT
只有一个简单ACTIVITY，通过页面开关经USB控制四个继电器。

class MainActivity : AppCompatActivity() {private lateinit var viewModel: MainViewModelprivate lateinit var handler: Handlerprivate var stateMsg = ""override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)val binding = ActivityMainBinding.inflate(layoutInflater)setContentView(binding.root)//获取ViewModel实例viewModel = ViewModelProvider(this).get(MainViewModel::class.java)//USB权限检查if (viewModel.usbPermissionCheck()) {showMsg("完美支持USB HOST")} else {showMsg("你的手机不支持USB HOST，请换手机")exitProcess(0)}//设备返回信息处理Handler定义handler = object : Handler(Looper.getMainLooper()) {override fun handleMessage(msg: Message) {stateMsg += msg.obj as Stringif (stateMsg.length >= 40) {    //状态信息是分段返回，全部返回后再行处理binding.textView.text = stateMsgbinding.switch1.isChecked = stateMsg[6] == 'N'binding.switch2.isChecked = stateMsg[16] == 'N'binding.switch3.isChecked = stateMsg[26] == 'N'binding.switch4.isChecked = stateMsg[36] == 'N'binding.toggleBtn1.isChecked = stateMsg[6] == 'N'binding.toggleBtn2.isChecked = stateMsg[16] == 'N'binding.toggleBtn3.isChecked = stateMsg[26] == 'N'binding.toggleBtn4.isChecked = stateMsg[36] == 'N'stateMsg = ""}}}//注入HandlerviewModel.setHandler(handler)//toggleBtnOpen Listenerbinding.toggleBtnOpen.setOnCheckedChangeListener { _, isChecked ->val returnMsg: Stringif (isChecked) {returnMsg = viewModel.open()if (returnMsg != "Device opened") {binding.toggleBtnOpen.isChecked = false} else {binding.btnConfig.isEnabled = true}} else {returnMsg = viewModel.close()if (returnMsg != "Device closed") {binding.toggleBtnOpen.isChecked = true} else {binding.btnConfig.isEnabled = falsebinding.btnGetState.isEnabled = falsebinding.toggleBtn1.isEnabled = falsebinding.toggleBtn2.isEnabled = falsebinding.toggleBtn3.isEnabled = falsebinding.toggleBtn4.isEnabled = false}}showMsg(returnMsg)
//            binding.textView.text = returnMsg}//btnConfig Listenerbinding.btnConfig.setOnClickListener {val returnMsg = viewModel.config()if (returnMsg == "Config successfully") {binding.btnGetState.isEnabled = truebinding.toggleBtn1.isEnabled = truebinding.toggleBtn2.isEnabled = truebinding.toggleBtn3.isEnabled = truebinding.toggleBtn4.isEnabled = trueThread.sleep(200)viewModel.requestState()}showMsg(viewModel.config())}//btnGetState Listenerbinding.btnGetState.setOnClickListener {showMsg(viewModel.requestState())}//btnClear Listenerbinding.btnClear.setOnClickListener {binding.textView.text = ""}//set toggleBtn1..4 ListenersetOnCheckedChangeListener(binding.toggleBtn1, 1)setOnCheckedChangeListener(binding.toggleBtn2, 2)setOnCheckedChangeListener(binding.toggleBtn3, 3)setOnCheckedChangeListener(binding.toggleBtn4, 4)}//toggleBtn1..4 Listenerprivate fun setOnCheckedChangeListener(toggleButton: ToggleButton, ToggleButtonId: Int) {toggleButton.setOnCheckedChangeListener { _, isChecked ->showMsg(viewModel.setSwitch(ToggleButtonId, isChecked))Thread.sleep(200)   //给外部设备一些处理时间viewModel.requestState()}}private fun showMsg(msg: String){Toast.makeText(this, msg, Toast.LENGTH_SHORT).show()}}

MainViewModel

对数据的访问和控制都在这里实现。

class MainViewModel : ViewModel() {private val ch34x = Ch34x()init {//注入Ch34xCh34xAction.setCh34x(ch34x)}/*** usb权限检查* @return 是否有usb权限*/fun usbPermissionCheck() : Boolean {ch34x.myApp.driver = CH34xUARTDriver(MyApplication.context.getSystemService(AppCompatActivity.USB_SERVICE)  as UsbManager,MyApplication.context,"cn.wch.wchusbdriver.USB_PERMISSION")return ch34x.myApp.driver.UsbFeatureSupported()}/*** 注入Handler* @param handler Handler实例*/fun setHandler(handler: Handler) {Ch34xAction.setHandler(handler)}/*** 通过向USB输出数据控制继电器的开关* @param switchId 继电器序号* @param isOn 开关状态* @return 执行结果String*/fun setSwitch(switchId: Int, isOn: Boolean) : String {val result = with(StringBuilder()) {append("A0 ")when (switchId) {1 -> {append("01 ")append(if (isOn) "01 A2" else "00 A1")}2 -> {append("02 ")append(if (isOn) "01 A3" else "00 A2")}3 -> {append("03 ")append(if (isOn) "01 A4" else "00 A3")}4 -> {append("04 ")append(if (isOn) "01 A5" else "00 A4")}else -> {}}toString()}return write(result)}/*** 打开设备* @return 执行结果String*/fun open() : String {return try {Ch34xAction.open()} catch (e: Exception) {e.stackTraceToString()}}/*** 关闭设备* @return 执行结果String*/fun close() : String {return Ch34xAction.close()}/*** 配置设备参数* @return 执行结果String*/fun config() : String {return Ch34xAction.config()}/*** 发出设备状态请求* @return 执行结果String*/fun requestState() : String {return Ch34xAction.write( "FF")}/*** 数据写入设备* @return 执行结果String*/private fun write(outputString: String) : String {return Ch34xAction.write(outputString)}}