我对Android中的USB连接没有太多经验，所以我按照Android developer page上的教程进行操作。我试图整理一个代码，当我向USB设备发送命令时，例如
send("M?");
然后设备将我的应用程序处理并显示给我的一些字符串行发回给我。但不幸的是，我没有得到我想要的东西。有时我只得到那个字符串的一部分，有时是一些奇怪的字符，或者什么也没有。你能帮帮我，如何修复我的代码？此代码应该能够读取小字符串（例如20-25个字符），但也可以读取长字符串。
我有以下代码：
UsbReadWrite.java
public class UsbReadWrite extends AppCompatActivity {
static UsbDevice device;
private static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION";
static UsbManager mUsbManager;
static PendingIntent mPermissionIntent;
private static byte[] bytes;
private static boolean forceClaim = true;
static int controlTransferResult;
static byte[] readBytes = new byte[4096];
static UsbEndpoint epOut = null, epIn = null;
static UsbDeviceConnection connection;
static int recvBytes;
static String readString = "";
static Thread thread;
static Runnable r;
static UsbInterface intf;
static UsbRequest request;
Handler handler;
static UsbManager manager;
static HashMap<String, UsbDevice> deviceList;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
public UsbReadWrite(Handler handler){
this.handler = handler;
}
public static boolean connectDevice(Context context){
manager = (UsbManager) context.getSystemService(Context.USB_SERVICE);
deviceList = manager.getDeviceList();
if (deviceList.toString().equals("{}")) {
return false;
}
Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();
device = deviceIterator.next();
mUsbManager = (UsbManager) context.getSystemService(Context.USB_SERVICE);
mPermissionIntent = PendingIntent.getBroadcast(context, 0, new Intent(ACTION_USB_PERMISSION), 0);
IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
try {
context.registerReceiver(mUsbReceiver, filter);
}catch (Exception e){
e.printStackTrace();
}
mUsbManager.requestPermission(device, mPermissionIntent);
intf = device.getInterface(0);
// look for our bulk endpoints
for (int i = 0; i < intf.getEndpointCount(); i++) {
UsbEndpoint ep = intf.getEndpoint(i);
if (ep.getType() == UsbConstants.USB_ENDPOINT_XFER_BULK) {
if (ep.getDirection() == UsbConstants.USB_DIR_OUT) {
epOut = ep;
} else if (ep.getDirection() == UsbConstants.USB_DIR_IN) {
epIn = ep;
}
}
}
if (epOut == null || epIn == null) {
throw new IllegalArgumentException("Not all endpoints found.");
}
Thread t = new Thread(new Runnable() {
@Override
public void run() {
while (!mUsbManager.hasPermission(device)){
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
connection = mUsbManager.openDevice(device);
connection.claimInterface(intf, forceClaim);
connection.controlTransfer(0x40, 0, 0, 0, null, 0, 0);// reset
connection.controlTransfer(0x40, 0, 1, 0, null, 0, 0);// clear Rx
connection.controlTransfer(0x40, 0, 2, 0, null, 0, 0);// clear Tx
controlTransferResult = connection.controlTransfer(0x40, 0x03, 0x4138, 0, null, 0, 0);
connection.controlTransfer(0x40, 0x04, 0x0008, 0, null, 0, 0);
request = new UsbRequest();
request.initialize(connection, epOut);
}
});
t.start();
return true;
}
public static final BroadcastReceiver mUsbReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (ACTION_USB_PERMISSION.equals(action)) {
synchronized (this) {
UsbDevice device = (UsbDevice) intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
if (device != null) {
//call method to set up device communication
intf = device.getInterface(0);
// look for our bulk endpoints
for (int i = 0; i < intf.getEndpointCount(); i++) {
UsbEndpoint ep = intf.getEndpoint(i);
if (ep.getType() == UsbConstants.USB_ENDPOINT_XFER_BULK) {
if (ep.getDirection() == UsbConstants.USB_DIR_OUT) {
epOut = ep;
} else if (ep.getDirection() == UsbConstants.USB_DIR_IN) {
epIn = ep;
}
}
}
if (epOut == null || epIn == null) {
throw new IllegalArgumentException("Not all endpoints found.");
}
connection = mUsbManager.openDevice(device);
connection.claimInterface(intf, forceClaim);
connection.controlTransfer(0x40, 0, 0, 0, null, 0, 0);// reset
connection.controlTransfer(0x40, 0, 1, 0, null, 0, 0);// clear Rx
connection.controlTransfer(0x40, 0, 2, 0, null, 0, 0);// clear Tx
controlTransferResult = connection.controlTransfer(0x40, 0x03, 0x4138, 0, null, 0, 0);
connection.controlTransfer(0x40, 0x04, 0x0008, 0, null, 0, 0);
request = new UsbRequest();
request.initialize(connection, epOut);
}
} else {
Log.d("MyActivity", "permission denied for device " + device);
}
}
}
}
};
public static void read2(){
r = new Runnable() {
@Override
public void run() {
synchronized (this) {
readString="";
send("M?");
while (true) {
try {
Thread.sleep(400);
} catch (InterruptedException e) {
e.printStackTrace();
}
if (mUsbManager.hasPermission(device)){
recvBytes = connection.bulkTransfer(epIn, readBytes, readBytes.length, 100);
Log.e("Database","M?="+readBytes);
if (recvBytes != 0) {
readString += new String(readBytes);
readString = readString.replace("\u0001`","");
readString = readString.replace("\u0000","");
Log.e("Database","M?="+readString);
}
}
}
}
}
};
thread = new Thread(r);
thread.start();
}
public static void send(String command){
String fullCommand = "@" + command + "\r\n"; /*+ "\r\n"*/
bytes = fullCommand.getBytes();
while (connection==null){
continue;
}
connection.bulkTransfer(epOut, bytes, bytes.length, 100); //0
}
}
提前致谢。