我有一个 Java 应用程序通过 USB 向 Android 设备发送字节,问题是它似乎没有在 Android 端读取任何字节
以下是信息的发送方式
private static void writeAndRead() throws LibUsbException {
String question = "Hello Android I'll be your host today, how are you?";
byte[] questionBuffer = question.getBytes();
ByteBuffer questionData = BufferUtils.allocateByteBuffer(questionBuffer.length);
IntBuffer transferred = IntBuffer.allocate(1);
int result = 0;
System.out.println("Sending question: " + question);
System.out.println("Length of buffer: " + questionBuffer.length);
result = LibUsb.bulkTransfer(handle, END_POINT_OUT_ACC, questionData, transferred, 5000);
if(result < 0) {
throw new LibUsbException("Bulk write error!", result);
}
}
此方法似乎完成时没有引发异常,并且报告已发送了长度为 51 的缓冲区。
在 Android 端,我有以下内容
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private UsbManager manager;
private UsbAccessory accessory;
private ParcelFileDescriptor accessoryFileDescriptor;
private FileInputStream accessoryInput;
private FileOutputStream accessoryOutput;
private String question = "";
private TextView questionTV;
Runnable updateUI = new Runnable() {
@Override
public void run() {
questionTV.append(question);
}
};
Runnable readQuestionTask = new Runnable() {
@Override
public void run() {
byte[] buffer = new byte[51];
int ret;
try {
ret = accessoryInput.read(buffer);
Log.d(TAG, "Read: " +ret);
if (ret == 51) {
String msg = new String(buffer);
question += " Question: " + msg;
} else {
question += " Read error";
}
Log.d(TAG, question);
} catch (IOException e) {
Log.e(TAG, "Read error ", e);
question += " Read error";
}
questionTV.post(updateUI);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
questionTV = (TextView) findViewById(R.id.hello_world);
questionTV.setMovementMethod(new ScrollingMovementMethod());
Intent intent = getIntent();
manager = (UsbManager) getSystemService(Context.USB_SERVICE);
accessory = intent.getParcelableExtra(UsbManager.EXTRA_ACCESSORY);
if(accessory == null) {
questionTV.append("Not started by the accessory itself"
+ System.getProperty("line.separator"));
return;
}
Log.d(TAG, accessory.toString());
accessoryFileDescriptor = manager.openAccessory(accessory);
Log.d(TAG, "File Descriptor " +accessoryFileDescriptor.toString());
if (accessoryFileDescriptor != null) {
FileDescriptor fd = accessoryFileDescriptor.getFileDescriptor();
accessoryInput = new FileInputStream(fd);
accessoryOutput = new FileOutputStream(fd);
}
new Thread(readQuestionTask).start();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
以下代码段
try {
ret = accessoryInput.read(buffer);
Log.d(TAG, "Read: " +ret);
if (ret == 51) {
String msg = new String(buffer);
question += " Question: " + msg;
} else {
question += " Read error";
}
Log.d(TAG, question);
} catch (IOException e) {
Log.e(TAG, "Read error ", e);
question += " Read error";
}
在控制台中报告问题
字符串的内容
09-18 09:58:30.084 26198-26221/com.example.paulstatham.testusb D/MainActivity﹕ Read: 51
09-18 09:58:30.084 26198-26221/com.example.paulstatham.testusb D/MainActivity﹕ Question: ������������������������������������������������������������������������������������������������������
Activity 本身仅将其显示为“问题:”
我假设这些奇怪的字符只是首次分配字节数组时的默认字节值byte[] buffer = new byte[51];
不幸的是,该应用程序的性质使其很难调试。
关于为什么 ret =accessoryInput.read(buffer);
似乎没有读取任何内容,有什么建议吗?
编辑:实际上它正在读取一些内容,因为 accessoryInput.read(buffer);
将阻塞直到有输入,并且它不会阻塞。
那么为什么byte[]
充满了垃圾?
我认为这可能与发送 ByteBuffer 的事实有关
LibUsb.bulkTransfer(handle, END_POINT_OUT_ACC, questionData, transferred, 5000);
但我尝试在 Android 中转换它
ByteBuffer buf = ByteBuffer.wrap(buffer);
String msg = new String(buf.array());
question += " Question: " + msg;
它给了我同样的垃圾字符
最佳答案
再次回答我自己的问题,问题就在这里
String question = "Hello Android I'll be your host today, how are you?";
byte[] questionBuffer = question.getBytes();
ByteBuffer questionData = BufferUtils.allocateByteBuffer(questionBuffer.length);
IntBuffer transferred = IntBuffer.allocate(1);
我实际上从未将byte[]
放入ByteBuffer
questionData.put(questionBuffer)
解决了问题!
关于java - 通过 USB 将数据发送到 Android 应用程序,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/32648345/