Question

我有一个Java应用程序通过USB向Android设备发送字节，问题是它似乎没有读取Android端的任何字节

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);
    }
}

此方法似乎在不抛出异常的情况下完成，并且报告它发送的缓冲区长度为51。

在Android方面，我有以下

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);
    }

}

以下代码部分

        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question字符串的内容为

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: ������������������������������������������������������������������������������������������������������

活动本身只是将其显示为“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，应用程序的性质使得调试非常困难。

有关为什么ret = accessoryInput.read(buffer);似乎没有阅读任何内容的任何建议？

编辑：实际上正在读取内容，因为accessoryInput.read(buffer);会阻止，直到有输入，并且它没有阻止。

那么为什么byte[]充满垃圾？

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;

它给了我相同的垃圾字符

Answer 1

然后再回答我自己的问题，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);

我从未真正将byte[]放入ByteBuffer

questionData.put(questionBuffer)解决了这个问题！

通过USB将数据发送到Android应用

1 个答案: