从蓝牙打印机打印的 Android 应用程序

Question

我在网上找到的应用程序运行完美，除了单击“发送”按钮时，在文本框中输入内容后，打印机运行，并在打印过程中停止，但程序不会崩溃。我只是好奇我是否使用了错误的 UUID，事实上我什至不知道它是什么。我有下面这个类，这是运行应用程序所需的唯一类，其余是 XML，具有所有三个蓝牙权限；

package com.example.bluetoothprinter;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.TextView;
import android.widget.EditText;
import android.widget.Button;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Set;
import java.util.UUID;

public class MainActivity extends Activity {

// will show the statuses
TextView myLabel;

// will enable user to enter any text to be printed
EditText myTextbox;

// android built in classes for bluetooth operations
BluetoothAdapter mBluetoothAdapter;
BluetoothSocket mmSocket;
BluetoothDevice mmDevice;

OutputStream mmOutputStream;
InputStream mmInputStream;
Thread workerThread;

byte[] readBuffer;
int readBufferPosition;
int counter;
volatile boolean stopWorker;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    try {

        // we are goin to have three buttons for specific functions
        Button openButton = (Button) findViewById(R.id.open);
        Button sendButton = (Button) findViewById(R.id.send);
        Button closeButton = (Button) findViewById(R.id.close);

        myLabel = (TextView) findViewById(R.id.label);
        myTextbox = (EditText) findViewById(R.id.entry);

        // open bluetooth connection
        openButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                try {
                    findBT();
                    openBT();
                } catch (IOException ex) {
                }
            }
        });

        // send data typed by the user to be printed
        sendButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                try {
                    sendData();
                } catch (IOException ex) {
                }
            }
        });

        // close bluetooth connection
        closeButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                try {
                    closeBT();
                } catch (IOException ex) {
                }
            }
        });

    } catch (NullPointerException e) {
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

/*
 * This will find a bluetooth printer device
 */
void findBT() {

    try {
        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

        if (mBluetoothAdapter == null) {
            myLabel.setText("No bluetooth adapter available");
        }

        if (!mBluetoothAdapter.isEnabled()) {
            Intent enableBluetooth = new Intent(
                    BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBluetooth, 0);
        }

        Set<BluetoothDevice> pairedDevices = mBluetoothAdapter
                .getBondedDevices();
        if (pairedDevices.size() > 0) {
            for (BluetoothDevice device : pairedDevices) {

                // OJL411MY29I911JH is the name of the bluetooth printer device shown after scan
                if (device.getName().equals("OJL411MY29I911JH")) {
                    mmDevice = device;
                    break;
                }
            }
        }
        myLabel.setText("Bluetooth Device Found");
    } catch (NullPointerException e) {
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

/*
 * Tries to open a connection to the bluetooth printer device
 */
void openBT() throws IOException {
    try {
        // Standard SerialPortService ID
        UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805f9b34fb");
        mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);
        mmSocket.connect();
        mmOutputStream = mmSocket.getOutputStream();
        mmInputStream = mmSocket.getInputStream();

        beginListenForData();

        myLabel.setText("Bluetooth Opened");
    } catch (NullPointerException e) {
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

/*
 * After opening a connection to bluetooth printer device, 
 * we have to listen and check if a data were sent to be printed.
 */
void beginListenForData() {
    try {
        final Handler handler = new Handler();

        // This is the ASCII code for a newline character
        final byte delimiter = 10;

        stopWorker = false;
        readBufferPosition = 0;
        readBuffer = new byte[1024];

        workerThread = new Thread(new Runnable() {
            public void run() {
                while (!Thread.currentThread().isInterrupted()
                        && !stopWorker) {

                    try {

                        int bytesAvailable = mmInputStream.available();
                        if (bytesAvailable > 0) {
                            byte[] packetBytes = new byte[bytesAvailable];
                            mmInputStream.read(packetBytes);
                            for (int i = 0; i < bytesAvailable; i++) {
                                byte b = packetBytes[i];
                                if (b == delimiter) {
                                    byte[] encodedBytes = new byte[readBufferPosition];
                                    System.arraycopy(readBuffer, 0,
                                            encodedBytes, 0,
                                            encodedBytes.length);
                                    final String data = new String(
                                            encodedBytes, "US-ASCII");
                                    readBufferPosition = 0;

                                    handler.post(new Runnable() {
                                        public void run() {
                                            myLabel.setText(data);
                                        }
                                    });
                                } else {
                                    readBuffer[readBufferPosition++] = b;
                                }
                            }
                        }

                    } catch (IOException ex) {
                        stopWorker = true;
                    }

                }
            }
        });

        workerThread.start();
    } catch (NullPointerException e) {
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

/*
 * This will send data to be printed by the bluetooth printer
 */
void sendData() throws IOException {
    try {

        // the text typed by the user
        String msg = myTextbox.getText().toString();
        msg += "\n";

        mmOutputStream.write(msg.getBytes());

        // tell the user data were sent
        myLabel.setText("Data Sent");

    } catch (NullPointerException e) {
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

/*
 * Close the connection to bluetooth printer.
 */
void closeBT() throws IOException {
    try {
        stopWorker = true;
        mmOutputStream.close();
        mmInputStream.close();
        mmSocket.close();
        myLabel.setText("Bluetooth Closed");
    } catch (NullPointerException e) {
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }
}
}

Answer 1

我在 sendData 函数的末尾添加了运行 closeBT 函数的代码。如果你不关闭连接，我认为它正在发送过程中挂起。

void sendData() throws IOException {
try {

    // the text typed by the user
    String msg = myTextbox.getText().toString();
    msg += "\n";

    mmOutputStream.write(msg.getBytes());

    // tell the user data were sent
    myLabel.setText("Data Sent");

}   catch (NullPointerException e) {
    e.printStackTrace();
     } catch (Exception e) {
    e.printStackTrace();
   }
}