Android打印机--没有设备驱动sdk，自己实现USB打印功能

Android下的设备调试，如果设备提供了驱动，按照厂家的驱动调试即可；设备未提供驱动，只能按照通用的方法进行调试。

对于智能POS、收银机以及其他打印设备，如果厂商不提供打印相关sdk，那么打印功能怎么实现呢？其实我们可以基于USB通信机制，自己去实现打印驱动。

整个实现流程如下

初始化打印机：首先要获取USB管理器；其次要注册监听USB设备插拔变化和请求权限的广播；最后列出所有的USB设备，并且都请求获取USB权限；

实现这个广播接收器：当接收到请求权限的广播时，获取USB设备的引用，android系统会询问你是否允许设备访问，默认为false；当允许了访问之后，会判断USB的引用是否为null, 如果不为空，说明该设备可以连接，否则提示设备拒绝访问；如果接收到已连接的打印设备移除的广播，则要关闭本次连接。

对于获得权限可使用的USB，我们将获取设备的功能集（UsbInterface）和通信通道（UsbEndpoint），然后创建host与device的连接用来传输数据。

最后，我们在需要打印的地方调用上面封装好的打印方法，就可以发送指令来控制已经建立连接的打印机了。

USB打印机实现

/**
* USB打印机
* Created by john on 17-5-10.
*/

public class USBPrinter {

private static final String ACTION_USB_PERMISSION = "com.usb.printer.USB_PERMISSION";

private static USBPrinter mInstance;

private Context mContext;
private UsbDevice mUsbDevice;
private PendingIntent mPermissionIntent;
private UsbManager mUsbManager;
private UsbDeviceConnection mUsbDeviceConnection;

private final BroadcastReceiver mUsbDeviceReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (ACTION_USB_PERMISSION.equals(action)) {
synchronized (this) {
UsbDevice usbDevice = intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
mUsbDevice = usbDevice;
} else {
Toast.makeText(context, "Permission denied for device " + usbDevice, Toast.LENGTH_SHORT).show();
}
}
} else if (UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action)) {
if (mUsbDevice != null) {
Toast.makeText(context, "Device closed", Toast.LENGTH_SHORT).show();
if (mUsbDeviceConnection != null) {
mUsbDeviceConnection.close();
}
}
}
}
};

private USBPrinter() {

}

public static USBPrinter getInstance() {
if (mInstance == null) {
mInstance = new USBPrinter();
}
return mInstance;
}

/**
* 初始化打印机，需要与destroy对应
*
* @param context 上下文
*/
public static void initPrinter(Context context) {
getInstance().init(context);
}

/**
* 销毁打印机持有的对象
*/
public static void destroyPrinter() {
getInstance().destroy();
}

private void init(Context context) {
mContext = context;
mUsbManager = (UsbManager) mContext.getSystemService(Context.USB_SERVICE);
mPermissionIntent = PendingIntent.getBroadcast(mContext, 0, new Intent(ACTION_USB_PERMISSION), 0);
IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
filter.addAction(UsbManager.ACTION_USB_DEVICE_DETACHED);
mContext.registerReceiver(mUsbDeviceReceiver, filter);

// 列出所有的USB设备，并且都请求获取USB权限
HashMap<String, UsbDevice> deviceList = mUsbManager.getDeviceList();

for (UsbDevice device : deviceList.values()) {
mUsbManager.requestPermission(device, mPermissionIntent);
}
}

private void destroy() {
mContext.unregisterReceiver(mUsbDeviceReceiver);

if (mUsbDeviceConnection != null) {
mUsbDeviceConnection.close();
mUsbDeviceConnection = null;
}

mContext = null;
mUsbManager = null;
}

/**
* 打印方法
* @param msg
*/
public void print(String msg) {
final String printData = msg;
if (mUsbDevice != null) {
UsbInterface usbInterface = mUsbDevice.getInterface(0);
for (int i = 0; i < usbInterface.getEndpointCount(); i++) {
final UsbEndpoint ep = usbInterface.getEndpoint(i);
if (ep.getType() == UsbConstants.USB_ENDPOINT_XFER_BULK) {
if (ep.getDirection() == UsbConstants.USB_DIR_OUT) {
mUsbDeviceConnection = mUsbManager.openDevice(mUsbDevice);
if (mUsbDeviceConnection != null) {
Toast.makeText(mContext, "Device connected", Toast.LENGTH_SHORT).show();
mUsbDeviceConnection.claimInterface(usbInterface, true);
new Thread(new Runnable() {
@Override
public void run() {
byte[] bytes = printData.getBytes();
int b = mUsbDeviceConnection.bulkTransfer(ep, bytes, bytes.length, 100000);
Log.i("Return Status", "b-->" + b);
}
}).start();

mUsbDeviceConnection.releaseInterface(usbInterface);
break;
}
}
}
}
} else {
Toast.makeText(mContext, "No available USB print device", Toast.LENGTH_SHORT).show();
}
}
}