UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
Reader reader = new Reader(manager);

If you want to detect a card in your application, you can supply a Reader.OnStateChangeListener object to Reader object.

reader.setOnStateChangeListener(new OnStateChangeListener() {

    @Override
    public void onStateChange(int slotNum, int prevState, int currState) {

        // TODO: Add your code here
    }
});

Opening Reader

To open a reader, you need to get a UsbDevice object from UsbManager and request a permission to access the device or discover a device using intent filter. For more information, please refer to USB Host from Android Dev Guide.

try {

    reader.open(device);

} catch (IllegalArgumentException e) {

    e.printStackTrace();
}

It will throw IllegalArgumentException if the UsbDevice object is not supported or it cannot be opened due to communication error.

Closing Reader

Android will not close the USB device automatically if you close the application. You cannot use the reader without unplugging it when you start the application next time. Therefore, it is advised to close the reader before closing the application.

reader.close();

Resetting Card

Before transmitting APDU command, you need to power up a card first. The ATR string will be returned if the card is operated normally. Otherwise, it will throw a exception to indicate the error.

try {

    byte[] atr = reader.power(slotNum, Reader.CARD_WARM_RESET);

} catch (ReaderException e) {

    e.printStackTrace();
}

Setting Protocol

After powering up the card, the card state is changed to Negotiable (Reader.CARD_NEGOTIABLE) or Specific (Reader.CARD_SPECIFIC). You cannot transmit a APDU command if the card state is not equal to Specific. To select a protocol, invoke Reader.setProtocol() method with preferred protocols.

try {

    reader.setProtocol(slotNum, Reader.PROTOCOL_T0 | Reader.PROTOCOL_T1);

} catch (ReaderException e) {

    e.printStackTrace();
}

Transmitting APDU

After selecting the protcol, you can transmit the APDU command using Reader.transmit().

byte[] command = { 0x00, 0x84, 0x00, 0x00, 0x08 };
byte[] response = new byte[300];
int responseLength;

try {

    responseLength = reader.transmit(slotNum, command, command.length, response,
            response.length);

} catch (ReaderException e) {

    e.printStackTrace();
}

Controlling Reader

You can control the reader using Reader.control() if the reader supports a set of escape commands.

// Get firmware version (ACR122)
byte[] command = { 0xFF, 0x00, 0x48, 0x00, 0x08 };

byte[] response = new byte[300];
int responseLength;

try {

    responseLength = reader.control(slotNum, Reader.IOCTL_CCID_ESCAPE, command,
            command.length, response, response.length);

} catch (ReaderException e) {

    e.printStackTrace();
}