Write raw data to USB device on Android.

Unlike USB Serial plugin, this plugin DOES NOT use serial protocol.

For example this can be use to print on USB POS printer by sending ESC\POS bytes.

Only devices with USB Host support (USB OTG) can communicate with USB devices.

Potentially you can write to any USB device (see Limitations).

Plugin has been tested with multiple USB POS printers.

• list connected USB devices
• creates stream to listen on USB attached/detached events
• obtain permissions automatically (see Permissions)
• open connection to selected USB device
• send bytes to USB devices using open connection
• close open connection
• send controlTransfer bytes

• doesn't suppport receiving messages over USB connection (IE. out of paper message)
• connection is fixed to first interface on selected USB device.
• only supports USB_ENDPOINT_XFER_BULK endpoints
• only supports USB endpoints where direction is NOT USB_DIR_IN

If you don't mind asking for permission everytime USB device is physically connected to Android device there's nothing to do. Plugin will ask for permissions when needed. However if you don't want to ask for permission everytime USB device is physically connected add

	<intent-filter>
		<action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" />
	</intent-filter>

	<meta-data android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED"
		android:resource="@xml/device_filter" />

to your AndroidManifest.xml

and place device_filter.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <!-- 0x1CBE / 0x0003: USB POS printer 58 mm -->
    <usb-device vendor-id="7358" product-id="3" />
    <!-- 0x1CB0 / 0x0003: USB POS printer 58 mm -->
    <usb-device vendor-id="7344" product-id="3" />
    <!-- 0x0483 / 0x5740: USB POS printer 58 mm -->
    <usb-device vendor-id="1155" product-id="22336" />
    <!-- 0x0493 / 0x8760: USB POS printer 58 mm -->
    <usb-device vendor-id="1171" product-id="34656" />
    <!-- 0x0416 / 0x5011: USB POS printer 58 mm (Issyzone Pos IMP006B) -->
    <usb-device vendor-id="1046" product-id="20497" />
    <!-- 0x0416 / 0xAABB: USB POS printer 58 mm -->
    <usb-device vendor-id="1046" product-id="43707" />
    <!-- 0x1659 / 0x8965: USB POS printer 58 mm -->
    <usb-device vendor-id="5721" product-id="35173" />
    <!-- 0x0483 / 0x5741: USB POS printer 58 mm -->
    <usb-device vendor-id="1155" product-id="22337" />
    <!-- 0x4B43 / 0x3830: USB POS printer 80 mm (GoojPrt MTP-3) -->
    <usb-device vendor-id="19267" product-id="14384" />
    <!-- 0x0525 / 0xA700: USB POS printer 80 mm (MicroPOS WTP100II) -->
    <usb-device vendor-id="1317" product-id="42752" />
    <!-- 0x0525 / 0xA702: USB POS printer 58 mm (Sewoo LK-P20) -->
    <usb-device vendor-id="1317" product-id="42754" />
    <!-- 0x0416 / 0x5011: USB POS printer 58 mm -->
    <usb-device vendor-id="1046" product-id="20497" />      
</resources>

in the res/xml directory (modify accordingly to your devices). This will automatically open your application when USB device is physically connected. Once permission is allowed it won't ask anymore.

First, you'll probably want to list all USB devices connected to you Android device.

try {
      List<UsbDevice> devices = await _flutterUsbWrite.listDevices();
    } on PlatformException catch (e) {
      print(e.message);
    }

Once you found the device, you'll need to open connection before attempting to write. Each time you open connection device will get new deviceId. To open connection always use vid:pid parameters, method will return new UsbDevice object with deviceId value.

  Future<UsbDevice> _connect(UsbDevice device) async {
    try {
      var result = await _flutterUsbWrite.open(
        vendorId: device.vid,
        productId: device.pid,
      );
      return result;
    } on PermissionException {
      print("Not allowed to do that");
      return null;
    } on PlatformException catch (e) {
      print(e.message);
      return null;
    }
  }

After that you can try to write to device. Function returns true if number of bytes written is >= 0;

bool result = await _flutterUsbWrite.write(Uint8List.fromList("Hello world".codeUnits));

Once you're done writing, close connection to release resources.

   Future _disconnect() async {
    try {
      await _flutterUsbWrite.close();
    } on PlatformException catch (e) {
      print(e.message);
    }
  }

For more info see tests and example project.