0. 前言
在做 USB OTG 通信时，第一步就是要能够获取到 usb 的使用权限，因此特地在此处介绍一下两种我用过的获取 usb 权限方式。

1. 直接在 AndroidManifest.xml 中配置
这种配置方式是在 github 上 usb-serial-for-android 项目中看到的，大家如果有兴趣可以 clone 下来研究一下。

<activity
            android:name=".DeviceListActivity"
            android:label="@string/app_name"
            android:theme="@android:style/Theme.Black.NoTitleBar.Fullscreen">
            <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" />
        </activity>

其中 device_filter.xml 中列出了可用 usb 设备，当usb 设备连接手机之后，app 会自动询问是否允许获取该 usb 的权限。
device_filter.xml 放置位置如下图所示

内容为

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <!-- 0x0403 / 0x6001: FTDI FT232R UART -->
    <usb-device vendor-id="1027" product-id="24577" />

    <!-- 0x0403 / 0x6015: FTDI FT231X -->
    <usb-device vendor-id="1027" product-id="24597" />

    <!-- 0x2341 / Arduino -->
    <usb-device vendor-id="9025" />

    <!-- 0x16C0 / 0x0483: Teensyduino  -->
    <usb-device vendor-id="5824" product-id="1155" />

    <!-- 0x10C4 / 0xEA60: CP210x UART Bridge -->
    <usb-device vendor-id="4292" product-id="60000" />

    <!-- 0x067B / 0x2303: Prolific PL2303 -->
    <usb-device vendor-id="1659" product-id="8963" />

    <!-- 0x1a86 / 0x7523: Qinheng CH340 -->
    <usb-device vendor-id="6790" product-id="29987" />
</resources>

每个 usb 设备通过 vendor-id（厂商 id） 和 product-id （产品 id）一起来定义的，这里有一个 linux 的 usb设备厂商 id 和产品 id 的汇总，可以作为 Android usb 设备的参考。

2. 在代码中获取
这代码是在其他博客中看到的，忘记是哪篇了，这里就不引用了。直接上代码。

    /**
     * 获得 usb 权限
     */
    private void openUsbDevice(){
        //before open usb device
        //should try to get usb permission
        tryGetUsbPermission();
    }
    UsbManager mUsbManager;
    private static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION";

    private void tryGetUsbPermission(){
        mUsbManager = (UsbManager) getSystemService(Context.USB_SERVICE);

        IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
        registerReceiver(mUsbPermissionActionReceiver, filter);

        PendingIntent mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);

        //here do emulation to ask all connected usb device for permission
        for (final UsbDevice usbDevice : mUsbManager.getDeviceList().values()) {
            //add some conditional check if necessary
            //if(isWeCaredUsbDevice(usbDevice)){
            if(mUsbManager.hasPermission(usbDevice)){
                //if has already got permission, just goto connect it
                //that means: user has choose yes for your previously popup window asking for grant perssion for this usb device
                //and also choose option: not ask again
                afterGetUsbPermission(usbDevice);
            }else{
                //this line will let android popup window, ask user whether to allow this app to have permission to operate this usb device
                mUsbManager.requestPermission(usbDevice, mPermissionIntent);
            }
            //}
        }
    }

    private void afterGetUsbPermission(UsbDevice usbDevice){
        //call method to set up device communication
        //Toast.makeText(this, String.valueOf("Got permission for usb device: " + usbDevice), Toast.LENGTH_LONG).show();
        //Toast.makeText(this, String.valueOf("Found USB device: VID=" + usbDevice.getVendorId() + " PID=" + usbDevice.getProductId()), Toast.LENGTH_LONG).show();

        doYourOpenUsbDevice(usbDevice);
    }

    private void doYourOpenUsbDevice(UsbDevice usbDevice){
        //now follow line will NOT show: User has not given permission to device UsbDevice
        UsbDeviceConnection connection = mUsbManager.openDevice(usbDevice);
        //add your operation code here
    }

    private final BroadcastReceiver mUsbPermissionActionReceiver = new BroadcastReceiver() {
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (ACTION_USB_PERMISSION.equals(action)) {
                synchronized (this) {
                    UsbDevice usbDevice = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                    if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                        //user choose YES for your previously popup window asking for grant perssion for this usb device
                        if(null != usbDevice){
                            afterGetUsbPermission(usbDevice);
                        }
                    }
                    else {
                        //user choose NO for your previously popup window asking for grant perssion for this usb device
                        Toast.makeText(context, String.valueOf("Permission denied for device" + usbDevice), Toast.LENGTH_LONG).show();
                    }
                }
            }
        }
    };