通过USB电缆使用AOA协议在两个android设备之间建立通信

Question

I am trying to connect two Android devices with API 14+ via USB OTG cable,

but I am getting null values when I was accessing two API s like followings

mUsbManager.getDeviceList();

mUsbManager.getAccessoryList();

Please help me sharing your ideas or any example of sample apps if you have any.

Answer 1

Are you requesting the permission through the intent to even see what is attached?

Are you defining your own custom type and communication layer or trying to do so over adb....? More info here might be good. For now though, you need to know if you can even see the device.

This problem is somewhat defined in the AOA v2 page : https://source.android.com/devices/accessories/aoa2.html

Text copied from : http://mobilemerit.com/android-app-for-usb-host-with-source-code/

private void checkInfo() {
        manager = (UsbManager) getSystemService(Context.USB_SERVICE);
        /*
         * this block required if you need to communicate to USB devices it's
         * take permission to device
         * if you want than you can set this to which device you want to communicate   
         */
        // ------------------------------------------------------------------
        mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(
                ACTION_USB_PERMISSION), 0);
        IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
        registerReceiver(mUsbReceiver, filter);
        // -------------------------------------------------------------------
        HashMap<string , UsbDevice> deviceList = manager.getDeviceList();
        Iterator<usbdevice> deviceIterator = deviceList.values().iterator();
        String i = "";
        while (deviceIterator.hasNext()) {
            device = deviceIterator.next();
            manager.requestPermission(device, mPermissionIntent);
            i += "\n" + "DeviceID: " + device.getDeviceId() + "\n"
                    + "DeviceName: " + device.getDeviceName() + "\n"
                    + "DeviceClass: " + device.getDeviceClass() + " - "
                    + "DeviceSubClass: " + device.getDeviceSubclass() + "\n"
                    + "VendorID: " + device.getVendorId() + "\n"
                    + "ProductID: " + device.getProductId() + "\n";
        }

        textInfo.setText(i);
    }

    private final BroadcastReceiver mUsbReceiver = new BroadcastReceiver() {

        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (ACTION_USB_PERMISSION.equals(action)) {
                synchronized (this) {
                    UsbDevice device = (UsbDevice) intent
                            .getParcelableExtra(UsbManager.EXTRA_DEVICE);
                    if (intent.getBooleanExtra(
                            UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                        if (device != null) {
                            // call method to set up device communication
                        }
                    } else {
                        Log.d("ERROR", "permission denied for device " + device);
                    }
                }
            }
        }
};