Android USB Host Mode and Accessory Mode

问题:

I am trying to learn Android USB Host/Accessory connection. I read android devices can act usb host or usb accessory. Therefore I create two project one of them usb host project, other usb accessory project. I installed these projects to two different android devices. One of them has usb host(Device A) project, other has usb accessory(Device B) project.

My question is, I can connect with usb host project to Device B. I can see all information about device. But In accessory project( Device B) i can not see any thing about device A.

manager.getAccessoryList() always return null. My usb accessory project code is here.

UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);

for (UsbAccessory accessory : manager.getAccessoryList()) {
    String list = " DESCRIPTION : " + accessory.getDescription() + " MODEL : " + accessory.getModel() + " MANUFACTURER : " + accessory.getManufacturer() + " SERIAL : " + accessory.getSerial();
    Toast.makeText(this, list, Toast.LENGTH_LONG).show();
}

回答1:

That's because when you connect an accessory to Device B, your accessory which is acting as US B host must implement the Android Open Accessory Protocol (AOAP). See Connecting over USB. Since Device A (host), does not implement the AOAP, Device B will refuse to communicate with Device A beyond a handshake attemp.

回答2:

Try this https://github.com/quandoo/android2android-accessory

Even I was getting accessory list as 0. But in the github project, they have first sent some control message from one android device acting as a host to other device which is accessory. After sending the control message, I get the accessory list non-zero.