Implement openDevice/closeDevice method of MtpManager.

package com.android.mtp;

import android.content.Context;

import android.hardware.usb.UsbDevice;

import android.hardware.usb.UsbDeviceConnection;

import android.hardware.usb.UsbManager;

import android.mtp.MtpDevice;

import android.util.SparseArray;

import java.io.IOException;

 * The model wrapping android.mtp API.

 */

class MtpManager {

    private final UsbManager mManager;

    // TODO: Save and restore the set of opened device.

    private final SparseArray<MtpDevice> mDevices = new SparseArray<MtpDevice>();

    MtpManager(Context context) {

        mManager = (UsbManager)context.getSystemService(Context.USB_SERVICE);

    }

    synchronized void openDevice(int deviceId) throws IOException {

        UsbDevice rawDevice = null;

        for (final UsbDevice candidate : mManager.getDeviceList().values()) {

            if (candidate.getDeviceId() == deviceId) {

                rawDevice = candidate;

                break;

            }

        }

        if (rawDevice == null) {

            throw new IOException("Not found USB device: " + deviceId);

        }

        if (!mManager.hasPermission(rawDevice)) {

            // Permission should be obtained via app selection dialog for intent.

            throw new IOException("No parmission to operate USB device.");

        }

        final MtpDevice device = new MtpDevice(rawDevice);

    void openDevice(int deviceId) throws IOException {

        // TODO: Implement this method.

        final UsbDeviceConnection connection = mManager.openDevice(rawDevice);

        if (connection == null) {

            throw new IOException("Failed to open a USB connection.");

        }

    void closeDevice(int deviceId) throws IOException {

        // TODO: Implement this method.

        if (!device.open(connection)) {

            throw new IOException("Failed to open a MTP device.");

        }

    int[] getOpenedDeviceIds() {

        // TODO: Implement this method.

        return null;

        // Handle devices that fail to obtain storages just after opening a MTP session.

        final int[] storageIds = device.getStorageIds();

        if (storageIds == null || storageIds.length == 0) {

            throw new IOException("Not found MTP storages in the device.");

        }

        mDevices.put(deviceId, device);

    }

    synchronized void closeDevice(int deviceId) throws IOException {

        final MtpDevice device = mDevices.get(deviceId);

        if (device == null) {

            throw new IOException("USB device " + deviceId + " is not opened.");

        }

        mDevices.get(deviceId).close();

        mDevices.remove(deviceId);

    }

    synchronized int[] getOpenedDeviceIds() {

        final int[] result = new int[mDevices.size()];

        for (int i = 0; i < result.length; i++) {

            result[i] = mDevices.keyAt(i);

        }

        return result;

    }

}