具体原理这里就不说了　我也没理顺　网上有很多文章都说的很清楚 这里我就直接上重点

主要修改文件

frameworks/base/service/java/com/android/server/usb/UsbService.java

frameworks/base/service/java/com/android/server/usb/UsbHostManager.java

首先将UsbService.java中的public UsbService(Context context)改为这样

    public UsbService(Context context) {
        mContext = context;
        mSettingsManager = new UsbSettingsManager(context);
        PackageManager pm = mContext.getPackageManager();
        //if (pm.hasSystemFeature(PackageManager.FEATURE_USB_HOST)) {//modify by hclydao
            mHostManager = new UsbHostManager(context, mSettingsManager);
        //}
        if (new File("/sys/class/android_usb").exists()) {
            mDeviceManager = new UsbDeviceManager(context, mSettingsManager);
        }
    }

接下来主要就是修改usbhostmanager了 当硬件usb host插入里会执行usbhostmanager里的usbDeviceAdded函数　拔掉时会执行usbDeviceRemoved

当设备插入时在usb jni里会回调usbDeviceAdded函数　此时会传回这个usb设备的相关信息　但是发现class都是０　还好　在int [] interfaceValues传回了整个usb相关信息interfaceValues[1] 对应的就是相应的class 3对应的是usb hid 8对应的是mass storage 9对就的是usb hub　提示图片和信息直接使用系统自带的

最后修改为如下

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions an
 * limitations under the License.
 */

package com.android.server.usb;

import android.app.PendingIntent;
import android.content.BroadcastReceiver;
import android.content.ContentResolver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.hardware.usb.IUsbManager;
import android.hardware.usb.UsbConstants;
import android.hardware.usb.UsbDevice;
import android.hardware.usb.UsbEndpoint;
import android.hardware.usb.UsbInterface;
import android.hardware.usb.UsbManager;
import android.net.Uri;
import android.os.Binder;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.os.Parcelable;
import android.os.ParcelFileDescriptor;
import android.os.UEventObserver;
import android.provider.Settings;
import android.util.Slog;

import java.io.File;
import java.io.FileDescriptor;
import java.io.FileReader;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.List;
import android.app.Notification;
import android.app.NotificationManager;
import android.content.res.Resources;
import java.util.ArrayList;
/**
 * UsbHostManager manages USB state in host mode.
 */
public class UsbHostManager {
    private static final String TAG = UsbHostManager.class.getSimpleName();
    private static final boolean LOG = false;

    // contains all connected USB devices
    private final HashMap<String,UsbDevice> mDevices = new HashMap<String,UsbDevice>();

    // USB busses to exclude from USB host support
    private final String[] mHostBlacklist;

    private final Context mContext;
    private final Object mLock = new Object();
    private final UsbSettingsManager mSettingsManager;
	private Notification mUsbHostNotification;
	private ArrayList<String> dlist;
    public UsbHostManager(Context context, UsbSettingsManager settingsManager) {
        mContext = context;
        mSettingsManager = settingsManager;
        mHostBlacklist = context.getResources().getStringArray(
                com.android.internal.R.array.config_usbHostBlacklist);
    }

    private boolean isBlackListed(String deviceName) {
        int count = mHostBlacklist.length;
        for (int i = 0; i < count; i++) {
            if (deviceName.startsWith(mHostBlacklist[i])) {
                return true;
            }
        }
        return false;
    }

    /* returns true if the USB device should not be accessible by applications */
    private boolean isBlackListed(int clazz, int subClass, int protocol) {
        // blacklist hubs
        if (clazz == UsbConstants.USB_CLASS_HUB) return true;

        // blacklist HID boot devices (mouse and keyboard)
        if (clazz == UsbConstants.USB_CLASS_HID &&
                subClass == UsbConstants.USB_INTERFACE_SUBCLASS_BOOT) {
            return true;
        }

        return false;
    }

    /* Called from JNI in monitorUsbHostBus() to report new USB devices */
    private void usbDeviceAdded(String deviceName, int vendorID, int productID,
            int deviceClass, int deviceSubclass, int deviceProtocol,
            /* array of quintuples containing id, class, subclass, protocol
               and number of endpoints for each interface */
            int[] interfaceValues,
           /* array of quadruples containing address, attributes, max packet size
              and interval for each endpoint */
            int[] endpointValues) {
		if((interfaceValues != null) && (interfaceValues[1] == UsbConstants.USB_CLASS_HID)) {//add by hclydao
            setUsbHostNotification(
                    com.android.internal.R.string.usb_storage_notification_title,
                    com.android.internal.R.string.usb_storage_notification_title,
                    com.android.internal.R.drawable.stat_sys_tether_usb, true, true, null);
			if(dlist == null)
				dlist = new ArrayList<String>();
			dlist.add(deviceName);
		}
        if (isBlackListed(deviceName) ||
                isBlackListed(deviceClass, deviceSubclass, deviceProtocol)) {
            return;
        }

        synchronized (mLock) {
            if (mDevices.get(deviceName) != null) {
                Slog.w(TAG, "device already on mDevices list: " + deviceName);
                return;
            }

            int numInterfaces = interfaceValues.length / 5;
            Parcelable[] interfaces = new UsbInterface[numInterfaces];
            try {
                // repackage interfaceValues as an array of UsbInterface
                int intf, endp, ival = 0, eval = 0;
                for (intf = 0; intf < numInterfaces; intf++) {
                    int interfaceId = interfaceValues[ival++];
                    int interfaceClass = interfaceValues[ival++];
                    int interfaceSubclass = interfaceValues[ival++];
                    int interfaceProtocol = interfaceValues[ival++];
                    int numEndpoints = interfaceValues[ival++];

                    Parcelable[] endpoints = new UsbEndpoint[numEndpoints];
                    for (endp = 0; endp < numEndpoints; endp++) {
                        int address = endpointValues[eval++];
                        int attributes = endpointValues[eval++];
                        int maxPacketSize = endpointValues[eval++];
                        int interval = endpointValues[eval++];
                        endpoints[endp] = new UsbEndpoint(address, attributes,
                                maxPacketSize, interval);
                    }

                    // don't allow if any interfaces are blacklisted
                    if (isBlackListed(interfaceClass, interfaceSubclass, interfaceProtocol)) {
                        return;
                    }
                    interfaces[intf] = new UsbInterface(interfaceId, interfaceClass,
                            interfaceSubclass, interfaceProtocol, endpoints);
                }
            } catch (Exception e) {
                // beware of index out of bound exceptions, which might happen if
                // a device does not set bNumEndpoints correctly
                Slog.e(TAG, "error parsing USB descriptors", e);
                return;
            }

            UsbDevice device = new UsbDevice(deviceName, vendorID, productID,
                    deviceClass, deviceSubclass, deviceProtocol, interfaces);
            mDevices.put(deviceName, device);
            mSettingsManager.deviceAttached(device);
        }
    }

    /* Called from JNI in monitorUsbHostBus to report USB device removal */
    private void usbDeviceRemoved(String deviceName) {
		if(dlist != null) {
			for(int i = 0;i<dlist.size();i++) {
				if(dlist.get(i).equals(deviceName)) {
					dlist.remove(i);
/*
				    setUsbHostNotification(
				            com.android.internal.R.string.ext_media_nomedia_notification_title,
				            com.android.internal.R.string.ext_media_nomedia_notification_message,
				            com.android.internal.R.drawable.stat_sys_tether_usb,
				            false, false, null);
*/
					setUsbHostNotification(0, 0, 0, false, false, null);
					break;
				}
			}
		}
        synchronized (mLock) {
            UsbDevice device = mDevices.remove(deviceName);
            if (device != null) {
                mSettingsManager.deviceDetached(device);
            }
        }		
    }

    public void systemReady() {
        synchronized (mLock) {
            // Create a thread to call into native code to wait for USB host events.
            // This thread will call us back on usbDeviceAdded and usbDeviceRemoved.
            Runnable runnable = new Runnable() {
                public void run() {
                    monitorUsbHostBus();
                }
            };
            new Thread(null, runnable, "UsbService host thread").start();
        }
    }

    /* Returns a list of all currently attached USB devices */
    public void getDeviceList(Bundle devices) {
        synchronized (mLock) {
            for (String name : mDevices.keySet()) {
                devices.putParcelable(name, mDevices.get(name));
            }
        }
    }

    /* Opens the specified USB device */
    public ParcelFileDescriptor openDevice(String deviceName) {
        synchronized (mLock) {
            if (isBlackListed(deviceName)) {
                throw new SecurityException("USB device is on a restricted bus");
            }
            UsbDevice device = mDevices.get(deviceName);
            if (device == null) {
                // if it is not in mDevices, it either does not exist or is blacklisted
                throw new IllegalArgumentException(
                        "device " + deviceName + " does not exist or is restricted");
            }
            mSettingsManager.checkPermission(device);
            return nativeOpenDevice(deviceName);
        }
    }

    public void dump(FileDescriptor fd, PrintWriter pw) {
        synchronized (mLock) {
            pw.println("  USB Host State:");
            for (String name : mDevices.keySet()) {
                pw.println("    " + name + ": " + mDevices.get(name));
            }
        }
    }

    private synchronized void setUsbHostNotification(int titleId, int messageId, int icon, boolean visible,
                                                          boolean dismissable, PendingIntent pi) {

        if (!visible && mUsbHostNotification == null) {
            return;
        }

        NotificationManager notificationManager = (NotificationManager) mContext
                .getSystemService(Context.NOTIFICATION_SERVICE);

        if (notificationManager == null) {
            return;
        }

        if (mUsbHostNotification != null && visible) {
            /*
             * Dismiss the previous notification - we're about to
             * re-use it.
             */
            final int notificationId = mUsbHostNotification.icon;
            notificationManager.cancel(notificationId);
        }
        
        if (visible) {
            Resources r = Resources.getSystem();
            CharSequence title = r.getText(titleId);
            CharSequence message = r.getText(messageId);

            if (mUsbHostNotification == null) {
                mUsbHostNotification = new Notification();
                mUsbHostNotification.when = 0;
            }

            mUsbHostNotification.defaults &= ~Notification.DEFAULT_SOUND;

            if (dismissable) {
                mUsbHostNotification.flags = Notification.FLAG_AUTO_CANCEL;
            } else {
                mUsbHostNotification.flags = Notification.FLAG_ONGOING_EVENT;
            }

            mUsbHostNotification.tickerText = title;
            if (pi == null) {
                Intent intent = new Intent();
                pi = PendingIntent.getBroadcast(mContext, 0, intent, 0);
            }

            mUsbHostNotification.icon = icon;
            mUsbHostNotification.setLatestEventInfo(mContext, title, message, pi);
        }
    
        final int notificationId = mUsbHostNotification.icon;
        if (visible) {
            notificationManager.notify(notificationId, mUsbHostNotification);
        } else {
            notificationManager.cancel(notificationId);
        }
    }

    private native void monitorUsbHostBus();
    private native ParcelFileDescriptor nativeOpenDevice(String deviceName);
}

android4.0 hid插入提示