转载请注明出处：http://blog.csdn.net/droyon/article/details/45098027
1、android背景介绍
UsbService，在系统启动时创建，在该文件中，和usb状态息息相关的操作类是UsbDeviceManager，大部分的usb以及adb相关的逻辑，在这个类中做处理。UsbDeviceManager中，我们需要关注三部分内容。一、配置文件。二、 private final UEventObserver mUEventObserver = new UEventObserver() ，接受UEvent事件。三、UsbHandler。
其中配置文件，保存当前usb状态。UEventObserver接受usb事件，push给UsbHandler来处理。UsbHandler是用来处理Usb事件的关键类。
2、Usb默认状态从哪里获取，当前的默认状态又是什么？
Usb的当前状态保存在mCurrentFunctions成员变量中，该变量在UsbHandler的构造中进行初始化。
mDefaultFunctions = SystemProperties.get("persist.sys.usb.config", "adb"); // Check if USB mode needs to be overridden depending on OEM specific bootmode. mDefaultFunctions = processOemUsbOverride(mDefaultFunctions); // sanity check the sys.usb.config system property // this may be necessary if we crashed while switching USB configurations String config = SystemProperties.get("sys.usb.config", "none"); if (!config.equals(mDefaultFunctions)) { Slog.w(TAG, "resetting config to persistent property: " + mDefaultFunctions); SystemProperties.set("sys.usb.config", mDefaultFunctions); } mCurrentFunctions = mDefaultFunctions;3、插入usb时，弹出adb以及Notification通知的大体流程是什么？
插入usb时，我们的UEventObserver会收到信息，最终push给UsbHandler。
UEvent信息：
04-17 14:20:03.352 V/UsbDeviceManager( 759): USB UEVENT: {USB_STATE=DISCONNECTED, SUBSYSTEM=android_usb, SEQNUM=7528, ACTION=change, DEVPATH=/devices/virtual/android_usb/android0}然后执行UsbHandler的updateState方法。private final UEventObserver mUEventObserver = new UEventObserver() { @Override public void onUEvent(UEventObserver.UEvent event) { if (DEBUG) Slog.v(TAG, "USB UEVENT: " + event.toString()); String state = event.get("USB_STATE"); String accessory = event.get("ACCESSORY"); if (state != null) { mHandler.updateState(state); } else if ("START".equals(accessory)) { if (DEBUG) Slog.d(TAG, "got accessory start"); startAccessoryMode(); } } };updateState方法：更新mConnection状态。
public void updateState(String state) { int connected, configured; if ("DISCONNECTED".equals(state)) { connected = 0; configured = 0; } else if ("CONNECTED".equals(state)) { connected = 1; configured = 0; } else if ("CONFIGURED".equals(state)) { connected = 1; configured = 1; } else { Slog.e(TAG, "unknown state " + state); return; } removeMessages(MSG_UPDATE_STATE); Message msg = Message.obtain(this, MSG_UPDATE_STATE); msg.arg1 = connected; msg.arg2 = configured; // debounce disconnects to avoid problems bringing up USB tethering sendMessageDelayed(msg, (connected == 0) ? UPDATE_DELAY : 0); }最后在UsbHandler中进行更新状态，进而弹出adb以及usb的Notificationcase MSG_UPDATE_STATE: mConnected = (msg.arg1 == 1); mConfigured = (msg.arg2 == 1); updateUsbNotification(); updateAdbNotification(); if (containsFunction(mCurrentFunctions, UsbManager.USB_FUNCTION_ACCESSORY)) { updateCurrentAccessory(); } else if (!mConnected) { // restore defaults when USB is disconnected setEnabledFunctions(mDefaultFunctions, false); } if (mBootCompleted) { updateUsbState(); updateAudioSourceFunction(); } break;4、可设置的usb类型有哪些？public static final String USB_FUNCTION_MASS_STORAGE = "mass_storage"; /** * Name of the adb USB function. * Used in extras for the [email protected] #ACTION_USB_STATE} broadcast * * [email protected]} */ public static final String USB_FUNCTION_ADB = "adb"; /** * Name of the RNDIS ethernet USB function. * Used in extras for the [email protected] #ACTION_USB_STATE} broadcast * * [email protected]} */ public static final String USB_FUNCTION_RNDIS = "rndis"; /** * Name of the MTP USB function. * Used in extras for the [email protected] #ACTION_USB_STATE} broadcast * * [email protected]} */ public static final String USB_FUNCTION_MTP = "mtp"; /** * Name of the PTP USB function. * Used in extras for the [email protected] #ACTION_USB_STATE} broadcast * * [email protected]} */ public static final String USB_FUNCTION_PTP = "ptp"; /** * Name of the CHARGING USB function. * Used in extras for the [email protected] #ACTION_USB_STATE} broadcast * * [email protected]} */ public static final String USB_FUNCTION_CHARGING = "charging"; /** * Name of the audio source USB function. * Used in extras for the [email protected] #ACTION_USB_STATE} broadcast * * [email protected]} */ public static final String USB_FUNCTION_AUDIO_SOURCE = "audio_source"; /** * Name of the Accessory USB function. * Used in extras for the [email protected] #ACTION_USB_STATE} broadcast * * [email protected]} */ public static final String USB_FUNCTION_ACCESSORY = "accessory";这些是其定义。其中adb与charging不能同时兼容。
5、设置usb的流程是什么？
上层能够设定usb类型的类名叫做：UsbSettings，在其中，用户可以设定当前UsbSettings状态为mtp、ptp以及厂商定义的其他usb状态。
在用户操作时，会调用mUsbManager.setCurrentFunction(function, true);
tring function = USB_FUNCTION_DEFAULT; if (preference == mMtp && mMtp.isChecked()) { function = UsbManager.USB_FUNCTION_MTP; } else if (preference == mPtp && mPtp.isChecked()) { function = UsbManager.USB_FUNCTION_PTP; } else if (preference == mCharging && mCharging.isChecked()) { function = UsbManager.USB_FUNCTION_CHARGING; } else if (preference == mSDCard && mSDCard.isChecked()) { function = UsbManager.USB_FUNCTION_MASS_STORAGE; } operateInprogress = true; mUsbManager.setCurrentFunction(function, true); updateToggles(function);USBManager会继而调用UsbService的setCurrentFunctionUsbService.java
@Override public void setCurrentFunction(String function, boolean makeDefault) { mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null); // If attempt to change USB function while file transfer is restricted, ensure that // the current function is set to "none", and return. UserManager userManager = (UserManager) mContext.getSystemService(Context.USER_SERVICE); if (userManager.hasUserRestriction(UserManager.DISALLOW_USB_FILE_TRANSFER)) { if (mDeviceManager != null) mDeviceManager.setCurrentFunctions("none", false); return; } if (mDeviceManager != null) { mDeviceManager.setCurrentFunctions(function, makeDefault); } else { throw new IllegalStateException("USB device mode not supported"); } }最终还是会调用UsbDeviceManager中的setCurrentFunction。故剩余步骤可参考2.