android.hardware.USB类介绍
在最新的Android版本中，android.hardware.USB是一个新增类，提供了USB相关事件的插拔，以及状态模式的广播。这里，可以看到USB连接、断开、是否为U盘、ADB模式等等。定义如下

public class Usb {
public static final String ACTION_USB_CONNECTED =
"android.hardware.action.USB_CONNECTED";

public static final String ACTION_USB_DISCONNECTED =
"android.hardware.action.USB_DISCONNECTED";

public static final String ACTION_USB_STATE =
"android.hardware.action.USB_STATE";

public static final String USB_CONNECTED = "connected";

public static final String USB_FUNCTION_MASS_STORAGE = "mass_storage";

public static final String USB_FUNCTION_ADB = "adb";

public static final String USB_FUNCTION_RNDIS = "rndis";

public static final String USB_FUNCTION_MTP = "mtp";

public static final String USB_FUNCTION_ENABLED = "enabled";

public static final String USB_FUNCTION_DISABLED = "disabled";