Android:帮我详细讲解一下这段代码

private void clearPackagePreferredActivities(Context context, String packageName) {
 PackageManager mPm = context.getPackageManager();
 UserManager mUserManager = (UserManager)context.getSystemService(Context.USER_SERVICE);
 AppWidgetManager mAppWidgetManager = AppWidgetManager.getInstance(context);;
 IBinder b = ServiceManager.getService(Context.USB_SERVICE);
 IUsbManager mUsbManager = IUsbManager.Stub.asInterface(b);
 if (mUsbManager != null) {
 mPm.clearPackagePreferredActivities(packageName);
 try {
 mUsbManager.clearDefaults(packageName, UserHandle.myUserId());
 } catch (Exception e) {
 }
 }
 }