SoftKeyboardEvent & StageWebView

SoftKeyboardEvent of the form can not be acquired in the StageWebView. How do I

  stageWebView = new StageWebView();

  stageWebView.stage = stage;

  var view_rect: Rectangle = new Rectangle();

  view_rect.x = 0;

  view_rect.y = 0;

  view_rect.width = 480;

  view_rect.height = 700;

  stageWebView.viewPort = view_rect;

  stageWebView.loadURL("https://www.google.com");

  stageWebView.addEventListener(SoftKeyboardEvent.SOFT_KEYBOARD_ACTIVATING, activating);

  stageWebView.addEventListener(SoftKeyboardEvent.SOFT_KEYBOARD_ACTIVATE, activate);

  stageWebView.addEventListener(SoftKeyboardEvent.SOFT_KEYBOARD_DEACTIVATE, deactivate);

  function activating( event:SoftKeyboardEvent ):void  {

  }

  function activate( event:SoftKeyboardEvent ):void  {

  }

  function deactivate( event:SoftKeyboardEvent ):void  {

  }