Native implementation associated with {@link com.google.gwt.user.client.History}. User classes should not use this class directly.

This base version uses the HTML5 standard window.onhashchange event to determine when the URL hash identifier changes.

class HistoryImpl implements HasValueChangeHandlers<String> {

 static String _token = "";

 static String getToken() {
   return (_token == null) ? "" : _token;
 }

 static void setToken(String token) {
   HistoryImpl._token = token;
 }

 EventBus _handlers = new SimpleEventBus();

 //*****************************************
 // Implementation of HasValueChangeHandlers
 //*****************************************

 /**
  * Adds a {@link ValueChangeEvent} handler to be informed of changes to the
  * browser's history stack.
  *
  * @param handler the handler
  */
 HandlerRegistration addValueChangeHandler(ValueChangeHandler<String> handler) {
   return _handlers.addHandler(ValueChangeEvent.TYPE, handler);
 }

 //****

 String encodeFragment(String fragment) {
   // encodeURI() does *not* encode the '#' character.
   return fragment; //encodeURI(fragment).replace("#", "%23");
 }

 String decodeFragment(String encodedFragment) {
   // decodeURI() does *not* decode the '#' character.
   return encodedFragment; //decodeURI(encodedFragment.replace("%23", "#"));
 }

 void fireEvent(DwtEvent event) {
   _handlers.fireEvent(event);
 }

 /**
  * Fires the {@link ValueChangeEvent} to all handlers with the given tokens.
  */
 void fireHistoryChangedImpl(String newToken) {
   ValueChangeEvent.fire(this, newToken);
 }

 EventBus getHandlers() {
   return _handlers;
 }

 bool init() {

   var token = '';

   // Get the initial token from the url's hash component.
   String hash = dart_html.window.location.hash;
   if (hash.length > 0) {
     token = decodeFragment(hash.substring(1));
   }

   HistoryImpl.setToken(token);

   //var historyImpl = this;

   //var oldHandler = dart_html.window.on["hashchange"];

   dart_html.window.onHashChange.listen((dart_html.Event event) {
     var token = '';
     String hash = dart_html.window.location.hash;
     if (hash.length > 0) {
       token = decodeFragment(hash.substring(1));
     }

     newItemOnEvent(token);

//      if (oldHandler) {
//        oldHandler();
//      }
   });

   return true;

 }

 void newItem(String historyToken, bool issueEvent) {
   historyToken = (historyToken == null) ? "" : historyToken;
   if (historyToken != getToken()) {
     setToken(historyToken);
     nativeUpdate(historyToken);
     if (issueEvent) {
       fireHistoryChangedImpl(historyToken);
     }
   }
 }

 void newItemOnEvent(String historyToken) {
   historyToken = (historyToken == null) ? "" : historyToken;
   if (historyToken != getToken()) {
     setToken(historyToken);
     nativeUpdateOnEvent(historyToken);
     fireHistoryChangedImpl(historyToken);
   }
 }

 void nativeUpdate(String historyToken) {
   //$wnd.location.hash = this.@com.google.gwt.user.client.impl.HistoryImpl::encodeFragment(Ljava/lang/String;)(historyToken);
   dart_html.window.location.hash = encodeFragment(historyToken);
 }

 void nativeUpdateOnEvent(String historyToken) {
   // Do nothing, the hash is already updated.
 }
}