What is the reason for the History.newItem(token) to invoke the onvaluechange(...) by default

Hello,

For example take the example in the documentation:

https://developers.google.com/web-toolkit/doc/latest/DevGuideCodingBasicsHistory 

In short, it is a tab panel with 3 tabs, and history functionality is added so you can use back and forth browser buttons to navigate to previous/next tab.

I'll focus on the following 2 parts of the code:

1. adding corresponding token to history stack when pressing opening a tab

tabPanel.addSelectionHandler(new SelectionHandler<Integer>(){
      public void onSelection(SelectionEvent<Integer> event) {
        History.newItem("page" + event.getSelectedItem());
      }});

2. When back and forward button is clicked navigate to the correct tab:

public void onValueChange(ValueChangeEvent<String> event) {
        String historyToken = event.getValue();

        // Parse the history token
        try {
          if (historyToken.substring(0, 4).equals("page")) {
            String tabIndexToken = historyToken.substring(4, 5);
            int tabIndex = Integer.parseInt(tabIndexToken);
            // Select the specified tab panel
            tabPanel.selectTab(tabIndex);
          } else {
            tabPanel.selectTab(0);
          }

        } catch (IndexOutOfBoundsException e) {
          tabPanel.selectTab(0);
        }
      }

And here comes the question again: Why when i push a history token on the stack (when opening a tab), is the "onvaluechange" operation triggered.

It seems unnecessary to me. The tab is opened because you click it's title, and then it is opened again because of the onvalueChange operation.

I'm aware of the History.newItem(token, false) operation - which i am currently using -  to avoid calling the onvaluechange() operation, but why is this not default behavior, I just don't see why you would need to call that operation.

Your thoughts are very appreciated :)

Regards,

Ruben

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