Page History

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Let's review a simple example. Here's a portion of the template for a page (let's call it "Chooser") that lets the user choose a number between 1 and 10:

<p> Choose a number from 1 to 10:

    <t:count end="10" value="index">
        <a t:id="select" t:type="actionlink" context="index">${index}</t:comp>
    </t:count>
</p>

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When a component event occurs, Tapestry invokes any event handler methods that you have identified for that event. You can identify your event handler methods via a naming convention (see Method Naming Convention below), or via the @OnEvent annotation.

  @OnEvent(component = "select")
  void valueChosen(int value)
  {
    this.value = value;
  }

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For some components, more than one type of event can occur, in which case you will want to be more specific:

  @OnEvent(value = "action", component = "select")
  void valueChosen(int value)
  {
    this.value = value;
  }

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The previous example may be rewritten as:

  void onActionFromSelect(int value)
  {
    this.value = value;
  }

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In other words, there's no need to do this:

  void onActionFromRunQuery()
  {
    try
    {
      dao.executeQuery();
    }
    catch (JDBCException ex)
    {
      throw new RuntimeException(ex);
    }
  }

Instead, you may simply say:

  void onActionFromRunQuery() throws JDBCException
  {
    dao.executeQuery();
  }

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Tapestry emits a new event, of type "exception", passing the thrown exception as the context. In fact, the exception is wrapped inside a ComponentEventException, from which you may extract the event type and context.

Thus:

  Object onException(Throwable cause)
  {
    message = cause.getMessage();

    return this;
  }

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