when do FindBy attributes trigger a driver.FindElement?

Question

My question is: do webelements decorated with findby attributes call the findelement function upon each reference to them? If not, when?

And what is the procedure with List< webelement > which is also decorated? Does it trigger when you reference the list, or when you reference an element inside that list?

I'm asking because I have some situations where I'm getting stale element exceptions and I want to know how to deal with them.

Answer 1

WebElements are evaluated lazily. That is, if you never use a WebElement field in a PageObject, there will never be a call to "findElement" for it. Reference.

If don't want WebDriver to query the element each time, you have to use the @CacheLookup annotation.

What about the list part of my question?

The findElements is triggered when you query from the list. Say you have:

@FindBy(xpath = "//div[@class=\"langlist langlist-large\"]//a")
private List<WebElement> list;

Following code samples all trigger the findElements :

list.isEmpty();

WebElement element = list.get(0);

Where as

List<WebElement> newList = new ArrayList<WebElement>();
newList = list;

does not trigger the findElements().

Please check the LocatingElementListHandler class. I suggest diving into the source for answers.

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You may find this code comment from PageFactory class helpful:

/**
   * Instantiate an instance of the given class, and set a lazy proxy for each of the WebElement
   * and List<WebElement> fields that have been declared, assuming that the field name is also
   * the HTML element's "id" or "name". This means that for the class:
   * 
   * <code>
   * public class Page {
   *     private WebElement submit;
   * }
   * </code>
   * 
   * there will be an element that can be located using the xpath expression "//*[@id='submit']" or
   * "//*[@name='submit']"
   * 
   * By default, the element or the list is looked up each and every time a method is called upon it.
   * To change this behaviour, simply annotate the field with the {@link CacheLookup}.
   * To change how the element is located, use the {@link FindBy} annotation.
   * 
   * This method will attempt to instantiate the class given to it, preferably using a constructor
   * which takes a WebDriver instance as its only argument or falling back on a no-arg constructor.
   * An exception will be thrown if the class cannot be instantiated.
   * 
   * @see FindBy
   * @see CacheLookup
   * @param driver The driver that will be used to look up the elements
   * @param pageClassToProxy A class which will be initialised.
   * @return An instantiated instance of the class with WebElement and List<WebElement> fields proxied
   */