Java – Selenium 2.0 WebDriver: Element is no longer attached to the DOM error using Java

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I'm using the PageObject/PageFactory design pattern for my UI automation. Using Selenium 2.0 WebDriver, JAVA, I randomly get the error: org.openqa.selenium.StaleElementReferenceException: Element is no longer attached to the DOM, when I attempt logic like this:

@FindBy(how = HOW.ID, using = "item")
private List<WebElement> items

private void getItemThroughName(String name) {
    wait(items);

    for(int i = 0; i < items.size(); i++) {
        try {
            Thread.sleep(0500);
        } catch (InterruptedException e) { }

        this.wait(items);
        if(items.get(i).getText().contains(name)) {
            System.out.println("Found");
            break;
        }
    }
}

The error randomly happens at the if statement line, as you can see I've tried a couple things to avoid this, like sleeping a small amount of time, or waiting for the element again, neither works 100% of the time

Best Answer

First if you really have multiple elements on the by with the ID of "item" you should log a bug or talk to the developers on the site to fix that. An ID is meant to be unique.

As comments on the question already implied you should use an ExplicitWait in this case:

private void getItemThroughName(String name) {
    new WebDriverWait(driver, 30)
               .until(ExpectedConditions.presenceOfElementLocated(
                 By.xpath("id('item')[.='" + name + "']")
               ));
    // A timeout exception will be thrown otherwise
    System.out.println("Found");
}

How to use:

You can be sure that the function given above returns correct answer at the moment of time when it is called, but what about tracking element's visibility as an event?

Place the following code at the bottom of your <body> tag:

function onVisibilityChange(el, callback) {
    var old_visible;
    return function () {
        var visible = isElementInViewport(el);
        if (visible != old_visible) {
            old_visible = visible;
            if (typeof callback == 'function') {
                callback();
            }
        }
    }
}

var handler = onVisibilityChange(el, function() {
    /* Your code go here */
});


// jQuery
$(window).on('DOMContentLoaded load resize scroll', handler);

/* // Non-jQuery
if (window.addEventListener) {
    addEventListener('DOMContentLoaded', handler, false);
    addEventListener('load', handler, false);
    addEventListener('scroll', handler, false);
    addEventListener('resize', handler, false);
} else if (window.attachEvent)  {
    attachEvent('onDOMContentLoaded', handler); // Internet Explorer 9+ :(
    attachEvent('onload', handler);
    attachEvent('onscroll', handler);
    attachEvent('onresize', handler);
}
*/

If you do any DOM modifications, they can change your element's visibility of course.

Guidelines and common pitfalls:

Maybe you need to track page zoom / mobile device pinch? jQuery should handle zoom/pinch cross browser, otherwise first or second link should help you.

If you modify DOM, it can affect the element's visibility. You should take control over that and call handler() manually. Unfortunately, we don't have any cross browser onrepaint event. On the other hand that allows us to make optimizations and perform re-check only on DOM modifications that can change an element's visibility.

Never Ever use it inside jQuery $(document).ready() only, because there is no warranty CSS has been applied in this moment. Your code can work locally with your CSS on a hard drive, but once put on a remote server it will fail.

After DOMContentLoaded is fired, styles are applied, but the images are not loaded yet. So, we should add window.onload event listener.

We can't catch zoom/pinch event yet.

The last resort could be the following code:

/* TODO: this looks like a very bad code */
setInterval(handler, 600);

You can use the awesome feature pageVisibiliy of the HTML5 API if you care if the tab with your web page is active and visible.

TODO: this method does not handle two situations:

Overlapping using z-index.
Using overflow-scroll in element's container.
Try something new - The Intersection Observer API explained.

Javascript – Creating a new DOM element from an HTML string using built-in DOM methods or Prototype

Note: most current browsers support HTML <template> elements, which provide a more reliable way of turning creating elements from strings. See Mark Amery's answer below for details.

For older browsers, and node/jsdom: (which doesn't yet support <template> elements at the time of writing), use the following method. It's the same thing the libraries use to do to get DOM elements from an HTML string (with some extra work for IE to work around bugs with its implementation of innerHTML):

function createElementFromHTML(htmlString) {
  var div = document.createElement('div');
  div.innerHTML = htmlString.trim();

  // Change this to div.childNodes to support multiple top-level nodes
  return div.firstChild; 
}

Note that unlike HTML templates this won't work for some elements that cannot legally be children of a <div>, such as <td>s.

If you're already using a library, I would recommend you stick to the library-approved method of creating elements from HTML strings:

Prototype has this feature built-into its update() method.
jQuery has it implemented in its jQuery(html) and jQuery.parseHTML methods.

Best Answer

Related Solutions

Javascript – How to tell if a DOM element is visible in the current viewport

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Javascript – Creating a new DOM element from an HTML string using built-in DOM methods or Prototype

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