How to return a lazily-instantiated dynamic webelement

Question

I've been using @FindBy for a while now, and I love the fact that the element doesn't get located until its necessary (not on instantiation).

However, the webpage may have anywhere from 2-10 of a certain element, and the id's on the elements are numbered (so the first element has an id of "element1" and so forth)

I would like to write a function where I can pass in an integer, and it will return a WebElement with the appropriate ID, AND is lazily instantiated. That means having a function like the following won't work:

public WebElement getElement(int numOnPage){
    return driver.findElement(By.id("element"+numOnPage));
}

Because the instant I call that function the WebElement gets located. (The reason why it can't be instantiated is because I have a function that waits until it the element exists by calling isDisplayed() over and over on it, catching NoSuchElementExceptions).

I also realize that I could create a List<WebElement> that selects via CSS every element whose ID starts with "element" but I have had other cases where I've wanted to return a dynamically generated element, and had to use a workaround there as well.

Thanks!

score 1 · Accepted Answer · answered Aug 04 '13 at 05:26

First, I don't really understand why you absolutely need to get a WebElement reference before the element is really in the page. In a normal case, you could check that the page is completely loaded and then find for a WebElement. First would be typically done with a loop and a catch for NoSuchElementException as you mentioned.

However, if you need a reference for a WebElement before it can't be found in the page, I would simply create a proxy which loads lazily (only when first time needed) the real WebElement instance. Something like this:

public WebElement getElement(final int numOnPage) {
        return (WebElement) Proxy.newProxyInstance(this.getClass().getClassLoader(), new Class<?>[] { WebElement.class }, new InvocationHandler() {
            // Lazy initialized instance of WebElement
            private WebElement webElement;

            public Object invoke(Object proxy, Method method, Object[] args)
                    throws Throwable {
                if (webElement == null) {
                    webElement = driver.findElement(By.id("element" + numOnPage));
                }
                return method.invoke(webElement, args);
            }
        });
    }

By calling getElement, you retrieve an object of type WebElement. As soon as you call one of its method, it will be retrieved using WebDriver.findElement. Note that, if you call a method on the proxy instance, the element must be in the page otherwise you get of course a NoSuchElementException.

The cause was that I have a function where I call isDisplayed() (with a try/catch) over and over...but if I pass in the element returned from getElement(), and the element doesn't exist yet, getElement() will throw the exception before it ever hits the function that is waiting for it to exist. Thank you! — Nathan Merrill, Aug 05 '13 at 17:00

score 1 · Answer 2 · answered Aug 04 '13 at 09:37

If i'm understanding the question correctly, you can't do this with the @FindBy annotation. The problem is that Annotations in Java are processed during compile time and as a consequence you cannot modify them on the fly:

http://docs.oracle.com/javase/tutorial/java/annotations/

It does however sound like your problem could be easily fixed by using an explicit wait:

public WebElement getElement(int numOnPage){
    WebDriverWait waiting= new WebDriverWait(driver, 15, 100);
    return waiting.until(ExpectedConditions.visibilityOfElementLocated(By.id("element"+numOnPage)));
}

This would scan the page waiting for the element to exist and be visible and when it is return a WebElement to you.

How to return a lazily-instantiated dynamic webelement

2 Answers2

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