I've initialized all the WebElements in the project using PageFactory. For logging purpose I am trimming the logs of the elements. But I faced some difficulty while trimming. So when I tried to print the elements, I found that most of the times an element is printed in this manner:
[[ChromeDriver: chrome on XP (d96cf99661f5d938b75f8448dad62d3b)] -> xpath: //button[#ng-reflect-label='Add']]
but in extremely minor cases, it is printed this way:
Proxy element for: DefaultElementLocator 'By.xpath: //div[contains(#class,'ui-growl-icon-close')]'
My trimming method looks for "->" in the element so most of the times it works, but rarely it fails when it changes to "Proxy element for..."
Thing is there is no consistency in the elements when they get printed. Element getting printed as "Proxy element for..." would get printed as "[[ChromeDriver.." in the next iteration
Browser used: chrome (only)
When you use PageFactory for initializing webelement it initializes it with a Proxy object. Only when you access the element from your code, like a sendkeys, is the actual webelement retrieved and initialized fully.
For a code level discussion of how selenium pagefactory initializes refer to this. http://www.alechenninger.com/2014/07/a-case-study-of-javas-dynamic-proxies_14.html
Related
Hi I am looking for an explanation on how selenium searches for an element on a website. For us, we use inspect element to find the id, name, xpath, etc. of an element, and then put it in selenium for some action to be done. How does selenium find the element we tell it to find? Does it ctrl shift J like us and inspect element?
Note: I am not looking for how to code selenium to find element.
Html pages are just documents with elements structured like in a tree.
In general
Selenium uses element locators to find things. Locators work lazily. When you look up an element Selenium first checks if its cached. If not, it uses SearchContext which finds all elements within the current context (eg. DOM element) using a given mechanism, for example by XPathEvaluator.
SearchContext runs findElement() if you are looking for one element or findElements() if you are looking for more than one.
In simple terms, findElement() tries to run JavaScript script to find the element asynchronously. If it can’t, it tries to find it directly by using an interestingly called method – xpathWizardry, i.e. by using XPathEvaluator evaluation.
XPath
When you use XPath (XML Path Language) in Selenium, this is just a way to navigate through hierarchical structure of an XML-like document, such as html.
XPath uses a non-XML syntax to provide a flexible way of pointing to different parts of an XML document.
Internally selenium uses W3 XPathEvaluator, which evaluates XPath expressions.
You can study XPathEvaluator source code here.
Search Context
The SearchContext is a topmost interface present in the Selenium WebDriver hierarchy. It has two methods that will be the abstract as SearchContext is an interface.
findElement(): Find the first WebElement using the given method.
WebElement findElement(By by)
Parameters:
by - The locating mechanism
Returns:
The first matching element on the current context
Throws:
NoSuchElementException - If no matching elements are found
findElements(): Find all elements within the current context using the given mechanism.
java.util.List<WebElement> findElements(By by)
Parameters:
by - The locating mechanism to use
Returns:
A list of all WebElements, or an empty list if nothing matches
The browser DOM exposes API like querySelector,querySelectorAll, getElementById, getElementsByClassName, getElementsByName, etc through javascript that can be used to locate elements.
For example :
Navigate to www.bing.com
Press F12 to open developer console.
Enter document.querySelector("#sb_form_q") to locate search box input by css selector. I am using #Id here as css selector.
Enter document.getElementById("sb_form_q") to locate search box input by it's Id
Enter document.getElementsByClassName("sb_form_q")[0] to locate search box input by it's class name
Enter document.getElementsByName("q")[0] to locate search box input by it's name
All of above should return "<input id="sb_form_q" class="sb_form_q" name="q" type="search" maxlength="1000" autocomplete="off" aria-label="Enter your search term" autofocus="" aria-controls="sw_as" aria-autocomplete="both" aria-owns="sw_as" aria-activedescendant="sa_5004">" same result.
Selenium uses these DOM API to retrieve the elements. However, selenium might use these DOM API via some other mechanism (e.g C ++) and not by executing javascript for faster execution. XPath lookup is something not supported directly by browser DOM API. Selenium probably provides it's own implementation for XPath lookup or rely on some browser polyfill for this functionality.
I am trying to learn the PageFactory model. I understood the fact that when we do a initElements, the WebElements are located. Say for example, I click on a webelement and because of which there is a change in one of the other webelements in DOM. Now, obviously I would get a StaleElementReferenceException here. How would I resolve this issue?
Should I find that specific WebElement again knowing the fact that there can be a change in the WebElement's properties in the DOM? or is there an another way to handle this?
StaleElementReferenceException
StaleElementReferenceException extends WebDriverException and indicates that the previous reference of the element is now stale and the element reference is no longer present on the DOM of the page.
Common Reasons
The common reasons behind facing StaleElementReferenceException are as follows:
The element has been deleted entirely.
The element is no longer attached to the DOM.
The webpage on which the element was part of has been refreshed.
The (previous) element has been deleted by a JavaScript or AjaxCall and is replaced by a (new) element with the same ID or other attributes.
Solution : If an (old) element has been replaced with new identical one, the simple strategy would be to use findElement() or findElements to look out for the element again.
Answering your queries
When we do a initElements, the WebElements are located : When you call initElements() method, all the WebElements of that page will get initialized. For example,
LoginPageNew login_page = PageFactory.initElements(driver, LoginPageNew.class);
This line of code will initialize all the static WebElements defined within the scope of the LoginPageNew.class whenever and wherever it is invoked from your Automation Script.
I click on a webelement and because of which there is a change in one of the other webelements in DOM : This is pretty much possible.
As an example, in general invoking click() on a <input> tag wouldn't trigger any change of any of the WebElements on the HTML DOM.
Where as invoking click() on a <button> tag or <a> tag may call a JavaScript or a Ajax which inturn may delete an element or can replace the (previous) element by a (new) element with the same ID or other attributes.
Conclusion
So, if WebDriver throws a StaleElementReferenceException, that implies even though the element still exists, the reference is lost. We should discard the current reference we have and replace it by locating the WebElement once again when it gets attached to the DOM. That means you have to again reinitialize the class through initElements() method which inturn reinitializes all the WebElements defined in that page.
Solution
If a old element has been replaced with new identical one, the simple strategy would be to invoke WebDriverWait inconjunction with ExpectedConditions to look out for the element.
You can find relevant detailed discussions in:
How to add explicit wait in PageFactory in PageObjectModel?
References
Here are the references of this discussion:
Stale Element Reference Exception
Class StaleElementReferenceException
Selenium: How to tell if RemoteWebDriver.findElements(By) can throw StaleElementReferenceException at all?
This is a known problem with the PageFactory implementation.
If you are unlucky enough for the element to become stale in the instant between the element being found, and then the element being clicked upon, you will get this error. Unfortunately the PageFactory code does not try to find the element again if it has become stale and it throws an Exception.
I would classify this as a bug with PageFactory, it should auto re-find the element if it ever becomes stale (unless the #CacheLookup annotation is used).
The suggestion to recall initElements isn't going to fix anything, you only need to init the elements once because that binds a Java proxy class to the element in question. The page factory implementation is supposed to remove the possibility of StaleElementReferenceExceptions (hence why this is a bug)
Stale element exception is thrown in two cases
The element is no longer attached to the DOM.
The element has been deleted entirely.
When this happen you wrap your code in try catch block then you can loop and retry as many times as you need until it succeeds.
public void waitForElementPresent(final By by, int timeout){
WebDriverWait wait = (WebDriverWait)new WebDriverWait(driver,timeout)
.ignoring(StaleElementReferenceException.class);
wait.until(new ExpectedCondition<Boolean>(){
#Override
public Boolean apply(WebDriver webDriver) {
WebElement element = webDriver.findElement(by);
return element != null && element.isDisplayed();
}
});
}
why this comes occasionally in selenium java, when I print the element I found
Proxy element for: DefaultElementLocator 'By.xpath:
when I print other elements usually like this
[ChromeDriver: chrome on XP (25f238cd0f65e6332256868f1675519e)]
these proxy element consumes time also
Proxy elements are ones defined using PageFactory
The default element locator, which will lazily locate an element or an element list on a page. This class is designed for use with the PageFactory and understands the annotations FindBy and CacheLookup. If you take off PageFactory from your script or from code evaluation during debug time, the problem will be solved
I got stuck not just for this one case. Many cases came out with nosuchelement exception, I cannot find the reason why. I use chrome console to locate the element and it shows correct result. Is that possible something wrong with the page itself, not my script?
Context click on the element you are trying to click, and see if the element is inside any frame. Try to navigate through the tags and see if this element is under any iframe.
switch to the iframe using,
driver.switchTo().frame(driver.findElement(By.xpath("iframexpath")));
I had a question . When i "inspect" this particular element and take "exact" xpath and copy it to my selenium script and run my script, it fails to identify?
Any idea how to do it?
Repeating again, i copied the exact xpath , tried inspecting element. All correct. Still :(
Thanks,
S.K
If Selenium fails to find an element you know is present, commonly the problem is with synchronization: Selenium tries to access the element too fast, before it appears on the page (and when you try to inspect element even a second later, you can see it, since it was rendered by then). Try to WAIT for the very same element before doing anything else. Examples of the wait can be found here