Selenium Expected Conditions, where does the instance of Webdriver come from?

Question

I am struggling to figure out how the WebDriver instance is passed to Selenium's expected conditions.

So I have a simple WebDriverWait for the visibility of a web element:

new WebDriverWait(webDriver, Configuration.WEB_DRIVER_WAIT_TIMEOUT)
                .until(ExpectedConditions.visibilityOf(element));

The webDriver instance here is a chromedriver which has been instantiated above.

My question is: in the method visibilityOf():

public static ExpectedCondition<WebElement> visibilityOf(final WebElement element) {
    return new ExpectedCondition<WebElement>() {
      @Override
      public WebElement apply(WebDriver driver) {
        return elementIfVisible(element);
      }

      @Override
      public String toString() {
        return "visibility of " + element;
      }
    };
  }

Just above, how and which instance of WebDriver gets passed to the apply()? I understand that the ExpectedCondition implements the Function Interface

public interface ExpectedCondition<T> extends Function<WebDriver, T> {}

which takes as first argument WebDriver.

How the instance of the WebDriver gets passed to ExpectedCondition of the visibilytOf()?

Thanks

Answer 1

When you are creating the WebDriverWait you are passing the webdriver instance. The same instance will be passed to the apply method of the functional interface of ExpectedCondition by the until method.

WebDriverWait extends FluentWait<WebDriver> which actually implements the until method. When you construct the WebDriverWait the driver is passed as a parameter to FluentWait which keeps it in a attribute.

Now when you call until on WebDriverWait the until method calls the apply method passing the driver you actually passed to the constructor. The ExpectedCondition object that you are constructing in-effect receives two inputs. The WebElement you are passing to it as well as the driver that you pass to WebDriverWait.

The source code is not too complicated - you can have a look at it for finer details :)