使用 Java 的 Selenium WebDriver 测试中的 waitForVisible/waitForElementPresent 是否等效？

Question

With "HTML" Selenium tests (created with Selenium IDE or manually), you can use some very handy commands like WaitForElementPresent or WaitForVisible .

<tr>
    <td>waitForElementPresent</td>
    <td>id=saveButton</td>
    <td></td>
</tr>

When coding Selenium tests in Java (Webdriver / Selenium RC—I'm not sure of the terminology here), is there something similar built-in ?

For example, for checking that a dialog (that takes a while to open) is visible...

WebElement dialog = driver.findElement(By.id("reportDialog"));
assertTrue(dialog.isDisplayed());  // often fails as it isn't visible *yet*

What's the cleanest robust way to code such check?

Adding Thread.sleep() calls all over the place would be ugly and fragile, and rolling your own while loops seems pretty clumsy too...

Answer 1

Implicit and Explicit Waits

Implicit Wait

An implicit wait is to tell WebDriver to poll the DOM for a certain amount of time when trying to find an element or elements if they are not immediately available. The default setting is 0. Once set, the implicit wait is set for the life of the WebDriver object instance.

driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);

Explicit Wait + Expected Conditions

An explicit waits is code you define to wait for a certain condition to occur before proceeding further in the code. The worst case of this is Thread.sleep(), which sets the condition to an exact time period to wait. There are some convenience methods provided that help you write code that will wait only as long as required. WebDriverWait in combination with ExpectedCondition is one way this can be accomplished.

WebDriverWait wait = new WebDriverWait(driver, 10);
WebElement element = wait.until(
        ExpectedConditions.visibilityOfElementLocated(By.id("someid")));

Answer 2

WebElement myDynamicElement = (new WebDriverWait(driver, 10))
.until(ExpectedConditions.presenceOfElementLocated(By.id("myDynamicElement")));

This waits up to 10 seconds before throwing a TimeoutException or if it finds the element will return it in 0 - 10 seconds. WebDriverWait by default calls the ExpectedCondition every 500 milliseconds until it returns successfully. A successful return is for ExpectedCondition type is Boolean return true or not null return value for all other ExpectedCondition types.

---

WebDriverWait wait = new WebDriverWait(driver, 10);
WebElement element = wait.until(ExpectedConditions.elementToBeClickable(By.id("someid")));

Element is Clickable - it is Displayed and Enabled.

From WebDriver docs: Explicit and Implicit Waits

Answer 3

Well the thing is that you probably actually don't want the test to run indefinitely. You just want to wait a longer amount of time before the library decides the element doesn't exist. In that case, the most elegant solution is to use implicit wait, which is designed for just that:

driver.manage().timeouts().implicitlyWait( ... )

Answer 4

Another way to wait for maximum of certain amount say 10 seconds of time for the element to be displayed as below:

(new WebDriverWait(driver, 10)).until(new ExpectedCondition<Boolean>() {
            public Boolean apply(WebDriver d) {
                return d.findElement(By.id("<name>")).isDisplayed();

            }
        });

Answer 5

public static boolean waitForUntilVisible(WebDriver driver, Integer time, By by ) {
    WebDriverWait wait = new WebDriverWait(driver,  Duration.ofSeconds(time));

    try {
        wait.until( ExpectedConditions.presenceOfElementLocated(by) ); 
    }catch(NoSuchElementException e) {
        return false;
    }catch (TimeoutException e) {
        return false;
    }
    return true;
}

Answer 6

For individual element the code below could be used:

private boolean isElementPresent(By by) {
        try {
            driver.findElement(by);
            return true;
        } catch (NoSuchElementException e) {
            return false;
        }
    }
for (int second = 0;; second++) {
            if (second >= 60){
                fail("timeout");
            }
            try {
                if (isElementPresent(By.id("someid"))){
                    break;
                }
                }
            catch (Exception e) {

            }
            Thread.sleep(1000);
        }