selenium学习：等待机制及实现.docx

Wait机制及实现Explicit and Implicit Waits（显示或隐式等待）Waiting is having the automated task execution elapse a certain amount of time before continuing with the next step. You should choose to use Explicit Waits or Implicit Waits.WARNING: Do not mix implicit and explicit waits. Doing so can cause unpredictable wait times. For example setting an implicit wait of 10s and an explicit wait of 15 seconds, could cause a timeout to occur after 20 seconds.Explicit WaitsAn 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.WebDriver driver = new FirefoxDriver();driver.get(http:/somedomain/url_that_delays_loading);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.Expected ConditionsThere are some common conditions that are frequently come across when automating web browsers. Listed below are Implementations of each. Java happens to have convienence methods so you dont have to code an ExpectedCondition class yourself or create your own utility package for them. Element is Clickable - it is Displayed and Enabled. WebDriverWait wait = new WebDriverWait(driver, 10); WebElement element = wait.until(ExpectedConditions.elementToBeClickable(By.id(someid);Implicit WaitsAn 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. WebDriver driver = new FirefoxDriver();driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);driver.get(http:/somedomain/url_that_delays_loading);WebElement myDynamicElement = driver.findElement(By.id(myDynamicElement);1显示等待：原理：显式等待,就是明确的要等到某个元素的出现或者是某个元素的可点击等条件,等不到,就一直等,除非在规定的时间之内都没找到,那么就跳出Exception.(简而言之：就是直到元素出现才去操作，如果超时则报异常)1.1 Java 线程等待函数 =硬等待Thread.sleep(int sleeptime);此方法会把当前的driver进程暂停一段时间，然后在执行接下来的操作。这方法有个缺点就是，你不能确定元素到底多久加载出来，如果你的sleepTimes是10秒，但是元素2秒就加载出来了，那么此进程还会继续等待8秒，造成时间浪费。所以非必要情况下不要使用此方法。1.2 显示智能等待写一个方法判断元素是不是已经加载出来public static void intelligentWait(WebDriver driver,int timeOut, final By by)try (new WebDriverWait(driver, timeOut).until(new ExpectedCondition() public Boolean apply(WebDriver driver) WebElement element = driver.findElement(by);return element.isDisplayed();); catch (TimeoutException e) Assert.fail(超时! + timeOut + 秒之后还没找到元素 + by + ,e);此方法有两个参数，timeOut是等待元素的超时时间，就是说过了这个时间如果元素还没加载出来就报错。By对象，这个是你元素的定位方式比如By.id(“login”);这个方法会在给定timeOut去查找元素，如果在小于timeOut的时间内找到了元素，剩下的时间不在等待，直接执行接下来的操作。Main方法中验证public static void main(String args) throws InterruptedException WebDriver driver = new FirefoxDriver();/设置等待页面完全加载的时间是10秒，如果在10秒内加载完毕，剩余时间不在等待driver.manage().timeouts().pageLoadTimeout(10, TimeUnit.SECONDS);driver.get(/);By inputBox = By.id(kw);By searchButton = By.id(su);/智能等待元素加载出来intelligentWait(driver, 10, inputBox);/智能等待元素加载出来intelligentWait(driver, 10, searchButton);/输入内容driver.findElement(inputBox).sendKeys(JAVA);/点击查询driver.findElement(searchButton).click();driver.quit();具体见Java文件：2隐式等待/driver.manage().timeouts().pageLoadTimeout(pageLoadTime, TimeUnit.SECONDS);driver.manage().timeouts().implicitlyWait(second, TimeUnit.SECONDS);这段代码，加载driver.get(url)方法之前，他们等待你给定的时间，如果在给定时间内网页还是没有加载出来就会报错