selenium之ExpectedConditions类

API中对于该类的介绍：Canned ExpectedConditions which are generally useful within webdriver tests。很笼统，大概意思就是在webdriver的测试中会有用，那到底有什么用呢，下面我们就来一探究竟。

该类没有构造函数，所有的方法都是静态的，所以我们可以直接用类名调用，我只介绍里面几个方法，其它方法的用法都类似，具体查api

• 1.alertIsPresent()判断alert弹框出现了没，返回值是ExpectedCondition<Alert>，我们可以这样用

•     public void testalertIsPresent() {
  
          dr.findElement(By.id("alert")).findElement(By.className("alert")).click();
          ExpectedCondition<Alert> e = ExpectedConditions.alertIsPresent();
          Alert alert = e.apply(dr);
          alert.accept();
      }

  也可以这样用

      public void testalertIsPresentW() {
          WebDriverWait wait = new WebDriverWait(dr,10);
          dr.findElement(By.id("alert")).findElement(By.className("alert")).click();
          ExpectedCondition<Alert> e = ExpectedConditions.alertIsPresent();
          Alert alert = wait.until(e);
          alert.accept();
      }

  apply用了com.google.common.base.Function的方法，而until用了FluentWait的方法。那么这两者有和区别呢，通过下面这个例子介绍，

• 2. textToBePresentInElementLocated()：文本是否出现在所定位的元素中

•     public void testtextToBePresentInElementLocated() {
          WebDriverWait wait = new WebDriverWait(dr,10);
          dr.findElement(By.className("wait")).click();
          ExpectedCondition<Boolean> e1 = ExpectedConditions.textToBePresentInElementLocated(By.className("red"),"wait for display");
          System.out.println(e1.apply(dr));//false
          //System.out.println(wait.until(e1));    //报true
  
      }

  apply不会去等待所找元素是否存在，直接false报错no such elment。而until会在等待10秒，如果出现则返回true，否则超时。

• 3.visibilityOfElementLocated()，该方法是判断定位的元素是否存在，使用的方法时（），apply也会去等待

  public void testvisibilityOfElementLocated() {
          WebDriverWait wait = new WebDriverWait(dr,10);
          dr.findElement(By.className("wait")).click();
          ExpectedCondition<WebElement> e1 = ExpectedConditions.visibilityOfElementLocated(By.className("red"));
  
          System.out.println(wait.until(e1).getText());    //wait for display
          System.out.println(e1.apply(dr).getText());    //wait for display
  
      }

• 4.visibilityOf()，判断元素是否可见

      public void testvisibilityOf() {
          WebDriverWait wait = new WebDriverWait(dr,10);
          ExpectedCondition<WebElement> e1 = ExpectedConditions.visibilityOf(dr.findElement(By.className("wait")));
  
          System.out.println(e1.apply(dr).getAttribute("value"));    //wait
          //System.out.println(wait.until(e1).getAttribute("value"));//wait
      }

5.visibilityOfElementLocated()，定位的元素是否可见

    public void testvisibilityOfElementLocated() {
        WebDriverWait wait = new WebDriverWait(dr,10);
        dr.findElement(By.className("wait")).click();
        ExpectedCondition<WebElement> e1 = ExpectedConditions.visibilityOfElementLocated(By.className("red"));

        System.out.println(wait.until(e1).getText());    //wait for display
        System.out.println(e1.apply(dr).getText());    //wait for display

    }

以上列举了TestExpectedConditions的用法，鉴于apply会存在失败的情况，建议使用until。

PS：小插曲

下面的例子是api中关于FluentWait的用法

Sample usage:

   // Waiting 30 seconds for an element to be present on the page, checking
   // for its presence once every 5 seconds.
   Wait<WebDriver> wait = new FluentWait<WebDriver>(driver)
       .withTimeout(30, SECONDS)
       .pollingEvery(5, SECONDS)
       .ignoring(NoSuchElementException.class);

   WebElement foo = wait.until(new Function<WebDriver, WebElement>() {
     public WebElement apply(WebDriver driver) {
       return driver.findElement(By.id("foo"));
     }
   });

详细用法：

    @Test(enabled=false)
    public void testuntilWebElement() {
        WebDriverWait wait = new WebDriverWait(dr,10);
        WebElement we = wait.until(new ExpectedCondition<WebElement>(){
            @Override
            public WebElement apply(WebDriver arg0) {
                // TODO Auto-generated method stub
                return arg0.findElement(By.id("user"));
            }}) ;
        we.sendKeys("test");
    }

    @Test(enabled=false)
    public void testuntilBoolean() {
        WebDriverWait wait = new WebDriverWait(dr,10);
        boolean we = wait.until(new ExpectedCondition<WebElement>(){
            @Override
            public WebElement apply(WebDriver arg0) {
                // TODO Auto-generated method stub
                return arg0.findElement(By.id("user"));
            }}).isDisplayed();
        System.out.println(we);
    }

两者用法目的差不多，可以根据具体情况选择使用哪种方式。

文中所用到的html例子：

http://pan.baidu.com/s/1i3jjo3b