我正在尝试在Selenium Web驱动程序脚本下执行，但是org.openqa.selenium.ElementNotVisibleException: Element is not currently visible and so may not be interacted with几次（并非所有时间）都出现错误。有时在循环中第一次迭代，有时在2次迭代中，有时没有启动循环。它打印所有可用项目的计数正确，但是乳清试图单击项目，显示Element is not currently visible...

public void pickitems() throws Exception  
        {
        Webdriver driver = new firefoxdriver();
        driver.get("http://www.bigbasket.com");
        driver.manage().window().maximize();
            //Selecting Location
        List<WebElement> list = driver.findElement(By.id("ftv-city-popup")).findElements(By.tagName("button"));
        int location = r.nextInt(list.size());
        list.get(location).click();
            //Selection random Category from left panel through list 
        Thread.sleep(30000);
        List<WebElement> xyz = driver.findElement(By.id("uiv2-main-menu")).findElements(By.className("top-category"));
        System.out.println(xyz.size());
        Random r = new Random();
        int category = r.nextInt(xyz.size());
        xyz.get(category).click();


        for (int i = 0; i < 3; i++) {
            Thread.sleep(30000);
            List<WebElement> availableItems = driver.findElements(By.cssSelector("a.uiv2-add-button.a2c"));
            System.out.println(availableItems.size());
            if (availableItems.size() > 0)
            {
                int selectItem = r.nextInt(availableItems.size());
                availableItems.get(selectItem).click();

            } 
            else
            {
                Thread.sleep(30000);
                List<WebElement> availableItems2 = driver.findElements(By.cssSelector("a.uiv2-add-button.a2c"));
                if (availableItems2.size() == 0) {
                    System.out.println("No more items are available. Sorry for the inconvenience");
                }
                else {
                    Assert.fail("Unable to select items. May be page loading issue");
                }


            }

        }

  }

}