webdriver org.openqa.selenium.NoSuchElementException：无法找到元素：

Question

What I'm trying to do is checking elements on each page, if visible and if it is visible on current page i would like to make some assertion. My code looks like below:

package com.example.tests;

import java.util.Iterator;
import java.util.List;
import java.util.regex.Pattern;
import java.util.concurrent.TimeUnit;

import org.junit.*;

import static org.junit.Assert.*;
import static org.hamcrest.CoreMatchers.*;

import org.openqa.selenium.*;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.openqa.selenium.support.ui.Select;

import com.thoughtworks.selenium.Selenium;
import com.thoughtworks.selenium.webdriven.WebDriverBackedSelenium;

public class Webdriver_class {
  private WebDriver driver;
  private String baseUrl;
  private boolean acceptNextAlert = true;
  private StringBuffer verificationErrors = new StringBuffer();

  @Before
  public void setUp() throws Exception {
    driver = new FirefoxDriver();
    baseUrl = "http://www.lotto.pl/";
    driver.manage().timeouts().implicitlyWait(30, TimeUnit.SECONDS);
  }

  @Test
  public void testUntitled() throws Exception {
    driver.get(baseUrl + "/lotto/wyniki-i-wygrane/wygrane");
    assertEquals("Wyniki i wygrane Lotto i Lotto Plus | Lotto, Kaskada, Multi Multi, Mini Lotto, Joker, Zdrapki - lotto.pl", driver.getTitle());
    assertEquals("28-07-11", driver.findElement(By.xpath("//div[@id='page']/div[3]/div[2]/div[2]/table/tbody/tr[77]/td[5]")).getText());

    ///number of pages///
    String xpath = "html/body/div[3]/div[1]/div/div[3]/div[2]/div[2]/div[3]/div/ul/li";
    List<WebElement> elements = driver.findElements(By.xpath(xpath));
    int x=elements.size();
    System.out.println("liczba stron = "+elements.size());

    ////end//////


   for(int i=1; i<=x; i++){ 


            if(driver.findElement(By.xpath("//div[@id='page']/div[3]/div[2]/div[2]/table/tbody/tr[contains(td[3],'Warszawa') and contains (td[5],'21-02-09')]/td[1]")) != null)

              { assertEquals("100.", driver.findElement(By.xpath("//div[@id='page']/div[3]/div[2]/div[2]/table/tbody/tr[contains(td[3],'Warszawa') and contains (td[5],'21-02-09')]/td[1]")).getText());
               assertEquals("100.", driver.findElement(By.xpath("//div[@id='page']/div[3]/div[2]/div[2]/table/tbody/tr[contains(td[3],'Warszawa') and contains (td[5],'21-02-09')]/td[1]")).getText());
             };

            if(driver.findElement(By.xpath("//div[@id='page']/div[3]/div[2]/div[2]/table/tbody/tr[contains(td[3],'Nowa Sól') and contains (td[5],'05-04-12')]/td[1]")) != null)
            { assertEquals("99.", driver.findElement(By.xpath("//div[@id='page']/div[3]/div[2]/div[2]/table/tbody/tr[contains(td[3],'Nowa Sól') and contains (td[5],'05-04-12')]/td[1]")).getText());
            };


           //go to the new page//

            driver.findElement(By.xpath("html/body/div[3]/div[1]/div/div[3]/div[2]/div[2]/div[3]/div/ul/li/a["+i+"]")).click();
                      for (int second = 0;; second++) {
                if (second >= 60) fail("timeout- nie znalazł 'Wyniki i wygrane Lotto i Lotto Plus' ");
                try { if ("Wyniki i wygrane Lotto i Lotto Plus".equals(driver.findElement(By.cssSelector("h1.title")).getText())) break; } catch (Exception e) {}
                Thread.sleep(50000);
          }

   }

    }
}

All elements are visible on the first page so on first page is ok but when it goes to the second page I get error:

org.openqa.selenium.NoSuchElementException: Unable to locate element: {"method":"xpath","selector":"//div[@id='page']/div[3]/div[2]/div[2]/table/tbody/tr[contains(td[3],'Warszawa') and contains (td[5],'21-02-09')]/td[1]"}
Command duration or timeout: 30.10 seconds
For documentation on this error, please visit: http://seleniumhq.org/exceptions/no_such_element.html

Can anyone help with it. Why I get this error when I use IF statement. 'Webdriver' doesnt find element = doesnt make assertion, does it? So when it doesnt find element then should go further

Please, help me what to do to make it working :)

thanks

Answer 1

The possible cause for this error might be that the element that you are trying to find with xpath :-

//div[@id='page']/div[3]/div[2]/div[2]/table/tbody/tr[contains(td[3],'Warszawa') and contains (td[5],'21-02-09')]/td[1]

is not present in the second page. So, even if you have used if for checking whether the element is present or not, if webdriver could not find the element, then selenium will throw NoSuchElementException exception. To make it simpler, let's put it in this way :-

if (driver.findElement(By.xpath(element_xpath)) != null)
{
  do_some_stuff
}

Now let's break it as follows :-

is_present = driver.findElement(By.xpath(element_xpath))
if(is_present != null)
{
  do_some_stuff
}

The above piece of code is the simplified version of the previous one and this is how your previous code is evaluated while you run the program. That is, first the condition inside if block is evaluated (in your case driver.findElement(By.xpath()) and then the result is compared with null . But in the first case, while webdriver tries to locate the element with the given xpath, it couldn't be found. So at that point itself webdriver throws NoSuchElementException exception. So, once exception is encountered, python doesn't evaluate it any more and the program terminates.

To solve it, put it inside try-catch block :-

 try
   {
    if (driver.findElement(By.xpath(element_xpath)) != null)
      {
       do_some_stuff
      }
   }
 catch(Exception e)
    {
     System.out.println(e);
     System.out.println("Element not found");
    }  

So, even if webdriver finds any Exception failing to locate the given element, instead of terminating the program it will move further and the next piece of your code will be executed, because the catch block will take care of the exception and let your program move further.

I would suggest you to put each if block within try-catch , so, even though any of your if block has an exception , the next if block would not be affected by it's exception .

Hope, this would solve your issue.