Exception while in a for-each loop in C# Selenium

Question

IWebElement table = driver.FindElement(By.ClassName("mozaique"));
IList<IWebElement> list = table.FindElements(By.ClassName("thumb-block "));

foreach (var item in list)
{
    item.Click();
    driver.FindElement(By.CssSelector("span.icon.download")).Click();
    waitforDWNlink();
    driver.Navigate().Back();
    driver.Navigate().GoToUrl(URL);
}

The first time when I'm going through the foreach loop it works fine. Inside the foreach loop I navigate to another page. After that, when iterating again in the foreach loop, it gives me an exception.

What am I doing wrong?

EDIT: After seeing one of the answers I tried this:

IWebElement table = driver.FindElement(By.ClassName("mozaique"));
IList<IWebElement> list = table.FindElements(By.ClassName("thumb-block "));

List<string> NewList= new List<string>();
            foreach (var item in list)
            {
                NewList.Add(item.GetAttribute("href"));
            }

I was trying to store the href on a new list item.But after running the code ,the new list item was blank.

Answer 1

You are likely getting a StaleElementException. When you first get the list of elements to click, they are attached to the current DOM. After navigating away (the first time) the elements are no longer attached to the DOM (even if you navigate back). One way of getting around this is to:

1. Get all the HREFs of the elements and store that into a list
2. Visit each HREF and do your actions/verifications

Answer 2

Don't do this:

 foreach (var item in list)

This implies you already have a list of references to existing elements, as soon as you navigate those elements are toast.