"Element is not currently visible and so may not be interacted with" but another is?

Question

I've created another question which I think is the cause for this error: Why does the Selenium Firefox Driver consider my modal not displayed when the parent has overflow:hidden?

Selenium version 2.33.0
Firefox driver

The code that causes the error:

        System.Threading.Thread.Sleep(5000);
        var dimentions = driver.Manage().Window.Size;
        var field = driver.FindElement(By.Id("addEmployees-password")); //displayed is true
        field.Click(); //works fine
        var element = driver.FindElement(By.Id(buttonName)); //displayed is false
        element.Click(); //errors out

The button that its trying to click:

<div id="addEmployees" class="modal hide fade" tabindex="-1" role="dialog" aria-labelledby="addEmployeesLabel" aria-hidden="true">

    <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
        <h3>Add Employee</h3>
    </div>

    <div class="modal-body">
        <p class="alert alert-info">
            <input name="addEmployees-username" id="addEmployees-username" />
            <input name="addEmployees-password" id="addEmployees-password" type="password" />
            <input name="addEmployees-employee" id="addEmployees-employee" />
        </p>
    </div>

    <div class="modal-footer">
        <button name="addEmployees-add" id="addEmployees-add" type="button" class="btn" data-ng-click="submit()">Add</button>
    </div>

</div>

• If I change the call to FindElements then I get ONE element, so there isn't anything else on the page.
• If I FindElement on a field that occurs right before the button, say addEmployees-employee, then addEmployees-employee is displayed
• In the browser itself, it shows up fine, all i need to do is actually click the button and the desired behavior executes, but the webdriver refuses to consider the element displayed

How is it that one field can be considered displayed and the other is not?

The modal with the add button in the bottom right, all the other elements are displayed = true

The window size is 1200x645 per driver.Manage().Window.Size;
The element location is: 800x355y per driver.FindElement(By.Id(buttonName)).Location
The element dimentions are: 51x30 per driver.FindElement(By.Id(buttonName)).Size
The password element location is: 552x233y per driver.FindElement(By.Id("addEmployees-password")).Size

Answer 1

Selenium WebDriver does not just check for opacity != 0, visibility = true, height > 0 and display != none on the current element in question, but it also searches up the DOM's ancestor chain to ensure that there are no parent elements that also match these checkers. (UPDATE After looking at the JSON wire code that all the bindings refer back to, SWD also requires overflow != hidden, as well as a few other cases.)

I would do two things before restructuring the code as @Brian suggests.

1. Ensure that the "div.modal_footer" element does not have any reason for SWD to consider it to not be visible.

2. Inject some Javascript to highlight the element in question in your browser so you know absolutely you have selected the right element. You can use this gist as a starting point. If the button is highlighted in a yellow border, then you know you have the right element selected. If not, it means that the element selected is located elsewhere in the DOM. If this is the case, you probably don't have unique IDs as you would expect, which makes manipulation of the DOM very confusing.

If I had to guess, I would say that number two is what you are running into. This has happened to me as well, where a Dev reused an element ID, causing contention in which element you're supposed to find.