org.openqa.selenium.WebDriverException: invalid argument: 'handle' must be a string while window handling with Selenium and Java in Linux

I have an requirement of running test cases in CI pipeline. where the VM is linux. Selenium multiple window handling - switchTo() method throws exception for linux platform.

Exception:

org.openqa.selenium.WebDriverException: invalid argument: 'handle' must be a string

Code trials:

driver.switchTo().window(subWindowHandler);

Its declared as per multiple window handle way:

String subWindowHandler = null; 
Set<String> handles = driver.getWindowHandles(); 
Iterator<String> iterator = handles.iterator(); 
while (iterator.hasNext()) { 
    subWindowHandler = iterator.next(); 
}

This code works perfectly in local windows system.

This error message...

org.openqa.selenium.WebDriverException: invalid argument: 'handle' must be a string

...implies that the handle which was passed as an argument needs to be a string.

Logically you are pretty close. Possibly the driver.getWindowHandles() is getting executed too early even before the second window handle is getting created/recognized.

---

Solution

As a solution you need to induce WebDriverWait for numberOfWindowsToBe(2) and you can use the following code block:

String mainWindowHandler = driver.getWindowHandle(); // store mainWindowHandler for future references
//line of code that opens a new TAB / Window
new WebDriverWait(driver, 5).until(ExpectedConditions.numberOfWindowsToBe(2));  //induce WebDriverWait
Set<String> handles = driver.getWindowHandles(); 
Iterator<String> iterator = handles.iterator(); 
while (iterator.hasNext()) 
{ 
    String subWindowHandler = iterator.next(); 
    if (!mainWindowHandler.equalsIgnoreCase(subWindowHandler))
    {
        driver.switchTo().window(subWindowHandler);
    }
}

You can find a relevant detailed discussion in Best way to keep track and iterate through tabs and windows using WindowHandles using Selenium