How to Scroll in a Flutter Web App Using Java and Selenium

August 4, 2024

2 minutes

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Flutter has become a popular framework for building web applications due to its fast performance and expressive UI. However, when it comes to automated testing with Selenium, especially for scrolling actions, it can get a bit tricky. In this guide, I’ll show you a quick and reliable way of scrolling within a Flutter web app using Java and Selenium.

We’ll cover how to use the JavaScript Executor to achieve smooth scrolling to specific elements on the page.

Problem: How To Scroll In A Flutter Web App

Scrolling in a Flutter web app isn’t straightforward because the usual Selenium scrolling methods might not work as expected. Flutter manages its own rendering and might not expose the DOM elements in a way traditional web pages do. However, using JavaScript execution, we can overcome this limitation.

Solution: Using JavaScript Executor

JavaScript Executor allows us to run JavaScript code within the context of the browser. This is especially useful for manipulating the page directly, such as scrolling to a particular element.

Locate the Element to Scroll To: Identify the CSS selector for the element you want to scroll into view. In a Flutter web app, this might be wrapped in a flt-semantics tag with an aria-label attribute.
Implement the Scrolling Method: Use the following Java code to scroll to the desired element.

ScrollHelper.class

import org.openqa.selenium.By;
import org.openqa.selenium.JavascriptExecutor;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;

public class ScrollHelper {

  public static void scrollToElement(WebDriver driver) throws InterruptedException {
      // Cast the driver to JavascriptExecutor
      JavascriptExecutor js = (JavascriptExecutor) driver;

      // Find the element using its CSS selector
      WebElement ele = driver.findElement(By.cssSelector("flt-semantics[aria-label={YOUR_SELECTOR}]"));

      // Scroll to the element
      js.executeScript("arguments[0].scrollIntoView({ behavior: 'smooth', block: 'start' });", ele);

      // Wait for the scroll action to complete
      Thread.sleep(2000);
  }
}

Summary

JavascriptExecutor: We cast our WebDriver instance to JavascriptExecutor to execute JavaScript code.
Finding the Element: Use driver.findElement(By.cssSelector(“flt-semantics[aria-label={YOUR_SELECTOR}]”)); to locate the element. Replace {YOUR_SELECTOR} with the actual aria-label of your target element.
Scrolling: The scrollIntoView method ensures the element is brought into the viewport with a smooth scrolling behavior. The block: 'start' option aligns the top of the element with the top of the scrollable area.
Thread.sleep: Adding a delay ensures that the scrolling completes before any further actions are taken. Adjust the sleep duration as needed for your specific use case.

Conclusion

There you go scrolling in a Flutter web app using Selenium can be achieved with the help of JavaScript execution. By targeting the specific elements and using the scrollIntoView method, you can ensure that your automated tests interact with the elements correctly. This approach helps overcome the challenges posed by Flutter’s custom rendering behavior.