Unable to switch to iframe using Selenium Webdriver - selenium

Question

I am trying to learn the feature drag and drop in the webpage
Link
The Section Books is inside the iframe.
But i am unable to access the iframe I am getting below error
no such element: Unable to locate element:
Below are the Xpath i tried
// WebElement frame =driver.findElement(By.xpath("//div[#id='root']//iframe[#class='st-preview-body']"));
// WebElement frame =driver.findElement(By.tagName("iframe"));
WebElement frame =driver.findElement(By.xpath("//iframe[#src='https://snippet.webixcode.com/snippet.html?0.0.3']"));
driver.switchTo().frame(frame);
I also tried using by.id and also xpath using id and class name
What will be the mistake i am doing? To my knowledge there is only one iframe present
The code for drag and drop. will this work?
WebElement fromdrag=driver.findElement(By.xpath("//span[#class='dhx_tree-list-item__text'][normalize-space()='Lawrence Block']"));
WebElement todrop=driver.findElement(By.id("treeTarget"));
Actions act=new Actions(driver);
act.dragAndDrop(fromdrag, todrop).build().perform();

Answer 1

Its a Nested iframe. We need to switch to those iframes one by one to access Elements from All Books.
The page takes time to load, better apply Explicit waits to find the Elements. And you also need to driver.switchTo().defaultContent(); to come out of the iframe and find Elements outside the iframe
public void iframequestion() {
System.setProperty("webdriver.chrome.driver","C:\\expediaproject\\Chromedriver\\chromedriver.exe");
driver = new ChromeDriver();
driver.manage().window().maximize();
driver.manage().timeouts().implicitlyWait(30, TimeUnit.SECONDS);
JavascriptExecutor js = (JavascriptExecutor)driver;
driver.get("https://dhtmlx.com/docs/products/dhtmlxTree/");
WebElement frame1 = driver.findElement(By.xpath("//iframe[#src='https://snippet.dhtmlx.com/3e0b5r57?mode=mobile']"));
js.executeScript("arguments[0].scrollIntoView(true);", frame1);
driver.switchTo().frame(frame1);
WebElement frame2 = driver.findElement(By.xpath("//iframe[#class='st-preview-body']"));
driver.switchTo().frame(frame2);
WebElement frame3 = driver.findElement(By.id("content"));
driver.switchTo().frame(frame3);
WebElement ele1 = driver.findElement(By.xpath("//span[text()='Fiction & Fantasy']"));
System.out.println(ele1.getText());
driver.switchTo().defaultContent();
WebElement ele2 = driver.findElement(By.xpath("//a[text()='View more demos']"));
System.out.println(ele2.getText());
driver.quit();
}
Fiction & Fantasy
View more demos