元素不再附加到DOM，Selenium WebDriver

Question

情景：

1. 在下拉列表中选择一个值
2. 下载表格
3. 走出循环
4. 选择第二个选项
5. 下载其他表格

但它没有在循环中选择第二个选项并给出此错误消息：

Element is no longer attached to the DOM
Command duration or timeout: 11 milliseconds
For documentation on this error, please visit: http://seleniumhq.org/exceptions/stale_element_reference.html
Build info: version: '2.48.2', revision: '41bccdd', time: '2015-10-09 19:59:12'
System info: host: 'Treselle', ip: '192.168.0.123', os.name: 'Windows 7', os.arch: 'amd64', os.version: '6.1', java.version: '1.7.0_60'
Session ID: 8b83d2b4-acfd-4bb5-9a07-a4155e98dfc1
Driver info: org.openqa.selenium.firefox.FirefoxDriver
Capabilities [{platform=WINDOWS, acceptSslCerts=true, javascriptEnabled=true, cssSelectorsEnabled=true, databaseEnabled=true, browserName=firefox, handlesAlerts=true, nativeEvents=false, webStorageEnabled=true, rotatable=false, locationContextEnabled=true, applicationCacheEnabled=true, takesScreenshot=true, version=45.0}]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

Answer 1

如果DOM在第一次下载中发生了变化，则需要在每次迭代时重新定位下拉列表。您还应该等待报告出现，然后再次查找下拉列表

WebDriverWait wait = new WebDriverWait(driver, 20);
int size = 3;

for (int i = 2 ; i < size ; ++i) {
    WebElement dropdown = driver.findElement(...);
    Select select = new Select(dropdown);
    size = select.getOptions().size(); //change the condition to the number of options
    select.selectByIndex(i);
    driver.findElement(...).click(); //download the report
    wait.until(ExpectedConditions.visibilityOfElementLocated(By.id("ReportViewerControl_AsyncWait_Wait"))); //wait for the loader to appear
    wait.until(ExpectedConditions.invisibilityOfElementLocated(By.id("ReportViewerControl_AsyncWait_Wait"))); //wait for the loader to disappear
}