r - 如何使用 RSelenium 检查网页中是否存在元素？

Question

我一直试图从一个网站获取特性列表数据，该网站有时有一个“查看更多”按钮来加载更多结果，但有时却没有。在第一种情况下，我一直在使用下面的代码，它工作正常。例如，

  url<- "http://www.magicbricks.com/property-for-rent/residential-real-estate?bedroom=2&proptype=Multistorey-Apartment,Builder-Floor-Apartment,Penthouse,Studio-Apartment,Service-Apartment,Residential-House,Villa&cityName=Navi-Mumbai&Locality=Vashi"
  remDr$navigate(url)
  Sys.sleep(3)
  webElem <- remDr$findElement("css", "#viewMoreButton a")
  while(webElem$isElementDisplayed()[[1]]){
    tryCatch({
      Sys.sleep(1)
      webElem <- remDr$findElement("css", "#viewMoreButton a")
      webElem$clickElement()
    }, error=function(e){})
  }
  mb<- read_html(remDr$getPageSource()[[1]])

但在第二种情况下，它不起作用。例如:

  url<- "http://www.magicbricks.com/property-for-rent/residential-real-estate?bedroom=4&proptype=Multistorey-Apartment,Builder-Floor-Apartment,Penthouse,Studio-Apartment,Service-Apartment,Residential-House,Villa&cityName=Navi-Mumbai&Locality=Vashi"
  remDr$navigate(url)
  Sys.sleep(3)
  webElem <- remDr$findElement("css", "#viewMoreButton a")
  while(webElem$isElementDisplayed()[[1]]){
    tryCatch({
      Sys.sleep(1)
      webElem <- remDr$findElement("css", "#viewMoreButton a")
      webElem$clickElement()
    }, error=function(e){})
  }
  mb<- read_html(remDr$getPageSource()[[1]])

此代码卡在“WebElem<- renDr$findElement()”行，不会向前移动或抛出错误。

我做错了什么？

Answer 1

添加 if 条件解决问题:

  url<- "http://www.magicbricks.com/property-for-rent/residential-real-estate?bedroom=4&proptype=Multistorey-Apartment,Builder-Floor-Apartment,Penthouse,Studio-Apartment,Service-Apartment,Residential-House,Villa&cityName=Navi-Mumbai&Locality=Vashi"
  remDr$navigate(url)
  Sys.sleep(3)
  if(length(remDr$findElements("css", "#viewMoreButton a"))!=0){
    while(webElem$isElementDisplayed()[[1]]){
      tryCatch({
      Sys.sleep(1)
      webElem <- remDr$findElement("css", "#viewMoreButton a")
      webElem$clickElement()
      }, error=function(e){})
    }
  }
  mb<- read_html(remDr$getPageSource()[[1]])