添加的vline不会出现在情节中

Question

我有这个情节

 dat = data.frame(x = c(55,56) , y = c(200,300))
    ggplot(dat, aes(x = factor(x, ordered = TRUE), y =y)) +
      geom_bar(stat = "identity")+
      geom_vline(aes(xintercept =  55, linetype = "solid"   ), color = "red")

垂直线未出现。如何让它出现在酒吧上方？谢谢。