专家坐堂-[求助]怎样判定是否存在a标签Foxtable(狐表) - 新一代数据库软件，完美融合Access、Foxpro、Excel、vb.net之优势，人人都能掌握的快速软件开发工具!

-- [求助]怎样判定是否存在a标签

各位老师，我想通过以下代码去获取省市县乡村，但这个代码存在漏洞，比如在执行第2级的时候如果是“市辖区”没有a标签，就行提示错误。所以我想求助老师怎么在这个代码中判定有没有a标签

Dim url As String = "http://www.stats.gov.cn/tjsj/tjbz/tjyqhdmhcxhfdm/2015/"

For i As Integer = 11 To 65

Dim web As new System.Windows.Forms.WebBrowser

web.Navigate(url & i & ".html")

Do While web.ReadyState <> 4

Application.DoEvents

Loop

Dim trs = web.Document.GetElementsByTagName("table")(4).GetElementsByTagName("tr")

For j As Integer = 1 To trs.count - 1

Dim tr = trs(j)

Dim tds = tr.GetElementsByTagName("td")

output.show(tds(0).innerText) \'最终显示第2级的ID

output.show(tds(1).innerText) \'最终显示第2级的名称

\' output.show(tds(1).GetElementsByTagName("a")(0).GetAttribute("href"))

Dim web1 As new System.Windows.Forms.WebBrowser

web1.Navigate(tds(1).GetElementsByTagName("a")(0).GetAttribute("href"))

Do While web1.ReadyState <> 4

Application.DoEvents

Loop

Dim trs1 = web1.Document.GetElementsByTagName("table")(4).GetElementsByTagName("tr")

For j1 As Integer = 1 To trs1.count - 1

Dim tr1 = trs1(j1)

Dim tds1 = tr1.GetElementsByTagName("td")

output.show(tds1(0).innerText) \'最终显示第3级的ID

output.show(tds1(1).innerText) \'最终显示第3级的名称

\'output.show(tds1(1).GetElementsByTagName("a")(0).GetAttribute("href"))

Dim web2 As new System.Windows.Forms.WebBrowser

web2.Navigate(tds1(1).GetElementsByTagName("a")(0).GetAttribute("href"))

Do While web2.ReadyState <> 4

Application.DoEvents

Loop

Dim trs2 = web2.Document.GetElementsByTagName("table")(4).GetElementsByTagName("tr")

For j2 As Integer = 1 To trs2.count - 1

Dim tr2 = trs2(j2)

Dim tds2 = tr2.GetElementsByTagName("td")

output.show(tds2(0).innerText) \'最终显示第4级的ID

output.show(tds2(1).innerText) \'最终显示第4级的名称

\'output.show(tds2(1).GetElementsByTagName("a")(0).GetAttribute("href"))

Dim web3 As new System.Windows.Forms.WebBrowser

web3.Navigate(tds2(1).GetElementsByTagName("a")(0).GetAttribute("href"))

Do While web3.ReadyState <> 4

Application.DoEvents

Loop

\' 循环打印di

Dim trs3 = web3.Document.GetElementsByTagName("table")(4).GetElementsByTagName("tr")

For j3 As Integer = 1 To trs3.count - 1

Dim tr3 = trs3(j3)

Dim tds3 = tr3.GetElementsByTagName("td")

output.show(tds3(0).innerText) \'显示第5级Id

\'output.show(tds3(1).innerText) \'显示页面Id

output.show(tds3(2).innerText) \'显示5级名称

\'web3 = Nothing

web3.Dispose

Return ""

\'web2 = Nothing

web2.Dispose

Return ""

\'web1 = Nothing

web1.Dispose

Return ""

web.Dispose

Return ""