在 VB.net 中的 WebBrowser 控件中需要帮助

问题描述：

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        WebBrowser.Show()
        WebBrowser.WebBrowser1.Navigate("www.carsonmap.com/hidalgo/login.cfm")
        WebBrowser.WebBrowser1.Document.GetElementById("UserName").SetAttribute("value", "lrgvdc")
        WebBrowser.WebBrowser1.Document.GetElementById("PW").SetAttribute("value", WebBrowser.TextBox2.Text)
    End Sub

我需要有关此代码的帮助，我一直收到一条错误消息，指出空引用.

I need help with this code I keep getting an error saying Null Reference.

我从这个 Youtube 视频中得到了这个想法，看看我想要完成什么.

I got the idea from this Youtube Video check out to see what I am trying to accomplish.

https://www.youtube.com/watch?v=9EJXzWasTq4&list=PL42055376AE25291E&index=41他们使用两个按钮进入我正在尝试进入的网站通过使用一个按钮了解为什么它不起作用.

https://www.youtube.com/watch?v=9EJXzWasTq4&list=PL42055376AE25291E&index=41 They used two buttons to enter to the website I am trying to enter to a website By using one button any ideas why doesnt it work.

答

当您使用 WebBrowser1.Navigate - 刚开始加载文档时，该文档无法立即使用.

When you use WebBrowser1.Navigate - it just begins to load document, the document is not available right away.

您需要使用 WebBrowser.DocumentCompleted 事件将您的代码放置在文档元素上.例如.类似的东西

You need to use WebBrowser.DocumentCompleted Event to place your code that works on document's elements. E.g. something like

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
  WebBrowser.Show()
  WebBrowser.WebBrowser1.Navigate("www.carsonmap.com/hidalgo/login.cfm")
End Sub



Private Sub WebBrowser1_DocumentCompleted(ByVal sender As Object, _
    ByVal e As WebBrowserDocumentCompletedEventArgs) Handles WebBrowser1.DocumentCompleted

  WebBrowser.WebBrowser1.Document.GetElementById("UserName").SetAttribute("value", "lrgvdc")
  WebBrowser.WebBrowser1.Document.GetElementById("PW").SetAttribute("value",    WebBrowser.TextBox2.Text)

End Sub

在 VB.net 中的 WebBrowser 控件中需要帮助

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