在Visual Studio窗体的WebBrowser控件中,此代码可以正常工作:
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
WebBrowser1.DocumentText =
"<html><body>Search in Google:<br/>" &
"<form method='get' action='http://www.google.com/search'>" &
"<input type='text' name='as_q'/><br/>" &
"<input type='submit' value='Search'/>" &
"</form></body></html>"
End Sub
当我将以下代码添加到通过WebBrowser Document属性验证HTML表单时,请收到以下错误消息:对象引用未设置为对象的实例。
Private Sub WebBrowser1_Navigating(sender As Object, e As WebBrowserNavigatingEventArgs) Handles WebBrowser1.Navigating
Dim document = WebBrowser1.Document
If document IsNot Nothing And
document.All("as_q") IsNot Nothing And
String.IsNullOrEmpty(
document.All("as_q").GetAttribute("value")) Then
e.Cancel = True
MsgBox("Please enter a search term.")
End If
End Sub
答案 0 :(得分:1)
将您的所有And
更改为AndAlso
...截至目前,您仍在尝试评估逻辑。
当您使用AndAlso
时,它会短路并在不符合条件时跳出。