VB.Net如何设置对对象实例的对象引用? [英] VB.Net How to set an object reference to an instance of an object?

问题描述

使用VB.NET，尝试将页面标题写入文本文件.我被困在这里:

Using VB.NET, trying to write a page title to a text file. I am stumped here:

Private Sub
    Dim pagetitle As String
    pagetitle = WebBrowser1.Document.Title
    My.Computer.FileSystem.WriteAllText("page title.txt", pagetitle, False)

但是我收到一条错误消息:对象引用未设置为对象的实例."请帮忙！

But I get an error saying "Object reference not set to an instance of an object." Please help!

推荐答案

最有可能在Document属性仍然等于Nothing的情况下尝试访问它.将代码移到WebBrowser控件的DocumentCompleted事件中，如下所示:

Most likely you are trying to access the Document property when it is still equal to Nothing. Move your code to the DocumentCompleted event of the WebBrowser control, as such:

Private Sub WebBrowser1_DocumentCompleted(sender As System.Object, e As System.Windows.Forms.WebBrowserDocumentCompletedEventArgs) Handles WebBrowser1.DocumentCompleted
        If WebBrowser1.Document IsNot Nothing Then
            Dim pagetitle As String
            pagetitle = WebBrowser1.Document.Title
            My.Computer.FileSystem.WriteAllText("page title.txt", pagetitle, False)
        End If
End Sub

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