WebBrowser Url to string not work

Question

當代碼到達MessageBox.Show()時，它會拋出一個異常Object reference not set to an instance of an object。

這裏是我的代碼：

WebBrowser webb = new WebBrowser();  
webb.Navigate("https://www.facebook.com/logout.php?next=http://facebook.com&access_token=" + Settings.Default["token"].ToString()); 

MessageBox.Show(webb.Url.AbsoluteUri.ToString()); 

你看到一個原因，這可能是這種情況？

Answer 1

這可能會實現：

WebBrowser webb = new WebBrowser(); 

private void pictureBox3_Click(object sender, EventArgs e) 
{   
    webb.Url = new Uri("https://www.facebook.com/logout.php?next=http://facebook.com&access_token=" + Settings.Default["token"].ToString()); 
    webb.DocumentCompleted += new System.Windows.Forms.WebBrowserDocumentCompletedEventHandler(this.webBrowser1_DocumentCompleted);   
} 

private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e) 
{ 
    MessageBox.Show(webb.Url.AbsoluteUri.ToString()); 
}