question about System.Windows.Forms.WebBrowser

I use a System.Windows.Forms.WebBrowser control in my application:

private System.Windows.Forms.WebB开发者_开发技巧rowser objBrowser;

Anywhere my objBrowser navigated, I want it to have this javascript function:

function alert(message)
{
  window.external.handleMessage(message);
}

that overrides alert function.

When i use this:

private void objBrowser_DocumentCompleted(
    object sender, WebBrowserDocumentCompletedEventArgs e)
{
  objBrowser.Url = new Uri(
    "javascript:function alert(message){window.external.handleMessage(message);};");

  objBrowser.Document.InvokeScript("alert", new object[] { "hello" });//line 1
}

public void handleMessage(object obj)
{
  string msg = obj.ToString();
}

alert function in java script doesn't pass the message into my form. But when i use this:

private void button1_Click(object sender, EventArgs e)
{
  objBrowser.Document.InvokeScript("alert", new object[] { "hello" });
}

private void objBrowser_DocumentCompleted(
    object sender, WebBrowserDocumentCompletedEventArgs e)
{
  objBrowser.Url = new Uri(
    "javascript:function alert(message){window.external.handleMessage(message);};");
}

public void handleMessage(object obj)
{
  string msg = obj.ToString();
}

and click on button1 my form's handleMessage method executed with a object that contains "hello" string.

I want to override alert function in java script in any page that objBrowser will navigate.

How can I do this?

use below code

Private Sub webDest_Navigated(ByVal sender As System.Object, ByVal e As System.Windows.Forms.WebBrowserNavigatedEventArgs) Handles webDest.Navigated
    injectAlertBlocker()

End Sub
Sub injectAlertBlocker()
    Dim head As HtmlElement = webDest.Document.GetElementsByTagName("head")(0)
    Dim scriptEl As HtmlElement = webDest.Document.CreateElement("script")
    Dim element As IHTMLScriptElement = CType(scriptEl.DomElement, IHTMLScriptElement)
    Dim alertBlocker As String = "window.alert = function () { }"
    element.text = alertBlocker
    head.AppendChild(scriptEl)
End Sub