Here is a VB.Net example if you are trying to retrieve the value of a variable from within a page loaded in a WebBrowser control.
Step 1) Add a COM reference in your project to Microsoft HTML Object Library
Step 2) Next, add this VB.Net code to your Form1 to import the mshtml library:
Imports mshtml
Step 3) Add this VB.Net code above your "Public Class Form1" line:
<System.Runtime.InteropServices.ComVisibleAttribute(True)>
Step 4) Add a WebBrowser control to your project
Step 5) Add this VB.Net code to your Form1_Load function:
WebBrowser1.ObjectForScripting = Me
Step 6) Add this VB.Net sub which will inject a function "CallbackGetVar" into the web page's Javascript:
Public Sub InjectCallbackGetVar(ByRef wb As WebBrowser) Dim head As HtmlElement Dim script As HtmlElement Dim domElement As IHTMLScriptElement head = wb.Document.GetElementsByTagName("head")(0) script = wb.Document.CreateElement("script") domElement = script.DomElement domElement.type = "text/javascript" domElement.text = "function CallbackGetVar(myVar) { window.external.Callback_GetVar(eval(myVar)); }" head.AppendChild(script) End Sub
Step 7) Add the following VB.Net sub which the Javascript will then look for when invoked:
Public Sub Callback_GetVar(ByVal vVar As String) Debug.Print(vVar) End Sub
Step 8) Finally, to invoke the Javascript callback, add this VB.Net code when a button is pressed, or wherever you like:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click WebBrowser1.Document.InvokeScript("CallbackGetVar", New Object() {"NameOfVarToRetrieve"}) End Sub
Step 9) If it surprises you that this works, you may want to read up on the Javascript "eval" function, used in Step 6, which is what makes this possible. It will take a string and determine whether a variable exists with that name, and, if so, returns the valuable invalue of that variable.
