Script never seems to register - asp.net

Question

I have the following simple test asp.net form, with following vb.net load event:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim strScript As String
strScript = "function MyMsg()"
strScript += "{"
strScript += "alert(document.getElementById('TextBox3').value);"
strScript += "}"
ClientScript.RegisterStartupScript(Me.GetType(), "MyMsg", strScript, True)
End Sub
It simply displays the contexts of a text box in the web page when the script is called.
I then have this button code:
Protected Sub Button6_Click(sender As Object, e As EventArgs) Handles Button6.Click
If ClientScript.IsStartupScriptRegistered("MyCall") Then
Me.TextBox3.Text = "My text - registered"
Else
Me.TextBox3.Text = "my text NOT registered"
End If
ClientScript.RegisterStartupScript(Me.GetType(), "MyCall", "MyMsg();", True)
End Sub
However, the button when clicked on always shows the text NOT registered. So, the code seems to run ok. It grabs the text from the text box no problme. However, the True part of the code never runs.
Is this a state or scope issue? (or the the fact that the code is only injected one time) that prevents this from running the code block for true?
How can I get the "true" part of the above code to run?

Answer 1

Consolidating(and elaborating on) the comments on the original question here.
The issue is that ASP.NET buttons cause full post backs to the server everytime they are clicked and when a page does a full postback it resets all scripts that may have been registered from previous actions. This means that any script that was registered the last time the button was clicked will be wiped out and the page will not know anything about it the second time around.
There are a few ways to get around this.
UpdatePanel: My prefered way is to declare all your controls that need to be manipulated in the button click handler inside an AJAX Update Panel like:
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
<asp:Button ID="Button1" runat="server" Text="Button" />
</ContentTemplate>
</asp:UpdatePanel>
What this does is limits what the button can change when it is clicked and causes a post back. In order to use this you will also need to declare a Scriptmanager anywhere before the updatepanel. When you register the script you will need to use that scriptmanagers RegisterScriptControl function.
Manual AJAX Postback: Another way to accomplish this would be to use a "manual" AJAX call. I've done this a few times but it is much more complex than the update panel version and I'm not sure if the way that I've done it is the "right" way to go about it. First you will change you ASP button to a regular HTML input button. On the HTML button the onclick should be a javasciprt function that you designate. Inside the javascript function you will need to go through the process of declaring an XMLHttpRequst object. This site goes over how to use the object pretty thoroughly. The way that I have gotten information back and forth is by using the headers attached to the request/response. You need to add them using setRequestHeader function and get them from the getAllResponseHeaders function. Once you get into the page load event on the server side you will need to evaluate the headers of the request and if one exists that signifies that the button was clicked(which you will need to add manually) then you can call a function and add a header to the response that will tell the javascript what to display in the pop up box. I'm sure using headers isn't the best method for getting inormation back and forth but if you are just talking about booleans that only dictate what to print to the user then you probably don't need to go through the process of setting up a JSON or XML response. This is also assuming that you are doing more on the server side than just checking how many times the button has been clicked because if thats all you need to do you should use option 3.
The simplest way to accomplish this would be to make the entire thing a javascript function. Declare a variable(int) on the page and set it to 0 on load. Then when the button is clicked you would just need to check the counter, if its greater than 0 display one message, if its 0 then display a different message. This will only work if your condition is very basic(it can get very complex but sometimes thats overkill).
So, In my opinion, those three options should be able to handle whatever you need to do. The first is very simple to use, the second is very versatile and can become very powerful if you implement XML or JSON in your communications with the server and the third is much faster than communicating with the server every time. Deciding which will be the best fit is up to you.

Answer 2

You did not add the script tag to enclose your script.
Adding function
strScript = "<script type=\"text/javascript\">";
strScript = "function MyMsg()"
strScript += "{"
strScript += "alert(document.getElementById('TextBox3').value);"
strScript += "}"
strScript = "</script>";
ClientScript.RegisterStartupScript(Me.GetType(), "MyMsg", strScript, True)
Calling function
ClientScript.RegisterStartupScript(Me.GetType(), "MyCall", "<script type=\"text/javascript\">MyMsg();</script>", True)