Sometimes when you write inline code inside Javascript tag or inside style sheet tag within the header of the page just like code 1, the yellow error page will explode in your face telling you that The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).
Code 1
<%@ Page Language="VB"
AutoEventWireup="false"
CodeFile="Default.aspx.vb" Inherits="_Default"
%>
<!DOCTYPE html PUBLIC
"-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head >
<title>Inline
Code inside JavaScript</title>
<script type="text/javascript" language="javascript">
function
fnTest()
{
var txt
= document.getElementById("<%=
TextBox1.ClientID %>")
alert(txt.value);
}
</script>
</head>
<body>
<form id="form1" runat="server">
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
</form>
</body>
</html>
The weird thing is that the error is not occurred each time! I mean if you tried to write the same code in another page it will work and the error will disappear !!
I searched on the Net to find an answer and to know more about this weird thing, and I found a nice blog that talked about this issue
http://www.west-wind.com/weblog/posts/5758.aspx
He posts a solution for the problem, but the funny thing is that he also did not know the main reason for the error. and I found no one know the main reason!
I tried another solution and it worked for me. All I did is I moved the JavaScript tag to the bottom of the page, typically above the close form tag, and the error is gone!
Solution 1
<%@ Page Language="VB"
AutoEventWireup="false"
CodeFile="Default.aspx.vb" Inherits="_Default"
%>
<!DOCTYPE html PUBLIC
"-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head >
<title>Inline
Code inside JavaScript</title>
</head>
<body>
<form id="form1" runat="server">
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<script type="text/javascript" language="javascript">
function
fnTest()
{
var txt
= document.getElementById("<%=
TextBox1.ClientID %>")
alert(txt.value);
}
</script>
</form>
</body>
</html>
Or you can play around this by registering the JavaScript code from code behind.
Solution 2
Protected Sub Page_Load(ByVal
sender As Object,
ByVal e As
System.EventArgs) Handles Me.Load
Dim
strScript As New
StringBuilder
strScript.Append("function fnTest()")
strScript.Append("{")
strScript.Append("var txt = document.getElementById('")
strScript.Append(Me.TextBox1.ClientID)
strScript.Append("');")
strScript.Append("alert(txt.value);")
strScript.Append("}")
Page.ClientScript.RegisterClientScriptBlock(Me.GetType,
"MyScript", strScript.ToString, True)
End Sub
I really still do not know the error main reason, if anybody know about this then please write it as comment.
I hope someone will found this very helpful.
~ Abdulla AbdelHaq