What is the problem? JavaScript - ListBox

[Steven M]

Hello!!!

I dont know what is the problem!!! I am desperate!!! I want to put
enabled = false a button when in ListBox has selected more than a
item.

this is the javascript.
it dosen't Work!!!!

<script language =javascript>
function JavaListBox()
{
var Contador = 0;
for (var i=0;i< document.all('ListBox1').options.length;i++)
{
if (document.all('ListBox1').options.selected == true)
{
Contador++;
}
}
if (Contador > 1)
{
document.all('btnMio').disabled = true;
}
else
{
document.all('btnMio').disabled = false;
}
}
</script>


here is the real code (codebehind)


private void Page_Load(object sender, System.EventArgs e)
{
this.RegisterStartupScript("JListBox",JavaScriptListBox());
}

private void ListBox1_PreRender(object sender, System.EventArgs e)
{
ListBox1.Attributes.Add("OnClick", "JavaListBox()");
}


private string JavaScriptListBox()
{
StringBuilder strMetodo = new StringBuilder();
strMetodo.Append("<script language=\"javascript\">");
strMetodo.Append("function JavaListBox(){");
strMetodo.Append("var Contador = 0;");
strMetodo.Append("for (var i=0;i<
document.all('ListBox1').options.length;i++)");
strMetodo.Append("{");
strMetodo.Append("alert('Entro For');");
strMetodo.Append("if (document.all('ListBox1').options.selected ==
true)");
strMetodo.Append("{");
strMetodo.Append("Contador++;");
strMetodo.Append("}");
strMetodo.Append("}");
strMetodo.Append("if (Contador > 1){ document.all('btnMio').disabled =
true}");
strMetodo.Append("else {document.all('btnMio').disabled = false}");
strMetodo.Append("}");
strMetodo.Append("</script>");
return strMetodo.ToString();
}

 

[Karl Seguin]

You probably want to use the onChange event instead of onClick. It'll work
with OnClick but oddly (only when the select is clicked). That's assuming
you have all the right id's

Karl