Why I get error when I try to use variable of form class from designer?
Question
In code behind I have property called ReportFeatures and Page_Load event:
public partial class FeatureList : System.Web.UI.Page
{
protected string ReportFeatures;
protected void Page_Load(object sender, EventArgs e)
{
IEnumerable<ReportFeature> featureProps = fim.getFeatureProperties();
ReportFeatures = featureProps.ToJson();
}
}
In designer I tried to access ReportFeatures variable:
<head runat="server">
<title></title>
<script type="text/javascript">
window.reportFeatures = <%= ReportFeatures%>;
</script>
</head>
When page loaded I get this error:
The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).
Any idea why I get that error, and how to fix it?
1 answers
solution1
0 2018-08-20 09:46:56
Instead of using <%= ... %> block, try using data binding expression syntax ( <%# ... %> ), because <%= ... %> implicitly calls Response.Write() method in Page.Header which counts as code block while data binding expression doesn't count:
<head runat="server">
<title></title>
<script type="text/javascript">
window.reportFeatures = <%# ReportFeatures %>;
</script>
</head>
Then add Page.Header.DataBind() method in Page_Load event, because you want to bind ReportFeatures inside <head> tag which contains runat="server" attribute:
protected void Page_Load(object sender, EventArgs e)
{
IEnumerable<ReportFeature> featureProps = fim.getFeatureProperties();
ReportFeatures = featureProps.ToJson();
// add this line
Page.Header.DataBind();
}
More details about this issue can be found here .
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