How do I Response.Write from a Sandboxed Solution? - sharepoint

Question

I have a requirement to create an HTML table and shoot it out to the user as a spreadsheet. I've done this many times in plain old ASP.NET, but it's kicking my behind in SharePoint. It's a simple Button with an event handler that calls 3 files stored in a Module (accessible to a sandboxed solution) and then tries to shove the text out to the user along with the appropriate content-type and content-disposition. When I get this part working, the SampleData.txt portion will be replaced with data from multiple lists. Unfortunately, the page does it's postback, but no file is offered to the user for opening or download.
I've read in a few places that Response.Write is not usable in web parts, but surely there is some other way of accomplishing this task...? Here's what I want to do - is there a usable alternative?
protected override void CreateChildControls()
{
Button ReportButton = new Button();
ReportButton.Text = "Generate DCPDS Report";
ReportButton.Click += new EventHandler(ReportButton_Click);
this.Controls.Add(ReportButton);
}
protected void ReportButton_Click(Object sender, EventArgs e)
{
string header = "";
string sampleData = "";
string footer = "";
using (SPWeb webRoot = SPContext.Current.Site.RootWeb)
{
header = webRoot.GetFileAsString("SpreadsheetParts/Header.txt");
sampleData = webRoot.GetFileAsString("SpreadsheetParts/SampleData.txt");
footer = webRoot.GetFileAsString("SpreadsheetParts/Footer.txt");
}
StringBuilder sb = new StringBuilder();
sb.Append(header);
sb.Append(sampleData);
sb.Append(footer);
Page.Response.Clear();
HttpContext.Current.Response.ContentType = "application/vnd.ms-excel";
HttpContext.Current.Response.AddHeader("content-disposition", "attachment; filename=June2010Spreadsheet.xls");
HttpContext.Current.Response.Write(sb.ToString());
//HttpContext.Current.Response.End();
}

Answer 1

I have not tested this, and this would make an interesting Proof of Concept, but I don't have any virgin SharePoint 2010 servers ready for testing, so I cannot test this for you. But just as a thought, could you not place the contents of your excel sheet in a hidden field, and do something like:
HTML:
<script type="text/javascript">
function downloadExcel() {
location.href='data:application/download,' + encodeURIComponent(
document.getElementById('<%= hfExcelData.ClientID %>').value
);
}
</script>
C#:
protected override void CreateChildControls()
{
Button ReportButton = new Button();
ReportButton.Text = "Generate DCPDS Report";
ReportButton.Click += new EventHandler(ReportButton_Click);
this.Controls.Add(ReportButton);
}
protected void ReportButton_Click(Object sender, EventArgs e)
{
string header = "";
string sampleData = "";
string footer = "";
using (SPWeb webRoot = SPContext.Current.Site.RootWeb)
{
header = webRoot.GetFileAsString("SpreadsheetParts/Header.txt");
sampleData = webRoot.GetFileAsString("SpreadsheetParts/SampleData.txt");
footer = webRoot.GetFileAsString("SpreadsheetParts/Footer.txt");
}
StringBuilder sb = new StringBuilder();
sb.Append(header);
sb.Append(sampleData);
sb.Append(footer);
this.hfExcelData.value = sb.ToString();
Page.ClientScript.RegisterStartupScript(this.GetType(), "ExcelUploader", "downloadExcel();", true)
}

Answer 2

I'm struggling with similar. My understanding is that in the sandbox, SP is actually proxying calls to your page, getting the response, and then returning it's own response to the client. That proxy doesn't allow all functions of HttpContext or the SP classes. In my testing, ContentType and headers are not returned. SP (in sandboxed code) will always return text/html and ignore anything else from your webpart.
One way to get the HTML part of what you want is to use an asp:literal. You could follow these steps to create an application page with a webpart on it. Remove the master page reference and the placeholders, so that the only thing returned is your webpart content. In the webpart, add a literal and set the text to the HTML table. At this point, you would have a page that just returns the table as HTML. Here is another post outlining the exact technique. However, you still would not be able to change the content type or add headers. Maybe combined with the first answer that would get you a solution though?

Answer 3

use the default javascript function on a button or linkbutton
STSNavigate(dUrl);
calling the page that creates the HttpContext.Current.Response