Persisting DataSource in GridView after PostBack

Question

So I have a GridView in my ASPX page.

When I click <asp:Button id="btnBindIt" runat="server" /> it binds a datatable as follows:

theDataTable = GetAllTheRecords();
gvTheGridView.DataSource = theDataTable;
gvTheGridView.DataBind();

Note: theDataTable is a member

private DataTable theDataTable;

This works as expected.

Now, after the GridView is displayed nicely, I want to export the data to CSV, so I now click the <asp:Button id="btnExportIt" runat="server" /> which runs the code:

exportToCsv(theDataTable);

but theDataTable is null.

So I tried

exportToCsv(gvTheGridView.DataSource)

Which is also null.

What's the standard way of persisting this data? I don't really want to hit the DB again as it's quite a long SPROC and the user has already waited once.

Thanks in advance!

Susy

Answer 1

Thanks for the answers everyone.

I steer clear of putting stuff into the VeiwState or session unnecessarily, so I think the best way to persist this data is to Cache it.

I think the MemoryCache is the most appropriate place for this, is is how I ended up implementing it.

Susy

-1: #15408617 – Syriac

I think it's a bad idea to store large amounts of data like this in the session. For me, my solution was to not store the results that I planned on databinding, but to make the query that got the results faster by caching. It worked well for my situation. – Susy

Answer 2

Class level variables can't maintain their value on postback.

But there are two ways you can maintain Data on the Page's PostBack: ViewState and Session State. But I would suggest in your Scenario to put it in the ViewState.

ViewState["theDataTable"] = theDataTable;
Session["theDataTable"] = theDataTable;

And then you can access it on the page postback:

DataTable theDataTable = (DataTable)ViewState["theDataTable"];
DataTable theDataTable = (DataTable)Session["theDataTable"];

Maladjustment

Thank Muhammed. I'm concerned with using the session or viewstate with a large dataset. Would you recommend doing this for a large dataset? – Susy

What if you export Gridview data to CSV ? – Maladjustment

Another way is, you can iterate your Gridview Rows on server and extract DataTable from Gridview and then export it csv. – Maladjustment

Answer 3

Declare the datatable as follows and everything will work as expected

    private string _theDataTable="theDataTable";
    private DataTable theDataTable
    {
            get
            {
                    if(ViewState[_theDataTable]==null)
                            return new DataTable();
                    return (DataTable)ViewState[_theDataTable];
            }
            set
            {
                    ViewState[_theDataTable] = value;
            }
    }

cheers!

Crept

instead of writing return new DataTable(); in case of ViewState being null, it would be better to get fresh data from the data source (database or what ever it is). – Cattery