Gridview disappears on postback when paging is enabled

Question

I have a gridview that has its DataSourceID property set to a custom ObjectDataSource object. When AllowPaging is set to True, the GridView disappears after a postback. If I set AllowPaging to False it's fine. Can someone shed some light on this for me? :)

Edit: The other thing I'm confused about is I thought that if you set the DataSourceID that the grid would get data from the datasource whenever it needed it. If the grid is disappearing because it's not holding the data, why isn't the gridview getting the data it needs from the datasource?

Answer 1

It's possible that after the postback occurs the datasource is not being maintained or refilled and there are no items to populate the grid. Are you handling state correctly for the datasource object (rebinding/keeping the source alive) when paging is enabled?

This may sound like a vague answer, but without an example of how the source is getting the data it's kind of hard to diagnose why the items would be gone.

Edit:
The method I was thinking of was for callback paging/sorting. However I did find some info ont he ODS & Paging.. make sure you have set the following:

1. GridView: AllowPaging and off course you need to set PageSize.
2. ObjectDataSource: EnablePaging, also you need to set the:
   • MaximumRowsParameterName="maxRows"
   • StartRowIndexParameterName="startRowIndex"
   • SelectCountMethod="RecordCount"

I think you only need to set the 3 sub items of item 2 if you want to handle paging size etc manually.

Then you can read more up on this here.

Answer 2

To answer more of @adam0101's response, what I think he means by "...It turns out my custom datasource was returning zero for the record count.", is that you may need to "re-attach" the datasource to the gridview. ASP.net automatically knows you're retriving record-'n', where 'n' is the next first row of the next page. This solution is more for cases where you don't want to allow asp.net to automatically handle data in your gridview, perhaps due to wanting to load data after another event (a LOAD DATA button for example), and not when the page has loaded for the first time. But as Adam mentioned below the real reason was he "...had created a datasource subclass that inherited ObjectDataSource, but it was implemented incorrectly.". Sorry for my assumption there Adam. Thanks

However, the rest of my solution I think will work for those stuck on using manually derived data sources.

ie

Set your GridView as per above, and note - without a DataSource property! Here is my example:

     <asp:GridView ID="gvStudents" DataKeyNames="StudentID" runat="server" 
            ShowFooter="True" AutoGenerateColumns="False" Width="100%" AllowSorting="True" AllowPaging="true" PageSize="10" OnPageIndexChanging="gvStudents_PageIndexChanging">

Next make a private method or routine that you can call upon when ever you need to force the gridview onto a new page.

private void BindGridViewServer(GridView gv1)
{
    gv1.DataSource = sdsStudents;   //re-attach the datasource
    gv1.DataBind();                 //get a page of data AllowPaging must be true
}

Next, create the OnPageIndexChanging method:

protected void gvStudents_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
    GridView myGV = (GridView)sender;
    myGV.PageIndex = e.NewPageIndex;
    BindGridViewServer(myGV);
}

For the sake of completing this answer, here is my code where I load the data when I want - not when a PostPack is fired, which is the default...

    protected void btnSEARCH(object sender, EventArgs e)
        {
//some code
                    //bind the gridview to the datasource here and then bind!
                    gvStudents.DataSource = sdsStudents;
                    gvStudents.DataBind();
//more code etc
        }