CODEWITHSUNDEEP
c#asp.net.net
Hoff
Hoff

Reputation: 1772

FormView.DataItem is null on postback

I am using a LinqDataSource and a FormView with paging enabled on an ASP.NET page. I am trying to access the FormView's DataItem property on PageLoad and I have no trouble on the first page load, but as soon as I use the Next/Prev page button (causing a postback) on the FormView the DataItem property is null, even if there a record showing in the FormView. Any ideas why it works fine on the first page load but not on a postback?

If you're curious what my PageLoad event looks like, here it is:

protected void Page_Load(object sender, EventArgs e)
{
    Label lbl = (Label)fvData.FindControl("AREALabel");
    if (fvData.DataItem != null && lbl != null)
    {
        INSTRUMENT_LOOP_DESCRIPTION record = (INSTRUMENT_LOOP_DESCRIPTION)fvData.DataItem;
        var area = db.AREAs.SingleOrDefault(q => q.AREA1 == record.AREA);
        if (area != null)
            lbl.Text = area.AREA_NAME;
    }
}

Upvotes: 4

Views: 4639

Answers (2)

Jupaol
Jupaol

Reputation: 21365

The object you bind to any data-bound control won't be persisted in the page's ViewState

Therefore, on subsequent posts the DataItem property will be null unless you re-bind the control

This property will contain a reference to the object when the control is bound.

Usually you would need to access this property if you want to do something when the objects is bound, so you need to react to the DataBound event

Example:

Output

enter image description here

Code behind

protected void ds_DataBound(object sender, EventArgs e)
{
    var d = this.fv.DataItem as employee;
    this.lbl.Text = d.lname;
}

ASPX

    <asp:LinqDataSource ID="lds" runat="server"
        ContextTypeName="DataClassesDataContext"
        TableName="employees" 
    >

    </asp:LinqDataSource>
    <asp:FormView runat="server" ID="fv" DataSourceID="lds" AllowPaging="true" 
        OnDataBound="ds_DataBound">
        <ItemTemplate>
            <asp:TextBox Text='<%# Bind("fname") %>' runat="server" ID="txt" />
        </ItemTemplate>
    </asp:FormView>
    <br />
    <asp:Label ID="lbl" runat="server" />

Upvotes: 5

gws2
gws2

Reputation: 609

Your data will not be preserved on PostBack. You'll need to rebind the FormView in the PageIndexChanging event using something like: 

protected void FormView_PageIndexChanging(object sender, FormViewPageEventArgs e)
{
    FormView.PageIndex = e.NewPageIndex;
    //rebind your data here
}

Upvotes: 0

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