Null Reference Exception when attempting to bind dropdownlist inside formview

Question

I have an edit button and a dropdownlist inside a formview. I am using Linq To Entities to get the data I need to work with and have no problem populating and viewing the formview itemtemplate.

However, the dropdownlist control (id="ddlEligibility") is only in theedititemtemplate (I use a textbox in the itemtemplate to display the current value) and I am having a problem binding this control to the datasource.

Specifically, when I click the Edit button I am getting a NullReferenceException - "Object not set to an instance of an object" on the last line of code below. Does anyone have an idea what I am doing wrong?

protected void btnEdit_Click(object sender, EventArgs e)
{
    fvSubscriber.ChangeMode(FormViewMode.Edit);
    fvSubscriber.DataBind(); // Adding this line solved the first problem where I could not find the control

    LifeLineDSEntities context = new LifeLineDSEntities():

    var program = from p in context.EligibilityPrograms
                  select p;

    DropDownList ddlEligibility = (DropDownList)(fvSubscriber.FindControl("ddlEligibility")));

    if (ddlEligibility != null)
    {
        ddlEligibility.DataSource = program;
        ddlEligibility.DataTextField = "ProgramName";
        ddlEligibility.DataValueField = "eligibilityCode";
        ddlEligibility.DataBind();
        statusMessage.InnerHtml = "It is NOT null";
    }
    else
    {
        statusMessage.InnerHtml = "It is null";
    }
}

DropDownlist in FormView...

<form id="form1" runat="server">
    <asp:FormView ID="fvSubscriber" runat="server" RenderOuterTable="false" DefaultMode="Readonly" OnModeChanging="fvSubscriberChanging">
        <ItemTemplate>
           // mark up here
        </ItemTemplate>
        <EditItemTemplate>
            <asp:DropDownList ID="ddlEligibility" runat="server" />
        </EditItemTemplate>
    </asp:FormView>
</form>

UPDATE: I tried the FindControlRecursive method discussed in the accepted answer in the link below (for FormView though) to see if for some reason the control was not where I thought it was but still no luck, it always comes back null. When I view source on the page, the control "ddlEligibility" is there.

ASP.net .FindControl() and GridView returning null

New Update I was able to find the control by adding fvSubsriber.databind() as shown in the code above, however I am unable to get the edititemtemplate to show the value in the dropdownlist that was displayed in the itemtemplate. In the edititemtemplate is just default to the first item in dropdownlist. I have added the code above. I have moved this new problem to a new post

Most likely, it cannot find the control ddlEligibility. Are you sure it exists? — Dude0001, Nov 12 '13 at 20:00
Have you tried putting ddlEligibility into a variable of type DropDownList to make sure it can be found? That'd be my most likely guess as to the problem — Andrew, Nov 12 '13 at 20:00
@Christopher Stevenson fvSubscriber isn't null, or he would have got an error on the third line calling fvSubscriber.ChangeMode — Dude0001, Nov 12 '13 at 20:02

meda · Accepted Answer · 2013-11-12T20:20:06.487

0

You can try like this, peform a check before giving a datasource

var ddlEligibility = ((DropDownList)(fvSubscriber.FindControl("ddlEligibility")));

if(ddlEligibility!=null)
{
   ddlEligibility.DataSource = program;
   ddlEligibility.DataBind();
} 
else
{
   statusMesage.InnerHtml = "IT IS NULL";
}

edited Nov 12 '13 at 20:20

answered Nov 12 '13 at 20:02

meda

45,103
14
92
122

2

Actually that kind of cast throws an exception. You would need `var ddlEligibility = (fvSubscriber.FindControl("ddlEligibility")) as DropDownList;` to get a null value. – Christopher Stevenson Nov 12 '13 at 20:04
Hello meda, Thanks for your help. I am not getting the null exception now, however my dropdownlist is empty. – Jason Nov 12 '13 at 20:10
@Jason you have to bind the dropdown to the datasource after assinging it, see my update – meda Nov 12 '13 at 20:13
1

@ChristopherStevenson the exception is thrown when you attempt to access the control but is null this is why I added the condition – meda Nov 12 '13 at 20:16
@meda If this object you're casting is not in fact a DropDownList, you would get a CastException. As an implementer, you need to decide if that exception is an error to fix, or an error to ignore. – Christopher Stevenson Nov 12 '13 at 20:19
@meda, I added the else statement to my code and am getting the message so apparently ddlEligibility is null. – Jason Nov 12 '13 at 20:19
@Jason how did you create `ddlEligibility` show it in your post – meda Nov 12 '13 at 20:21
@meda I added the markup to my post that creates ddlEligibility – Jason Nov 12 '13 at 22:10

Null Reference Exception when attempting to bind dropdownlist inside formview

1 Answers1