Object reference not set to an instance of an object when records exist

Question

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Hi All,

I know that the above error shows when there are no records found. But in the following case their are 15 records in datatable.

I am trying to show a dropdown list in a column for each row in a gridview. the following is the code in vb:

VB

If dtPersons.Rows.Count > 0 Then
           Dim ddlJuniors As DropDownList = DirectCast(e.Row.FindControl("ddlJuniors"), DropDownList)
           **ddlJuniors.DataSource = dtPersons
           ddlJuniors.DataTextField = "USERN"
           ddlJuniors.DataValueField = "USERID"
           ddlJuniors.DataBind()
       End If

dtPersons table has 15 records as confirmed in debugging.

Following is column in html:

XML

<asp:TemplateField HeaderText="Delegate" HeaderStyle-HorizontalAlign="Left" ControlStyle-Width="100">
                  <ItemTemplate>
                        <asp:DropDownList ID="ddlJuniors" runat="server" DataTextField="USERN" DataValueField="USERID" CssClass="ddl"> </asp:DropDownList>
                </ItemTemplate>
            </asp:TemplateField>

Please suggest.
Thanks
Atul

Posted 15-Oct-14 0:58am

atul sharma 5126

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Sinisa Hajnal · Accepted Answer · 2014-10-15T01:02:00

Solution 1

It doesn't say that datatable is nothing
Your ddlJuniors is probably nothing and accessing ddlJuniors.DataSource fails.

VB

If dtPersons.Rows.Count > 0 Then
If (e.Row.RowType = DataControlRowType.DataRow) Then
           Dim ddlTemp As DropDownList = DirectCast(e.Row.FindControl("ddlJuniors"), DropDownList)
           ddlTemp.DataTextField = "USERN"
           ddlTemp.DataValueField = "USERID"
           ddlTemp.DataSource = dtPersons

           ddlTemp.DataBind()
       End If
End If

Not this code works as follows:
- find in the grid control named ddlJuniors
- assign the found control to local name ddlTemp <-- this can be anything you could call it dasfalksadfj and it would still work
- work with <u>that exact</u> reference through the function

You cannot assign ddlTmp and then try to use ddlJuniors later in the function.

Posted 15-Oct-14 1:02am

Sinisa Hajnal

Updated 17-Oct-14 0:36am

v5

Comments

atul sharma 5126 15-Oct-14 7:19am

You are probably right. After making your suggested changes the error point has changed to:
Dim ddlJuniors As DropDownList = DirectCast(e.Row.FindControl(ddlJuniors.ClientID), DropDownList)

Also highlighed is the ddlJuniors within find control: variable ddljuniors is used before being assigned a value.

Sinisa Hajnal 15-Oct-14 7:59am

You have to rename your local variable so it doesn't clash with found control :)

atul sharma 5126 16-Oct-14 0:53am

the second error resolved. thanks.

But now stuck with the original error of object reference at:
ddlJuniors.DataSource = dtPersons

Sinisa Hajnal 16-Oct-14 6:54am

I think you don't understand the code. You're finding the control ddlJuniors from the web page by findControl("id")

It returns DropDownList object and puts it into the variable you name however you want. It can be just cmb...see solution. You have to change all references in your handler, not just first one.

atul sharma 5126 17-Oct-14 5:59am

I accept your comments with respect. Yes I am new to coding.
But I have used similar code earlier it worked nicely. I have made following changes as per understanding your solution. Pls check and guide. Thanks..

If dtPersons.Rows.Count > 0 Then

dim ddl as dropdownlist = DirectCast(e.Row.FindControl("ddlJuniors"), DropDownList)
**ddl.DataSource = dtPersons
ddl.DataTextField = "USERN"
ddl.DataValueField = "USERID"
ddl.DataBind()
End If

Sinisa Hajnal 17-Oct-14 6:07am

So marked row is the source of the error. I assume ddl is nothing since you use dtPersons in row count checking. I don't know what else to tell you...Try using full name of the control as it appears in HTML after rendering.

In which event are you using the code?

Sinisa Hajnal 17-Oct-14 6:11am

Hmmm...try adding this:
if (e.Row.RowType = DataControlRowType.DataRow)
before trying to find the control (binding will get you headers too)

atul sharma 5126 17-Oct-14 6:29am

BANG ON!!!
DirectCast(e.Row.FindControl("ddlJuniors"), DropDownList) was Nothing as ddlJuniors was in Item template and header row did not have it.

Thanks for the support and patience..

Sinisa Hajnal 17-Oct-14 6:35am

No problem, glad to be of help. I'll just as this to the solution.