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c# System.NullReferenceException: Object reference not set to an instance of an object

Posted on 2014-02-27
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Last Modified: 2014-02-28
Hello,
Please, help me to find out what is wrong. The code is below.
This is asp code:
<asp:Literal ID="LtError" runat="server" />
<asp:PlaceHolder ID="PhWrapper" runat="server">
<h2>Create New Ballot</h2>
<asp:MultiView ID="MvNewBallot" runat="server" ActiveViewIndex="0">
    <asp:View ID="ViewForm" runat="server">
        <div class="generic-form-section" style="text-align:center";>
                      
              <strong>Candidats:</strong><br />
               <p><strong>1.</strong><asp:TextBox ID="Cand1" Width="313px" runat="server" /><br />
              Information Link:<asp:TextBox ID="TxtLink1" Width="313px" runat="server" /><br /></p>
             <p>2.</strong><asp:TextBox ID="Cand2" Width="313px" runat="server" /><br />
            Information Link:<asp:TextBox ID="TxtLink2"  Width="313px" runat="server" /><br /></p>
       
             <p><strong>Status: </strong><asp:DropDownList ID="DdlStatus" runat="server">
                    <asp:ListItem Text="Active" Value="Active" />
                    <asp:ListItem Text="Inactive" Value="Inactive" Selected="True" />
              </asp:DropDownList></p>
        </div>   
        <p>
            <asp:LinkButton ID="BtnCreate" runat="server" Text="Create Ballot" CssClass="btn" OnClick="BtnCreate_Click" />
        </p>
    </asp:View>
    <asp:View ID="ViewThanks" runat="server">
        <p>The Ballot has been successfully created!</p>
    </asp:View>
</asp:MultiView>
</asp:PlaceHolder>

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And in C#:
protected void BtnCreate_Click(object sender, EventArgs e)
        {
            try
            {
               
               AddNewResponses();
               MvNewBallot.SetActiveView(ViewThanks);
            }
            catch (Exception ex)
            {
                Response.Write(ex);

                LtError.Text = "An error has occurred while attempting to submit your application. <span style=\"display: none;\">" + ex.ToString() + "</span>";
            }
        }
        private void AddNewResponses()
        {
            CDataAccess da = null;
            using (da = new CDataAccess(_connectionString))
            {
                da.OpenConnection();
                int resseq = 0;

                foreach (Control ct in this.Controls)
                {
                    TextBox tb = ct as TextBox;
                    if (tb.ID.Contains("Cand"))
                    {
                        string rlink = "";
                        if (!string.IsNullOrWhiteSpace(tb.Text))   // (tb.Text.Length > 0) //&
                        {
                                ++resseq;
                                da.SelectParameterizedStoredProcedure("AddNewResponse");
                                da.AddInputObject("ResSeq", System.Data.SqlDbType.Int, resseq);
                                da.AddInputObject("ResText", System.Data.SqlDbType.VarChar, tb.Text);
                                if (tb.ID == "Cand1")
                                {
                                    rlink = TxtLink1.Text;
                                }
                                if (tb.ID == "Cand2")
                                {
                                    rlink = TxtLink2.Text;
                                }
                                
                                if (!String.IsNullOrWhiteSpace(rlink))
                                {
                                    da.AddInputObject("ResLink", System.Data.SqlDbType.VarChar, rlink);
                                }
                                da.ExecuteParameterizedCommand();
                                da.ClearResultsAndParameters();
                                da.CloseConnection();
                                da.Dispose();
                            }
                        }
                    }
                }
            }

Open in new window


Everytime i click on Create button i get error:
"System.NullReferenceException: Object reference not set to an instance of an object. at AddNewResponses() "
Any ideas?
Thank you.
0
Comment
Question by:Galina Besselyanova
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4 Comments
 
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 39893875
This line:

TextBox tb = ct as TextBox;

Open in new window


...can result in null if the thing you are attempting to cast is not actually a TextBox. Are you certain that all of the controls you are looping over are actually TextBoxes?
0
 
LVL 13

Accepted Solution

by:
Jitendra Patil earned 2000 total points
ID: 39894326
you need to keep a check for textbox control if you are only concerned about textbox as

you can also do this by the trick given below link using linq.
Finding all controls of a specific type on a page
the above method will save your time and looping part both.

you just need to get all textboxes from the above generic method and do the further processing, by using this you will be sure to get the  controls of type you need.

Hope this helps.
0
 

Author Closing Comment

by:Galina Besselyanova
ID: 39894869
Works like a charm!
Thank you for pointing me in right direction! You saved me a lot of time.
0

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