Object reference not set to an instance of an object.

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hi , how do i solved this problem?
i want to delete specific row in my gridview and i using btn in the item templates to delete.
here my btn onlick codes and my gridview_rowcommand

C#

protected void Button1_Click(object sender, EventArgs e)
{
    GridViewRow gRow = (GridViewRow)((Button)(sender)).NamingContainer;

    // this line is the one with Object reference not set to an instance of an object error
    string strId =((HiddenField)gRow.FindControl("shoppingCartID")).Value;
}


protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
{
    GridViewRow gRow = (GridViewRow)(((ImageButton)e.CommandSource).NamingContainer);
    int RowIndex = gRow.RowIndex;
}

Posted 17-Jun-13 22:00pm

NooobieCoder

Updated 17-Jun-13 22:46pm

Thanks7872

v2

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_Amy · Answer 1 · 2013-06-17T22:14:00

Solution 1

This error happens when you try to use a property or call a method of an object that is null. You are trying to access an object of GridViewRow gRow, which is null. Try to step through and debug your source code. Try this:

C#

GridViewRow gRow = (GridViewRow)((Button)sender).NamingContainer;

OR

C#

GridViewRow grdRow = (GridViewRow)((Button)sender).Parent.Parent;

--Amit

Posted 17-Jun-13 22:14pm

_Amy

Comments

NooobieCoder 18-Jun-13 5:04am

it is still the same.

NooobieCoder 18-Jun-13 5:06am

i have tried this and get a new problem instead.

protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
{
if (e.CommandName == "Delete")
{
GridViewRow gRow = (GridViewRow)(((Button)e.CommandSource).NamingContainer);
int RowIndex = gRow.RowIndex;
}
}

i get this problem :

ObjectDataSource 'ObjectDataSource' could not find a non-generic method 'Delete' that has parameters

_Amy 18-Jun-13 5:09am

maybe you have bound column instead of button. Can I see your HTML?

NooobieCoder 18-Jun-13 5:11am

i add a button in the item template in gridview which i wan to use. Html of which one?

_Amy 18-Jun-13 5:17am

Then check for shoppingCartID, whether it exists in itemtemplate or not.

NooobieCoder 18-Jun-13 5:21am

sry but how do i check for the shoppingCartID?

_Amy 18-Jun-13 5:24am

It a HiddenField in your itemtemplate, right? If yes, then only you can able to find shoppingCartID.

NooobieCoder 18-Jun-13 5:29am

but my itemtemplate only have button no hiddenfield.

_Amy 18-Jun-13 5:31am

Then why you are finding hidden field? Why you've written this code:

// this line is the one with Object reference not set to an instance of an object error
string strId =((HiddenField)gRow.FindControl("shoppingCartID")).Value;

--Amit

NooobieCoder 18-Jun-13 5:38am

i got this code from online:x

_Amy 18-Jun-13 5:51am

Then add the hiddenfield in your itemtemplate.

NooobieCoder 18-Jun-13 5:43am

so i should change to what code?

_Amy 18-Jun-13 5:50am

Then add a HiddenField in that ItemTemplate named shoppingCartID, then try.

NooobieCoder 18-Jun-13 6:03am

hmm it not working

_Amy 18-Jun-13 6:10am

You need to start from beginning. Copying code from internet is not the solution for all kind of problem. You need to learn from basics.
Read GridView Examples for ASP.NET 2.0: Working with TemplateFields[^].
--Amit

Zafar Sultan · Answer 2 · 2013-06-17T23:30:00

Solution 2

Since you want to perform CRUD operations using objectdatasource, this[^] is a very nice article to get started.

Posted 17-Jun-13 23:30pm

Zafar Sultan

Updated 18-Jun-13 4:36am

v2

Comments

NooobieCoder 18-Jun-13 5:41am

how to write the deletion method?sry I am very bad CRUD especially with gridview

Zafar Sultan 18-Jun-13 5:45am

It's all right. Once you get till here(obtaining the id of record to be deleted) it's not that difficult. All you have to do is to call SP that deletes the record based on its ID passed as parameter.

NooobieCoder 18-Jun-13 5:42am

bad at*

Zafar Sultan 18-Jun-13 5:48am

You can find a very good article about CRUD operations at http://www.dotnetfunda.com/articles/article1619-how-to-perform-edit-update-and-delete-operation-in-gridview.aspx

NooobieCoder 18-Jun-13 5:48am

SP?

Zafar Sultan 18-Jun-13 5:54am

Stored Procedure.

NooobieCoder 18-Jun-13 5:54am

isit something like that?
int ShoppingCartID = GridView1.DataKeys[e.RowIndex].Value;
using (SqlConnection conn = new SqlConnection())
{
string sql = "Delete from PersonalDetail" +
" where shoppingCartID = @shoppingCartID";
using (SqlCommand cmd = new SqlCommand(sql, conn))
{
cmd.Parameters.AddWithValue(
"@shoppingCartID", ShoppingCartID);
conn.Open();
cmd.ExecuteNonQuery();
conn.Close();
}
}

Zafar Sultan 18-Jun-13 5:59am

Nearly. You are using parameterized query and I am talking about stored procedure. Your code is good enough. Just write it inside GridView1_RowCommand event after what I have suggested. It will work.

NooobieCoder 18-Jun-13 6:15am

but there an error with RowIndex

NooobieCoder 18-Jun-13 6:24am

system.web.ui.webcontrols.gridviewCommandeventargs does not contain a definition for rowindex and no extension method rowindex accepting a first argument of type system.web.ui.webcontrols.gridviewcommandeventargs could be found.

Zafar Sultan 18-Jun-13 6:45am

You will have to replace
int ShoppingCartID = GridView1.DataKeys[e.RowIndex].Value;
with
int ShoppingCartID = Convert.ToInt32(e.CommandArgument);

NooobieCoder 18-Jun-13 6:58am

when i put that it show me : input string was not in correct format.

Zafar Sultan 18-Jun-13 7:04am

Update your question and post your Gridview's HTML and RowCommandEvent code.

NooobieCoder 18-Jun-13 7:21am

protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
{
string strId = e.CommandArgument.ToString();
//int ShoppingCartID = GridView1.DataKeys[e.RowIndex].Value;
int ShoppingCartID = Convert.ToInt32(e.CommandArgument);
using (SqlConnection conn = new SqlConnection())
{
string sql = "Delete from BQ_ShoppingCart" +
" where shoppingCartID = @shoppingCartID";
using (SqlCommand cmd = new SqlCommand(sql, conn))
{
cmd.Parameters.AddWithValue(
"@shoppingCartID", ShoppingCartID);
conn.Open();
cmd.ExecuteNonQuery();
conn.Close();
}
}
}

NooobieCoder 18-Jun-13 7:21am

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataSourceID="ObjectDataSource1"
style="margin-right: 0px" onrowdatabound="GridView1_RowDataBound"
AllowPaging="True" DataKeyNames="shoppingCartID"
onrowcommand="GridView1_RowCommand">
<columns>
<asp:TemplateField>
<itemtemplate>
<asp:Button ID="Button1" runat="server" Text="delete"
CommandArgument="shoppingCartID" CommandName="DeleteRecord" />

<asp:BoundField DataField="productID" HeaderText="ID" />
<asp:BoundField DataField="productName" HeaderText="Name" />
<asp:BoundField DataField="quantity" HeaderText="Qty" />
<asp:BoundField DataField="productPrice" DataFormatString="{0:c}"
HeaderText="Price" />
<asp:BoundField DataField="productDescription" HeaderText="Desc" />
<asp:BoundField HeaderText="Sub Total" />

Zafar Sultan 18-Jun-13 8:31am

Well, you are using DataSource object to bind gridview. In this case performing CRUD operations can also be done using example at http://highoncoding.com/Articles/139_GridView_With_ObjectDataSource.aspx

Anyways, the error you are getting is because of wrong evaluation of command argument. You must supply it as CommandArgument = '<%# Eval("shoppingCartID") %>'

Try this and reply.

NooobieCoder 18-Jun-13 9:42am

after changing it, now my error is

ObjectDataSource 'ObjectDataSource1' could not find a non-generic method 'DeleteItem' that has parameters: ShoppingCartID, original_shoppingCartID

Zafar Sultan 18-Jun-13 10:35am

As I stated you are using ObjectDataSource to bind the data. So updation, deletion and adding must be performed on the same source. Do one thing, use the link I provided in my previous comment(http://highoncoding.com/Articles/139_GridView_With_ObjectDataSource.aspx) to achieve the same. I am also updating my Reply.

NooobieCoder 18-Jun-13 11:19am

from the link u gave,

SqlConnection myConnection = new SqlConnection(ConnectionString);

SqlCommand myCommand = new SqlCommand(SP_DELETE_USER, myConnection);

myCommand.Parameters.AddWithValue("@UserID", id);

myConnection.Open();

myCommand.ExecuteNonQuery();

myConnection.Close();

the sp_delete_user what shd i changed to?

Zafar Sultan 18-Jun-13 11:25am

Replace these two lines:
SqlCommand myCommand = new SqlCommand(SP_DELETE_USER, myConnection); myCommand.Parameters.AddWithValue("@UserID", id);
with:
string sql = "Delete from BQ_ShoppingCart" + " where shoppingCartID = @shoppingCartID"; SqlCommand cmd = new SqlCommand(sql, conn);
cmd.Parameters.AddWithValue("@shoppingCartID", ShoppingCartID);
cmd.CommandType = CommandType.Text;

Keep everything else intact.

NooobieCoder 18-Jun-13 11:44am

SqlConnection myConnection = new SqlConnection("DKGWConnectionString");

string sql = "Delete from BQ_ShoppingCart" + " where shoppingCartID = @shoppingCartID"; SqlCommand cmd = new SqlCommand(sql, conn);
cmd.Parameters.AddWithValue("@shoppingCartID", ShoppingCartID);
cmd.CommandType = CommandType.Text;

myConnection.Open();

myCommand.ExecuteNonQuery();

myConnection.Close();

isit like that?
i have error on myCommand and conn

Zafar Sultan 18-Jun-13 11:59am

It's like:

SqlConnection myConnection = new SqlConnection("DKGWConnectionString");//"DKGWConnectionString" has to be a connection string. Not a string.
myConnection.Open();
string sql = "Delete from BQ_ShoppingCart" + " where shoppingCartID = @shoppingCartID"; SqlCommand cmd = new SqlCommand(sql, myConnection); cmd.Parameters.AddWithValue("@shoppingCartID", ShoppingCartID);
cmd.CommandType = CommandType.Text;
cmd.ExecuteNonQuery();
myConnection.Close();

NooobieCoder 18-Jun-13 12:39pm

now they say BQ_DAL.deleteitem(int) : not all code paths return a value?
is it because i allow null in my db table?

NooobieCoder 19-Jun-13 0:13am

SqlCommand(sql, myConnection);
i change it to sqlCommand(sql.ToInt32, myConnection)
however same problem occur again
ObjectDataSource 'ObjectDataSource1' could not find a non-generic method 'DeleteItem' that has parameters: ShoppingCartID, original_shoppingCartID.