Thanks for help me my problem is solved , error is generating because i m not giving the column name
i was using MessageBox.Show(dataGridView1.Rows[1].Cells[1].Value.ToString());
but need
MessageBox.Show(dataGridView1.Rows[1].Cells["Name"].Value.ToString());

A null check will solve this problem.
Paste your code here. Then I can tell you the exact reason for this and give you the solution.

actually i have fill the name , class.. cloumns of datagridview with some database table and it displayed properly,
But when i want to show these cells values in messagebox it shows same null values error , why?
MessageBox.Show(dataGridView1.Rows[1].Cells[1].Value.ToString());

But it gives error: Object reference not set to an instance of an object.
why?

Hi Vikas and Kritan,
 
If you use 'Value' property, you will notice that, sometimes it returns false eventhough the checkbox is checked. Because this 'Value' contains only the 'committed' value.  This is not similar to our expected value always.
Kritan, you can refer to this if you like.
http://msdn.microsoft.com/en-us/library/system.windows.forms.datagridviewcell.editedformattedvalue.aspx
 
 
So Vikas, Do not use 'value' property. Instead use 'DataGridViewCell.EditedFormattedValue' as I have given in my code.
 

foreach(DataGridViewRow r in dataGridView1.Rows)    {                       DataGridViewCheckBoxCell chk3 = (DataGridViewCheckBoxCell)r.Cells[3];       if (Convert.ToInt32(chk3.EditedFormattedValue) == 1)       {                          //Check box is checked.         // Write your code here.       }       else       {          //Checkbox is not checked.       } }

 
If my answer helps you please accept my answer.
 
Thanks

Hi Vikas,
 
To check whether the check box is checked or not you can use my code.
Here, I have written the code to check cell 3. You can use the same code for all the other check boxes.
 

DataGridViewCheckBoxCell chk3 = (DataGridViewCheckBoxCell)r.Cells[3]; if (Convert.ToInt32(chk3.EditedFormattedValue) == 1) {        //This checks whether the check box is checked.       // Write your code here. }

 
If this answer helps you please accept my answer. :)
 
Thanks

Hi Kirtan
MY this problem is solved, by
 string a = r.Cells[0].Value == DBNull.Value ?  r.Cells[0].Value.ToString() :"";
                string b = r.Cells[1].Value == DBNull.Value ? r.Cells[1].Value.ToString() : "";
                string c = r.Cells[2].Value == DBNull.Value ?  r.Cells[2].Value.ToString():"";
                string d = r.Cells[3].Value == DBNull.Value ?  r.Cells[3].Value.ToString():"";
                string ee = r.Cells[4].Value == DBNull.Value ?r.Cells[4].Value.ToString():"";

problem was that i was passing null values.


ya i m using checkboxs cell[3]......13 are check boxes i want to fill present or absent according to these check boxes
so how can i check that the checkbox is checked or not?

againg same error : Object reference not set to an instance of an object.
error occure when assigning string  a=  r.cell[0].value.tostring();

 private void button1_Click(object sender, EventArgs e)
        {
            con.Open();
            DataSet ds = new DataSet();
            foreach(DataGridViewRow r in dataGridView1.Rows)
            {
                string a = r.Cells[0].Value.ToString();
                string b = r.Cells[1].Value.ToString();
                string c = r.Cells[2].Value.ToString();
                string d = r.Cells[3].Value.ToString();
                string ee = r.Cells[4].Value.ToString();
                string f = r.Cells[5].Value.ToString();
                string g = r.Cells[6].Value.ToString();
                string h = r.Cells[7].Value.ToString();
                string i = r.Cells[8].Value.ToString();
                string j = r.Cells[9].Value.ToString();
                string k = r.Cells[10].Value.ToString();
                string l = r.Cells[11].Value.ToString();
                string m = r.Cells[12].Value.ToString();
                string n = r.Cells[13].Value.ToString();
                string o = r.Cells[14].Value.ToString();
                SqlCommand cmd = new SqlCommand("insert into Student_Attendance_Record values(@a,@b,@c,@d,@ee,@f,@g,@h,@i,@j,@k,@l,@m,@n,@o", con);
                cmd.Parameters.AddWithValue("@a",a);
                cmd.Parameters.AddWithValue("@b",b);
                cmd.Parameters.AddWithValue("@c",c);
                cmd.Parameters.AddWithValue("@d",d);
                cmd.Parameters.AddWithValue("@ee",ee);
                cmd.Parameters.AddWithValue("@f",f);
                cmd.Parameters.AddWithValue("@g",g);
                cmd.Parameters.AddWithValue("@h",h);
                cmd.Parameters.AddWithValue("@i",i);
                cmd.Parameters.AddWithValue("@j",j);
                cmd.Parameters.AddWithValue("@k",k);
                cmd.Parameters.AddWithValue("@l",l);
                cmd.Parameters.AddWithValue("@m",m);
                cmd.Parameters.AddWithValue("@n",n);
                cmd.Parameters.AddWithValue("@o",o);
                //SqlCommand cmd=new SqlCommand("insert into Student_Attendance_Record values('"+r.Cells[0].Value.ToString()+"','"+r.Cells[1].Value.ToString()+"','"+r.Cells[2].Value.ToString()+"','"+r.Cells[3].Value.ToString()+"','"+r.Cells[4].Value.ToString()+"','"+r.Cells[5].Value.ToString()+"','"+r.Cells[6].Value.ToString()+"','"+r.Cells[7].Value.ToString()+"','"+r.Cells[8].Value.ToString()+"','"+r.Cells[9].Value.ToString()+"','"+r.Cells[10].Value.ToString()+"','"+r.Cells[11].Value.ToString()+"','"+r.Cells[12].Value.ToString()+"','"+r.Cells[13].Value.ToString()+"','"+r.Cells[14].Value.ToString()+"'",con);
                cmd.ExecuteNonQuery();
            }
            
            con.Close();
        }

 private void button1_Click(object sender, EventArgs e)
        {
            con.Open();
            DataSet ds = new DataSet();
            foreach(DataGridViewRow r in dataGridView1.Rows)
            {
                SqlCommand cmd=new SqlCommand("insert into Student_Attendance_Record values('"+r.Cells[0].Value.ToString()+"','"+r.Cells[1].Value.ToString()+"','"+r.Cells[2].Value.ToString()+"','"+r.Cells[3].Value.ToString()+"','"+r.Cells[4].Value.ToString()+"','"+r.Cells[5].Value.ToString()+"','"+r.Cells[6].Value.ToString()+"','"+r.Cells[7].Value.ToString()+"','"+r.Cells[8].Value.ToString()+"','"+r.Cells[9].Value.ToString()+"','"+r.Cells[10].Value.ToString()+"','"+r.Cells[11].Value.ToString()+"','"+r.Cells[12].Value.ToString()+"','"+r.Cells[13].Value.ToString()+"','"+r.Cells[14].Value.ToString()+"'",con);
                cmd.ExecuteNonQuery();
            }
            
            con.Close();
        }

this is also giveing error

in the code which give error is working when i replace
" + dataGridView1.Rows[i].Cells[5].Value.ToString() + "   with some simple string like    values('abc','aaa',........

But the below code working

 private void dataGridView1_CellEndEdit(object sender, DataGridViewCellEventArgs e)
        {
            Retrive_Data rd = new Retrive_Data();
            SqlConnection con = new SqlConnection("Data Source =.\\SQLEXPRESS;Initial Catalog = schoolmgt; password=; Integrated Security = true;");

            con.Open();
            DataSet ds = new DataSet();
            SqlDataAdapter da = new SqlDataAdapter("Retrive_S_AD1_DTL_Individual", con);

            da.SelectCommand.CommandType = CommandType.StoredProcedure;
            int i = 0;
            for (i = 0; i <= rd.Retrive_S_Exams_Marks_Class_Detail(comboBox1.Text, comboBox2.Text, comboBox3.Text).Tables["Marks"].Rows.Count - 1; i++)
            {
                SqlDataAdapter da1 = new SqlDataAdapter("Update Student_Exams_Marks_Detail set Paper1='" + dataGridView1.Rows[i].Cells[5].Value.ToString() + "', Paper2='" + dataGridView1.Rows[i].Cells[6].Value.ToString() + "',Paper3='" + dataGridView1.Rows[i].Cells[7].Value.ToString() + "',Paper4='" + dataGridView1.Rows[i].Cells[8].Value.ToString() + "',Paper5='" + dataGridView1.Rows[i].Cells[9].Value.ToString() + "',Paper6='" + dataGridView1.Rows[i].Cells[10].Value.ToString() + "',Paper7='" + dataGridView1.Rows[i].Cells[11].Value.ToString() + "',Paper8='" + dataGridView1.Rows[i].Cells[12].Value.ToString() + "',Paper9='" + dataGridView1.Rows[i].Cells[13].Value.ToString() + "',Paper10='" + dataGridView1.Rows[i].Cells[14].Value.ToString() + "' Where Regno=" + dataGridView1.Rows[i].Cells[0].Value.ToString() + "and Exam='" + dataGridView1.Rows[i].Cells[4].Value.ToString() + "'", con);
                da1.Fill(ds);
              
            }
            con.Close();
            //dataGridView1.DataSource = rd.Retrive_S_Exams_Marks_Detail(comboBox1.Text, comboBox2.Text, comboBox3.Text).Tables["Marks"];
        }

So why this working ?

i m using following code

con.Open();
            DataSet ds = new DataSet();
            for (int i = 0; i <= dataGridView1.Rows.Count-1; i++)
            {
                SqlDataAdapter da0 = new SqlDataAdapter("insert into Student_Attendance_Record values('" + dataGridView1.Rows[i].Cells[0].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[1].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[2].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[3].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[4].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[5].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[6].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[7].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[8].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[9].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[10].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[11].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[12].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[13].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[14].Value.ToString() + "',)", con);
                da0.Fill(ds);
            }
           
            con.Close();


but it give error:-Object reference not set to an instance of an object.
why?

Hi friend,

Here is Method how to do code to solve this type of problem

for example we have dataGridView Filled with two columns ( username ,password)

and also having Table Users with column (username,password) in database

now lets seee how to fill dataGridView data in database .

friend if it helps you please check "Do you like this answer" :)

You tell me about fill datagridview to database table .
But i want to update database table through datagridview data.

Hello,

I think all what you have to do is to bind data table to data grid view...

you can find below code sample:

      private void Form1_Load(object sender, System.EventArgs e){
         string connString = "server=(local)\\SQLEXPRESS;database=MyDatabase;Integrated Security=SSPI";

         string sql = @"select * from employee";

         SqlConnection conn = new SqlConnection(connString);
         SqlDataAdapter da = new SqlDataAdapter(sql, conn);
         DataSet ds = new DataSet();
         da.Fill(ds, "customers");

         // Bind the data table to the data grid
         dataGrid1.SetDataBinding(ds, "customers");

and you can refer to this link :
http://msdn.microsoft.com/en-us/library/fbk67b6z.aspx

Thanks,