con = new System.Data.OleDb.OleDbConnection(sqlconnectionstr);
            con.Open();
            cmd = new System.Data.OleDb.OleDbCommand("select * from accounts", con);
            dd = new System.Data.OleDb.OleDbDataAdapter(, con);
            ds = new DataSet();
            dd.Fill(ds, "accounts");
            dataGridView1.DataSource = ds.Tables[0].DefaultView;
            dataGridView1.Columns[0].HeaderCell.Value = "账务编码";
            dataGridView1.Columns[1].HeaderCell.Value = "银行编码";
            dataGridView1.Columns[2].HeaderCell.Value = "员工编码";
            dataGridView1.Columns[3].HeaderCell.Value = "账务大类编码";
            dataGridView1.Columns[4].HeaderCell.Value = "账务小类编码";
            dataGridView1.Columns[5].HeaderCell.Value = "账务类型";
            dataGridView1.Columns[6].HeaderCell.Value = "金额";
            dataGridView1.Columns[7].HeaderCell.Value = "账务日期";
            dataGridView1.Columns[8].HeaderCell.Value = "备注";
           // MessageBox.Show(this.dataGridView1["payments", 0].Value.ToString());
            for (int k = 0; k < ds.Tables[0].Rows.Count; k++)
            {
                if (this.dataGridView1.Rows[k]["payments"].ToString() == "收入")//运行时这个给了提示未将对象引用设置到对象的实例。
                    sumin += Convert.ToDouble(this.dataGridView1["price", k].Value.ToString());
                else
                    sumout += Convert.ToDouble(this.dataGridView1["price", k].Value.ToString());
            }
            this.label9.Text = Convert.ToString(sumin - sumout);
            this.label10.Text = Convert.ToString(sumin);
            this.label11.Text = Convert.ToString(sumout);

表accounts没有payments这一列?

有这个字段payments,更晕的是加MessageBox.Show(this.dataGridView1["payments", 0].Value.ToString());他就不提示。

[ 本帖最后由 chenhao19860 于 2011-3-22 17:28 编辑 ]

LZ可以仔细检查下dataGridView是否存在名为payments这一列

肯定有payments这个字段，show都有值

楼主可以看一下，在表的设计里面，这一列是否允许出现空值
空值是不能与string比较的

终于解决了，是因为越界的问题，列数是从0开始至datagridview。rows。count-1就对了，谢谢各位的关注！

不是count-1的原因,是因为datagridview的AllowUserToAddRows被设为true而多了一个空行造成的,那行要特殊处理,DataRow为False