为什么我DATAGRIDVIEW里不能写入数据？

Question

把鼠标移到下个单元格上个单元格的值就没了？
  public AddPlan()
        {
            InitializeComponent();
                     this.dataGridView2.EditMode = System.Windows.Forms.DataGridViewEditMode.EditOnEnter;
            dataGridView2.AllowUserToAddRows = true;
        }
   private void btn_tj_Click(object sender, EventArgs e)
        {
            
            int index2 = 0;
            int index3 = 1;
            int index4 = 2;
            int index5 = 3;
            int index6 = 4;
            int index7 = 5;
            int index8 = 6;
            int index9 = 7;
            string num = dataGridView2[index2, dataGridView2.SelectedCells[0].RowIndex].Value.ToString();
            string name = dataGridView2[index3, dataGridView2.SelectedCells[0].RowIndex].Value.ToString();
            string count = dataGridView2[index4, dataGridView2.SelectedCells[0].RowIndex].Value.ToString();
            string model = dataGridView2[index5, dataGridView2.SelectedCells[0].RowIndex].Value.ToString();
            string kwm = dataGridView2[index6, dataGridView2.SelectedCells[0].RowIndex].Value.ToString();
            string gys = dataGridView2[index7, dataGridView2.SelectedCells[0].RowIndex].Value.ToString();
            string bz = dataGridView2[index8, dataGridView2.SelectedCells[0].RowIndex].Value.ToString();
            string people = dataGridView2[index9, dataGridView2.SelectedCells[0].RowIndex].Value.ToString();
            string temp1 = string.Format("insert into T_Purchasing(T_Number,T_Name,T_Quantity,T_Model,T_DepotName,T_SupplierName,T_Re,T_Principal,T_date) values('" + num + "','" + name + "'," + Int32.Parse(count) + ",'" + model + "','" + kwm + "','" + gys + "','" + bz + "','" + people + "')");
            DCC.SqlDC.SDC.GetTable(temp1);
            DialogResult result = MessageBox.Show("添加成功", "采购管理", MessageBoxButtons.OK, MessageBoxIcon.Asterisk);
            if (result == DialogResult.OK)
            {
                this.Close();
            }        }
 private void dataGridView2_MouseDown(object sender, MouseEventArgs e)
        {
            dataGridView2.ContextMenuStrip = contextMenuStrip1;
           
        }        private void 插入数据ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            dataGridView2.ColumnCount = 8;//定义增加列的总数  
            dataGridView2.Columns[0].Name = "物料编号";
            dataGridView2.Columns[1].Name = "所属物品";
            dataGridView2.Columns[2].Name = "数量";
            dataGridView2.Columns[3].Name = "1=成品库,2=部件库,3=零件库";
            dataGridView2.Columns[4].Name = "供应商名称";
            dataGridView2.Columns[5].Name = "备注";
            dataGridView2.Columns[6].Name = "制表人";
            dataGridView2.Columns[7].Name = "制表日期";
        }

Answer 1

 private void 插入数据ToolStripMenuItem_Click(object sender, EventArgs e)
  {
  dataGridView2.ColumnCount = 8;//定义增加列的总数   
  dataGridView2.Columns[0].Name = "物料编号";
  dataGridView2.Columns[1].Name = "所属物品";
  dataGridView2.Columns[2].Name = "数量";
  dataGridView2.Columns[3].Name = "1=成品库,2=部件库,3=零件库";
  dataGridView2.Columns[4].Name = "供应商名称";
  dataGridView2.Columns[5].Name = "备注";
  dataGridView2.Columns[6].Name = "制表人";
  dataGridView2.Columns[7].Name = "制表日期";
  }
没有增加..
这样增加列dataGridView2.Columns.Add("物料编号");

Answer 2

this.DataGridView1.CurrentCell   =   this.DataGridView1.Rows[3].Cells[2]; 
this.DataGridView1.BeginEdit(True); DataGridViewRow row = new DataGridViewRow();   
row.Cells[0].Value =dt[""].ToString();   
row.Cells[1].Value = dt[""].ToString();   
this.dataGridView1.Rows.Add(row);

Answer 3

this.DataGridView1.CurrentCell = this.DataGridView1.Rows[3].Cells[2];  
this.DataGridView1.BeginEdit(True);  DataGridViewRow row = new DataGridViewRow();   
row.Cells[0].Value =dt[""].ToString();   
row.Cells[1].Value = dt[""].ToString();   
this.dataGridView1.Rows.Add(row);