如何在没有数据库的情况下从gridview中删除;在调用方法之前检查确定对象是否为空

是我的。cs文件中的代码

private void BindGridview(int rowcount)
{
   DataTable dt = new DataTable();
   DataRow dr;
   dt.Columns.Add(new System.Data.DataColumn("Code", typeof(String)));
   dt.Columns.Add(new System.Data.DataColumn("Course", typeof(String)));
   dt.Columns.Add(new System.Data.DataColumn("Credit", typeof(String)));
   if (ViewState["CurrentData"] != null)
   {
      for (int i = 0; i < rowcount + 1; i++)
      {
         dt = (DataTable)ViewState["CurrentData"];
         if (dt.Rows.Count > 0)
         {
            dr = dt.NewRow();
            dr[0] = dt.Rows[0][0].ToString();
         }
      }
      dr = dt.NewRow();
      dr[0] = this.cboCourseCode.Text;
      dr[1] = this.txtCourseName.Text;
      dr[2] = this.txtCredit.Text;
      dt.Rows.Add(dr);
   }
   else
   {
      dr = dt.NewRow();
      dr[0] = this.cboCourseCode.Text;
      dr[1] = this.txtCourseName.Text;
      dr[2] = this.txtCredit.Text;
      dt.Rows.Add(dr);
   }
   // If ViewState has a data then use the value as the DataSource
   if (ViewState["CurrentData"] != null)
   {
      GridView1.DataSource = (DataTable)ViewState["CurrentData"];
      GridView1.DataBind();
   }
   else
   {
      // Bind GridView with the initial data assocaited in the DataTable
      GridView1.DataSource = dt;
      GridView1.DataBind();
   }
   // Store the DataTable in ViewState to retain the values
   ViewState["CurrentData"] = dt;
}
protected void BindGrid()
{
   GridView1.DataSource = ViewState["dt"] as DataTable;
   GridView1.DataBind();
}
protected void OnRowDeleting(object sender, GridViewDeleteEventArgs e)
{
   int index = Convert.ToInt32(e.RowIndex);
   DataTable dt = ViewState["dt"] as DataTable;
   dt.Rows[e.RowIndex].Delete();
   ViewState["dt"] = dt;
   BindGrid();
}
protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
{
   if (e.Row.RowType == DataControlRowType.DataRow)
   {
      string Code = e.Row.Cells[0].Text;
      foreach (Button button in e.Row.Cells[3].Controls.OfType<Button>())
      {
         if (button.CommandName == "Delete")
         {
            button.Attributes["onclick"] = "if(!confirm('Do you want to delete " + Code + "?')){ return false; };";
         }
      }
   }   
}         
protected void cboCourseCode_SelectedIndexChanged(object sender, EventArgs e)
{
   this.Populate_Course_Details();
}
protected void BtnAdd_Click(object sender, EventArgs e)
{
   /*  DataTable dt = new DataTable();
   dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Code"), new DataColumn("Course"), new DataColumn("Credit") });
   dt.Rows.Add(this.cboCourseCode.Text, this.txtCourseName.Text, this.txtCredit.Text);           
   ViewState["dt"] = dt;
   BindGrid();*/
   if (ViewState["CurrentData"] != null)
   {
      DataTable dt = (DataTable)ViewState["CurrentData"];
      int count = dt.Rows.Count;
      BindGridview(count);
   }
   else
   {
      BindGridview(1);
   }
}

我的aspx文件也有这个gridview

<asp:GridView ID="GridView1" CssClass = "Grid" runat="server" OnRowDeleting="OnRowDeleting" AutoGenerateColumns = "false" OnRowDataBound = "OnRowDataBound">
    <Columns>
        <asp:BoundField DataField="Code" HeaderText="Code" />
        <asp:BoundField DataField="Course" HeaderText="Course" />
        <asp:BoundField DataField="Credit" HeaderText="Credit" />
        <asp:CommandField ShowDeleteButton="True" ButtonType="Button" />
    </Columns>
</asp:GridView>

当我开始删除，我得到这个错误:

在调用

方法之前检查对象是否为空