C# Datagridview 控件增删改后点击保存按钮 但是显示错误上下文中不存在名称dt

    private void button1_Click(object sender, EventArgs e)
    {
        if (textBox1.Text == "")
        {
            MessageBox.Show("提示：用户名不能为空！");
        }
        else
        {
            SqlConnection conn = new SqlConnection("Data Source=.;Initial Catalog=User;Integrated Security=True");
            conn.Open();
            SqlDataAdapter allTableAdapter  = new SqlDataAdapter("select* from total where ID LIKE '" + textBox1.Text.Trim() + "%'",conn);
            DataSet ds = new DataSet();
            allTableAdapter.Fill(ds,"tota");
            //将获取的数据填充到数据集ds中
            //数据源绑定到dataGridView
            DataTable dt = ds.Tables["tota"];
            dataGridView1.DataSource = dt.DefaultView;
            conn.Close();    
        }
    }

    private void button2_Click(object sender, EventArgs e)
    {
        
        SqlConnection conn = new SqlConnection("Data Source=.;Initial Catalog=User;Integrated Security=True");
        conn.Open();
        DataTable changeDt = dt.GetChanges();
        foreach (DataRow dr in changeDt.Rows)
        {
            string strSQL = string.Empty;
            if (dr.RowState == System.Data.DataRowState.Added)
            {
                strSQL = @"INSERT INTO [User].[dbo].[total]
                                               ([ID]
                                               ,[PW]
                                               ,[type]
                                               ,[login])
                                         VALUES
                                               ('" + dr["ID"].ToString() + @"'
                                               ,'" + dr["PW"].ToString() + @"'
                                               ,'" + Convert.ToInt32(dr["type"]) + @"'
                                               ,'" + dr["login"].ToString() + @"')";
                SqlCommand comm = new SqlCommand(strSQL, conn);
                comm.ExecuteNonQuery();
            }
        }
    }

上面是代码，但会一直显示错误说dt不存在，这是为什么呀

需要把数据再存到dataset吗，如果非必要请sqldataadapter.fill(dt)