GridView不绑定数据源

Question

以下代码有什么问题？ GridView GridView1根本不在页面上显示。

public void display_range_mark() 
    { 
     int from = int.Parse(ddl_from_mark.SelectedValue.ToString()); 
     int to = int.Parse(ddl_to_mark.SelectedIndex.ToString()); 
     DataTable dt=Data.DoSomthing(string.Format("select ts.Name,ts.FamilyName,ts.Id_student,td.Name,tn.NomreAdad from tblStudent ts,tblDars td,tblNomre tn where tn.NomreAdad>='{0}' AND tn.NomreAdad<='{1}' AND ts.Id=tn.Id_student AND td.Id=tn.Id_dars",from,to)); 
     //DataTable data = Data.DoSomthing(string.Format("select t.Name,t.Id from tblStd t where t.DateSabt='{0}'", p.GetYear(DateTime.Now))); 
     GridView1.DataSource = dt; 
     GridView1.HeaderRow.Cells[0].Text = "نام"; 
     GridView1.HeaderRow.Cells[1].Text = "نام خانوادگی"; 
     GridView1.HeaderRow.Cells[2].Text = "شماره دانش آموزی"; 
     GridView1.HeaderRow.Cells[3].Text = "درس"; 
     GridView1.HeaderRow.Cells[4].Text = "نمره"; 
     GridView1.DataBind(); 



    } 

我收到此错误：
异常详细信息：System.NullReferenceException：未设置为一个对象的实例对象引用。在这条线发生 错误：

GridView1.HeaderRow.Cells[0].Text = "نام"; 

顺便说，对于Data.DoSomthing代码是作为folllows（它位于类内数据库）：

SqlConnection sc = new SqlConnection(@"Data Source=.;Initial Catalog=School;Integrated Security=True"); 



public DataTable DoSomthing(string text) 
    { 
     sc.Open(); 
     DataTable data = new DataTable(); 
     try 
     { 
      SqlCommand command = new SqlCommand(); 
      command.Connection = sc; 
      command.CommandType = CommandType.Text; 
      command.CommandText = text; 

      SqlDataAdapter sd = new SqlDataAdapter(command); 
      sd.Fill(data); 
      if (data.Rows.Count == 0) 
       data = null; 
     } 
     catch (Exception ex) 
     { 
      sc.Close(); 
      return null; 
     } 
     finally 
     { 
      if (sc.State != ConnectionState.Closed) 
      { 
       sc.Close(); 
      } 
     } 
     return data; 
    } 

Answer 1

在哪里是连接到数据库并获取值的连接对象吗？

做到这一点的方法：

string query="select ts.Name,ts.FamilyName,ts.Id_student,td.Name,tn.NomreAdad from  tblStudent ts,tblDars  td,tblNomre tn where tn.NomreAdad>=@from AND tn.NomreAdad<=@to AND ts.Id=tn.Id_student AND td.Id=tn.Id_dars"; 

//Create Sqlconnection object 
using(SqlConnection con = new SqlConnection(connectionstring)) 
{ 
//open the connection 
con.Open(); 
SqlDataAdapter sda = new SqlDataAdapter(query, con); 
//To avoid sql injection using parameters 
sda.Paramaters.AddWithValue("@from",from); 
sda.Paramaters.AddWithValue("@to",to); 
DataTable dt = new DataTable(); 
sda.Fill(dt); 
GridView1.DataSource = dt; 
GridView1.DataBind(); 
}