asp.net基础来一遍----数据存取

下面是对xml,access,mssql数据存取
protected DataSet LoadMyPBData()
    {
        string sourceXml = Server.MapPath("phone.xml");
        DataSet dataSet = new DataSet();
        try
        {
            dataSet.ReadXml(sourceXml);
        }
        catch (Exception e)
        {
           
            dataSet = null;
        }
        return dataSet;
    }

    void Page_Load(object sender, EventArgs e)
    {
        if (!(Page.IsPostBack))
        {
            gridv.DataSource = LoadMyPBData();
            gridv.DataBind();
        }
    }
-------------------------------
String StrSql="Data Source=127.0.0.1;Initial Catalog=dotnet;persist security info=True;user id=sa;password=1234;packet size=4096";
SqlConnection MyConn = new SqlConnection(StrSql);
MyConn.Open();
string CommSql = "select * from gbook order by id desc";
SqlDataAdapter adp = new SqlDataAdapter(CommSql,MyConn);
DataSet ds = new DataSet();
adp.Fill(ds);
DataGrid1.DataSource = ds;
DataGrid1.DataBind();
MyConn.Close();
---------------------------------------
  if(!IsPostBack) 
   {
   OleDbConnection MyConnection =new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source="+Server.MapPath("new.mdb"));  
   OleDbDataAdapter myCommand=new OleDbDataAdapter("SELECT id,typename FROM bb ",MyConnection);   
   DataSet ds= new DataSet();  
   myCommand.Fill(ds,"bb");  
   DropDownList2.DataSource = ds.Tables["bb"].DefaultView;    
   DropDownList2.DataTextField = "typename";  
   DropDownList2.DataValueField = "id";  
   DropDownList2.DataBind(); 

……