設置下拉列表的值

Question

我的任務有些問題。當我在這裏編輯數據時，我嘗試爲GridView中的dropdownlist設置值。但是當我將作業發送給我的朋友時，他告訴我他可以無誤地運行它（他使用Visual Studio 2010）。我使用Visual Studio 2008和2010，但我無法運行我的代碼。請幫幫我。

SqlConnection cn=new SqlConnection(System.Web.Configuration.WebConfigurationManager.ConnectionStrings["cn"].ToString()); 
protected void Page_Load(object sender, EventArgs e) 
{ 
    if (IsPostBack == false) 
    { 
     LoadProduct(); 
    } 
} 
public DataSet LoadCategory() 
{ 
    SqlDataAdapter da = new SqlDataAdapter("select * from categories", cn); 
    DataSet ds = new DataSet(); 
    da.Fill(ds); 
    return ds; 
} 
private void LoadProduct() 
{ 
    //throw new NotImplementedException(); 
    SqlDataAdapter da=new SqlDataAdapter("select * from products,categories where products.categoryID=categories.categoryID",cn); 
    DataTable db=new DataTable(); 
    da.Fill(db); 
    GridView1.DataSource=db; 
    GridView1.DataBind(); 
} 

protected void GridView1_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e) 
{ 
    GridView1.EditIndex = -1; 
    LoadProduct(); 
} 
protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e) 
{ 
    Literal ltr=GridView1.Rows[e.NewEditIndex].FindControl("Literal1") as Literal; 
    string categoryname = ltr.Text; 
    GridViewRow row=GridView1.Rows[e.NewEditIndex]; 
    LoadProduct(); 
    DropDownList ddl = row.Cells[3].Controls[1] as DropDownList; 
    ddl.DataSource = LoadCategory().Tables[0];// when I run there is a error. "Object reference not set to an instance of an object" 
    ddl.DataTextField = "categoryName"; 
    ddl.DataValueField = "categoryID"; 
    ddl.DataBind(); 
    ddl.Items.FindByText(categoryname).Selected = true;   
} 

Answer 1

難道你不能像這樣找到你的DDL嗎？

DropDownList ddl = GridView1.Rows[e.NewEditIndex].FindControl("ddl") as DropDownList; 
ddl.DataSource = LoadCategory().Tables[0]; 

Answer 2

試試這個

ddl.ClearSelection(); 
ddl.Items.FindByText(categoryname).Selected = true;