如何选择和读取下拉列表中的数据? [英] how to select and read data in dropdownlist?

问题描述

你好.
我打算将我的dropdownlist绑定到sqlserver，并读取我在DB(Table City)中拥有的项目(CityName)，然后列出并将其填充到dropdownlist中.
为此，我在Page_load中编写了以下代码，每当我开始调试所有要在dropdownlist中看到的城市项目时，该代码就会显示:

hello.
I intend to bind my dropdownlist to sqlserver and read the items(CityName)that i have them in DB(Table City)and then list and fill them into the dropdownlist.
for this matter i have written the code below in Page_load that whenever i start to debug all city items to be seen in dropdownlist:

protected void Page_Load(object sender, EventArgs e)
       {
           SqlConnection conn = new SqlConnection();
           SqlCommand cmd = new SqlCommand();
           conn.ConnectionString = ConfigurationManager.ConnectionStrings["PersonTest"].ConnectionString;

           conn.Open();
           cmd.CommandText = "SELECT CityName FROM City";
           cmd.Parameters.Add("@CityName", SqlDbType.NVarChar).Value = DropCity.AppendDataBoundItems;
           cmd.ExecuteReader();
           conn.Close();
       }

但在(cmd.ExecuteReader();)行中会发生此错误:

InvalidOperationException未由用户代码处理.
ExecuteReader:连接属性尚未初始化

同时，我知道我可以使用ASP.net DataBinding(通过向导)功能，但是我想自己动手做.而且我也不知道哪种形式更适合使用?您建议使用哪一个?

but in line (cmd.ExecuteReader();) this error occurs:

InvalidOperationException was unhandled by user code.
ExecuteReader: Connection property has not been initialized

meanwhile i know that i can use ASP.net DataBinding(by wizard)ability, but i want to do it with myself . and also i don''t know which one is better to be used in forms? which one do you suggest to use?

推荐答案

您可以使用它来将数据绑定到您的下拉列表

Hi ,
you can use this for bind data to your dropdownlist

if (!IsPostBack)
    {
        using (SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["PersonTest"].ConnectionString))
        {
            conn.Open();
            using (SqlCommand cmd = new SqlCommand("SELECT CityName , id FROM City", conn))
            {
                DataTable dt = new DataTable();
                SqlDataAdapter adpt = new SqlDataAdapter(cmd);
                adpt.Fill(dt);
                DropCity.DataTextField = "CityName";
                DropCity.DataValueField = "id";
            }
        } 
    }

并选择下拉列表的值，您可以使用SelectedValue
最好的问候
米特瓦里(M.Mitwalli)

and for select the value of dropdownlist you can use SelectedValue
Best Regards
M.Mitwalli

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