如何在下拉列表中获取所选项目的值？

Question

I have a drop down list populated from a database. When i use the dplTags.SelectedItem.Value it only returns the first value and not the one i selected?

Could Someone tel me where i'm going wrong?

When i call it:

String TagID = dplTags.SelectedItem.Value; // Will only select the first value????

It always returns the TagID of the first item, not the selected one :\\

This is how i bind it:

using (var conn = new SqlConnection(Properties.Settings.Default.DBConnectionString))
            {
                conn.Open();

                SqlDataAdapter daTags
                = new SqlDataAdapter("Select * From Tag", conn);

                DataSet dsTags = new DataSet("TagCloud");

                daTags.FillSchema(dsTags, SchemaType.Source, "Tag");
                daTags.Fill(dsTags, "Tag");

                daTags.MissingSchemaAction = MissingSchemaAction.AddWithKey;
                daTags.Fill(dsTags, "Tag");

                DataTable tblTag;
                tblTag = dsTags.Tables["Tag"];

                dplTags.DataSource = dsTags;
                dplTags.DataMember = "Tag"; 
                dplTags.DataValueField = "TagID"; //Value Member
                dplTags.DataTextField = "Value"; // Display Member
                dplTags.DataBind();
            }

Please help, Thanks in Advance.

Answer 1

Where are you binding data to these dropdown list controls? They should be bound only in the initial loading of the page as follows. I suspect that you are binding them in every page load and therefore selected values disappear.

protected void Page_Load(object sender, EventArgs e)
{

    if (!Page.IsPostBack)
    {
        //Please check if you are binding checkbox controls here. 
        //If not bring them in here
    }
}

Answer 2

仅当Page.IsPostback == false时，才启用页面的视图状态，并对下拉列表进行数据绑定

Answer 3

Bind the dropdown list once on first page load and do not bind it again on postback. Binding it again will fill the dropdown with new elements and previous selection will be lost.

if(!Page.IsPostBack)
{
using (var conn = new SqlConnection(Properties.Settings.Default.DBConnectionString))
            {
                conn.Open();

                SqlDataAdapter daTags
                = new SqlDataAdapter("Select * From Tag", conn);

                DataSet dsTags = new DataSet("TagCloud");

                daTags.FillSchema(dsTags, SchemaType.Source, "Tag");
                daTags.Fill(dsTags, "Tag");

                daTags.MissingSchemaAction = MissingSchemaAction.AddWithKey;
                daTags.Fill(dsTags, "Tag");

                DataTable tblTag;
                tblTag = dsTags.Tables["Tag"];

                dplTags.DataSource = dsTags;
                dplTags.DataMember = "Tag"; 
                dplTags.DataValueField = "TagID"; //Value Member
                dplTags.DataTextField = "Value"; // Display Member
                dplTags.DataBind();
            }
}