c# - DropDownList 重复项

Question

嗨，我正在尝试将数据重新绑定到DataList从中获取数据的数据，SqlDataSource但我不断收到重复的项目。这是我的代码：

<asp:SqlDataSource ID="CategoryDataSource" runat="server" 
    ConnectionString="Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\ASPNETDB.MDF;Integrated Security=True;User Instance=True" 
    ProviderName="System.Data.SqlClient" SelectCommand="SELECT [CategoryName] FROM [forum_categories]">
</asp:SqlDataSource>

protected void Button6_Click( object sender , EventArgs e )
{
    string categoryToCreate = CreateCategory.Text;

    if(categoryToCreate != string.Empty)
    {
        CategoryCreateName.Visible = false;
        DataAccess.insertDataItem(categoryToCreate);
        CategoryList.DataBind(); 
    }
    else
    {
        CategoryCreateName.Visible = true;
    }
}

insertDataItem将一个新类别插入到数据库中。

如何更新中的项目，DropDownList以免我得到重复的项目？

Answer 1

尝试这个：

    protected void Button6_Click( object sender , EventArgs e )
{
    string categoryToCreate = CreateCategory.Text;

    if(categoryToCreate != string.Empty)
    {
        CategoryCreateName.Visible = false;
        DataAccess.insertDataItem(categoryToCreate);
        CategoryList.Items.Clear();
        CategoryList.DataBind(); 
    }else
    {
        CategoryCreateName.Visible = true;
    }
}