c# - 后面的ienumerable trought代码如何实现？

Question

我想在我的代码中实现 ienumerable 以便它是只读的，但我不知道在哪里可以实现它。到目前为止，我还没有在互联网上找到任何可以解决我的问题的解决方案。截至目前，我只使用过 List 并想将 ienumerable 集成到我的代码中。此外，如果您发现不良的编码做法，请随时提出任何建议。

我试过了

public static List<GuitarItems> GetGuitarItems(string itemCategory)
{
    List<GuitarItems> list = new List<GuitarItems>();
    string query = string.Format("SELECT * FROM guitarItems WHERE brand LIKE @brand");

    try
    {
        conn1.Open();
        command1.CommandText = query;
        command1.Parameters.Add(new SqlParameter("brand", itemCategory));
        SqlDataReader reader = command1.ExecuteReader();

        while (reader.Read())
        {
            int id = reader.GetInt32(0);
            string type = reader.GetString(1);
            string brand = reader.GetString(2);
            string model = reader.GetString(3);
            double price = reader.GetDouble(4);
            string itemimage1 = reader.GetString(5);
            string itemimage2 = reader.GetString(6);
            string description = reader.GetString(7);
            string necktype = reader.GetString(8);
            string body = reader.GetString(9);
            string fretboard = reader.GetString(10);
            string fret = reader.GetString(11);
            string bridge = reader.GetString(12);
            string neckpickup = reader.GetString(13);
            string bridgepickup = reader.GetString(14);
            string hardwarecolor = reader.GetString(15);

            GuitarItems gItems = new GuitarItems(id, type, brand, model, price, itemimage1, itemimage2, description, necktype, body,
                fretboard, fret, bridge, neckpickup, bridgepickup, hardwarecolor);
            list.Add(gItems);
        }
    }
    finally
    {
        conn1.Close();
        command1.Parameters.Clear();
    }

    return list;
}

和

private void FillPage()
{
    List<GuitarItems> itemList = new List<GuitarItems>();
    List<string> itemListPage = new List<string>();

    itemList = ConnectionClassGuitarItems.GetGuitarItems(brandType);

    StringBuilder sb = new StringBuilder();

    foreach (GuitarItems gList in itemList)
    {
        itemListPage.Add("GuitarItemsIbanezDetails" + (x + 1) + ".aspx");

        sb.Append(
                string.Format(
                    @"
                    <div class='one-two'>
                        <a href='{3}' runat="'server'"><img runat="'server'" src='{0}'/></a>
                        <div class='content'>
                            <div id='label'>{1} {2}</div>
                        </div>

                </div>", gList.ItemImage1, gList.Brand, gList.Model, itemListPage[x]));

        x++;

    }

Answer 1

尝试使用迭代器方法:

public static IEnumerable<GuitarItems> GetGuitarItems(string itemCategory)
{
    using (var con = new SqlConnection("..."))
    using (var cmd = new SqlCommand("SELECT * FROM guitarItems WHERE brand LIKE @brand", con))
    {
        cmd.Parameters.AddWithValue("@brand", itemCategory);`

        con.Open();
        using (var reader = cmd.ExecuteReader(CommandBehavior.CloseConnection))
        {
            while (reader.Read())
            {
                int id = reader.GetInt32(0);
                ...

                yield return new GuitarItems(id, ...);
            }
        }
    }
}