Question

我已经尝试了一段时间了，我真的不明白。我发现错误“无法将类型'void'隐式转换为'string'” 我尝试了多种字符串变体，int，nothing，void，public，static和nope我真的不对。

我想通过我的DAL和BLL从我的db中获取一个值，我的代码看起来像这样。

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Repeater1.DataSource = BLL.getGames();
        Repeater1.DataBind();
        var culture = CultureInfo.GetCultureInfo("sv-SE");
        var dateTimeInfo = DateTimeFormatInfo.GetInstance(culture);
        var dateTime = DateTime.Today;
        int weekNumber = culture.Calendar.GetWeekOfYear(dateTime, dateTimeInfo.CalendarWeekRule, dateTimeInfo.FirstDayOfWeek);
        string mroundY = dateTime.Year.ToString();
        string mroundW = weekNumber.ToString();
        string mrounddate = mroundY + mroundW;

        string mround = BLL.getMroundGames(mrounddate);  <-- Here's the error

    }
    protected void Repeater1_ItemCommand(object source, RepeaterCommandEventArgs e)
    {

    }
}

我的BLL看起来像这样;

    public class BLL
{
    public static void getMroundGames(string mrounddate)
    {
        SqlCommand getMroundGames = new SqlCommand("SELECT mround FROM gameTB where mround = @mrounddate");
        DAL.ExecuteNonQuery(getMroundGames);
     }
}

也尝试了这个;

public class BLL
{
    public static DataTable getMroundGames(string mrounddate)
    {
        SqlCommand getMroundGames = new SqlCommand("SELECT mround FROM gameTB where mround = @mrounddate");
        getMroundGames.Parameters.Add("@mrounddate", SqlDbType.VarChar, 10).Value = mrounddate;
        return DAL.GetData(getMroundGames);
    }
}

最终我的DAL看起来像这样;

public class DAL
    {
    public static SqlConnection GetConnection()
        {
            SqlConnection conn = new
            SqlConnection(ConfigurationManager.ConnectionStrings["tiptopConnectionString"].ConnectionString);
            conn.Open();
            return conn;
        }

    public static DataTable GetData(SqlCommand command)
    {
        try
        {
            using (SqlConnection conn = GetConnection())
            {
                using (DataSet ds = new DataSet())
                {
                    using (SqlDataAdapter da = new SqlDataAdapter())
                    {
                        da.SelectCommand = command;
                        da.SelectCommand.Connection = conn;
                        da.Fill(ds);
                        return ds.Tables[0];
                    }
                }
            }
        }
        catch (Exception err)
        {
            throw new ApplicationException(string.Format("Felmeddelande:{0}", err.Message));
        }
    }

    public static object ExecuteScalar(SqlCommand command)
    {
        using (SqlConnection conn = GetConnection())
        {
            command.Connection = conn;
            object result = command.ExecuteScalar();
            return result;
        }
    }

    public static void ExecuteNonQuery(SqlCommand command)
    {
        using (SqlConnection conn = GetConnection())
        {
            command.Connection = conn;
            command.ExecuteNonQuery();
        }
    }

}

从哪里开始？

Answer 1

签名是错误的;

public static void getMroundGames(string mrounddate)

您需要将其更改为类似的内容;

public static string getMroundGames(string mrounddate)

从DAL中检索字符串值并相应地返回给使用者。

var dt = Dal.GetData();
return (string)dt.Rows[0]["field"];

但是，老实说，我不会将数据表从您的DAL传递给您的BLL。我会直接返回字符串或引入DTO并通过您的BLL将其填入DAL，然后再回传给消费者。

Answer 2

您需要为getMroundGameas（string mrounddate）添加返回类型的字符串。

目前尚不清楚DAL的对象类型，但您也应该使用ExecuteReader方法，http://msdn.microsoft.com/en-us/library/bb344397.aspx 而不是ExecuteNonQuery。这将返回一个Reader，可以查询select语句返回的值。

最后你应该返回值。

无法将类型'void'隐式转换为'string'

2 个答案: