c# winform 显示组合框选择的数据库数据

Question

我有一个复选按钮，可以在组合框中获取月份和年份:

private void cmdSend_Click(object sender, System.EventArgs e)
    {
        List<string>[] list;
        list = dbConnect.Select(month_list.SelectedItem.ToString(), year_list.SelectedItem.ToString());

        printer_info.Rows.Clear();
        for (int i = 0; i < list[0].Count; i++)
        {
            int number = printer_info.Rows.Add();
            printer_info.Rows[number].Cells[0].Value = list[0][i];
            printer_info.Rows[number].Cells[1].Value = list[1][i];
            printer_info.Rows[number].Cells[2].Value = list[2][i];
            printer_info.Rows[number].Cells[3].Value = list[3][i];
        }
    }  

检查按钮然后将月份和年份传递给选择语句函数:

public List<string>[] Select(string month,string year)
    {
        string query = "SELECT * FROM page_counter WHERE month = '@month' AND year = @year;";

        //Create a list to store the result
        List<string>[] list = new List<string>[4];
        list[0] = new List<string>();
        list[1] = new List<string>();
        list[2] = new List<string>();
        list[3] = new List<string>();

        //Open connection
        if (this.OpenConnection() == true)
        {
            //Create Command
            MySqlCommand cmd = new MySqlCommand(query, connection);
            cmd.Parameters.Add("@month",MySqlDbType.VarChar);
            cmd.Parameters.Add("@year", MySqlDbType.Year);
            cmd.Parameters["@month"].Value = month;
            cmd.Parameters["@year"].Value = year;

            //Create a data reader and Execute the command
            MySqlDataReader dataReader = cmd.ExecuteReader();

            //Read the data and store them in the list
            while (dataReader.Read())
            {
                list[0].Add(dataReader["id"].ToString() + "");
                list[1].Add(dataReader["month"].ToString() + "");
                list[2].Add(dataReader["year"].ToString() + "");
                list[3].Add(dataReader["page_count"].ToString() + "");
            }

            //close Data Reader
            dataReader.Close();

            //close Connection
            this.CloseConnection();

            //return list to be displayed
            return list;
        }  

数据将显示在 GridView 上，其中所有列在页面设计器中默认指定:

当我运行代码时，它没有任何错误，但 GridView 上没有显示任何值。我有什么错误吗？我是c# winform新手，请指教。

Answer 1

我认为你有两个错误。首先你应该删除 single-quotes来自查询字符串:

string query = "SELECT * FROM page_counter WHERE month = @month AND year = @year;"

因为当您使用单引号时，您的参数名称将被视为实际值。其次，我强烈建议您为您的项目使用类，而不是 List<string>[] .类看起来像这样:

public class Data
{
    public int Id { get; set; }
    public string Month { get; set; }
    public string Year { get; set; }
    public int PageCount { get; set; }
}

然后创建一个List<Data>并像这样填充它:

 var dataList = new List<Data>();
 while (dataReader.Read())
 {
    var item = new Data();
    item.Id = Convert.Toınt32(dataReader["id"]);
    item.Month = dataReader["month"].ToString();
    item.Year = dataReader["year"].ToString();
    item.PageCount = Convert.ToInt32(dataReader["page_count"]);
    dataList.Add(item);
}
return dataList;

然后当然要更改方法的返回类型:

public List<Data> Select(string month,string year)

那么您需要做的就是设置 DataSource属性:

var list = dbConnect.Select(month_list.SelectedItem, year_list.SelectedItem);
printer_info.DataSource = list;