在按钮单击时从sql逐个获取数据

Question

我是C#的新手。我正在开发一个 C# Windows 表单应用程序，我正在进行一个进行桌面应用程序的考试......我制作了一个表格来显示多项选择题。我希望当我单击下一步按钮时，每个问题都能从 sql 数据库中一一显示......我尝试通过以下代码执行此操作，但它不起作用...

我的代码是这样的：

 private void btnNext_Click(object sender, EventArgs e)
    {         
        SqlConnection connnn = new SqlConnection();
        connnn.ConnectionString = "Data Source=FAIZANTRADERS;Initial Catalog=ExaminationSystem;Integrated Security=True";
        connnn.Open();
        SqlDataAdapter sda = new SqlDataAdapter("SELECT isnull (min (cast (Q_ID as int)),0)+1 from CIT_Qs", connnn);
        DataTable dt = new DataTable();
        sda.Fill(dt);
        Q_idTxt.Text = dt.Rows[0][0].ToString();
        connnn.Close();
        DisplayQs();// for calling method
    }

这是表单的屏幕截图：

表单截图

Answer 1

以下是概念性的（请注意，检索到的数据并不重要，因为用于获取下一项的方法），请参阅其中的注释。

using System.Data.SqlClient;
using System.Data;
namespace WindowsFormsApplication3
{
    public class Operations
    {
        string ConnectionString = "Data Source=KARENS-PC;" + 
                "Initial Catalog=ForumExamples;Integrated Security=True";
        public DataTable Read()
        {
            DataTable dt = new DataTable();
            // add column so we can get one row/field on each button click
            dt.Columns.Add(new DataColumn() { ColumnName = "Used", DataType = typeof(bool) });
            using (SqlConnection cn = new SqlConnection { ConnectionString = ConnectionString })
            {
                using (SqlCommand cmd = new SqlCommand { Connection = cn })
                {
                    cmd.CommandText = "SELECT FullName FROM People";
                    cn.Open();
                    dt.Load(cmd.ExecuteReader());
                }
            }
            // by default the column we added, the value is null so set it to false
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                dt.Rows[i].SetField<bool>("Used", false);
            }
            return dt;
        }
    }
}

表单代码

using System;
using System.Data;
using System.Linq;
using System.Windows.Forms;
namespace WindowsFormsApplication3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        // private DataTable to work with in button1 
        DataTable dtDemo;
        // create an instance of our data class, use it in button1
        Operations ops = new Operations();
        private void button1_Click(object sender, EventArgs e)
        {
            var result = dtDemo.AsEnumerable().FirstOrDefault(row => row.Field<bool>("Used") == false);
            // find first row that is available
            if (result != null)
            {
                Console.WriteLine(result.Field<string>("FullName"));
                // mark it as used
                result.SetField<bool>("Used", true);
            }
            else
            {
                Console.WriteLine("Done"); // we have used all rows
            }
        }
        /// <summary>
        /// Load our data
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Form1_Load(object sender, EventArgs e)
        {
            dtDemo = ops.Read();
        }
    }
}