C# 将数据库中的数据提取到组合框及其值C中#

你好，我的数据库课上有一张桌子

在我的组合框中，我获取了class列并将其值设置为class id，但是现在当表单加载时，它只在组合框中显示JSS1，留下JSS2-SSS3

这是我的密码

SqlConnection con = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\Solutions\Desktop\My Work\ExamProject\Project DataBase File For Exam\EExamDB.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");
bool classHaveBeenAdded = false;

void ClassCombo()       
        try
        {
            con = new SqlConnection(Properties.Settings.Default.MyConnection);
            cmd = new SqlCommand("SELECT * FROM Classes", con);
            cmd.Connection.Open();
            SqlDataReader readClass = cmd.ExecuteReader();
            ArrayList ClassList = new ArrayList();
            if (readClass.Read())
            {
                ClassList.Add(new AddValue(readClass.GetString(1), readClass.GetInt32(0)));
            }
            readClass.Close();
            cmd.Connection.Close();

            this.comboBoxClassID.DataSource = ClassList;
            this.comboBoxClassID.DisplayMember = "Display";
            this.comboBoxClassID.ValueMember = "Value";
            classHaveBeenAdded = true;
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

    public class AddValue
    {
        public string m_Display;
        public int m_Value;

        public AddValue(string Display, int Value)
        {
            m_Display = Display;
            m_Value = Value;
        }

        public string Display
        {
            get { return m_Display; }
        }

        public int Value
        {
            get { return m_Value; }
        }
    }

---

您没有从数据库读取值的循环：

if (readClass.Read())
{
    ClassList.Add(new AddValue(readClass.GetString(1), readClass.GetInt32(0)));
}

应该是：

while (readClass.Read())
{
    ClassList.Add(new AddValue(readClass.GetString(1), readClass.GetInt32(0)));
}

试试这个：-

   void ClassCombo()       
    try
    {
        con = new SqlConnection(Properties.Settings.Default.MyConnection);
        cmd = new SqlCommand("SELECT * FROM Classes", con);
        cmd.Connection.Open();
        SqlDataReader readClass = cmd.ExecuteReader();
        ArrayList ClassList = new ArrayList();
        int i=0;
        while (readClass.Read())
        {
            ClassList.Add(readClass["class"].ToString());
            i++;
        }
        readClass.Close();
        cmd.Connection.Close();

        this.comboBoxClassID.DataSource = ClassList;
        this.comboBoxClassID.DisplayMember = "Display";
        this.comboBoxClassID.ValueMember = "Value";
        classHaveBeenAdded = true;
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

---

您的组合框中只有一个值？？？我没有解决它。我用if代替了一段时间；这样你就可以放弃尝试/捕获

m_显示

和

m_值

应该是私有的。参数大小写应为：

AddValue（字符串显示，int值）

。为什么使用

ArrayList

而不是通用集合，例如

List

？

   void ClassCombo()       
    try
    {
        con = new SqlConnection(Properties.Settings.Default.MyConnection);
        cmd = new SqlCommand("SELECT * FROM Classes", con);
        cmd.Connection.Open();
        SqlDataReader readClass = cmd.ExecuteReader();
        ArrayList ClassList = new ArrayList();
        int i=0;
        while (readClass.Read())
        {
            ClassList.Add(readClass["class"].ToString());
            i++;
        }
        readClass.Close();
        cmd.Connection.Close();

        this.comboBoxClassID.DataSource = ClassList;
        this.comboBoxClassID.DisplayMember = "Display";
        this.comboBoxClassID.ValueMember = "Value";
        classHaveBeenAdded = true;
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}