Question

我在Windows窗体上有一个组合框，我填写了一个名字列表。目前我在Form类中有以下代码，它可以正常工作

    // This section opens a connection to the database, selects all the portfolio names that have an "in Use" value of 1, and then
    // fills Combo Box 2 with the values. 
        SqlConnection myConnection = new SqlConnection(@"Data Source = (LocalDB)\MSSQLLocalDB; AttachDbFilename = ""C:\Users\Nick\Documents\Investments 4.mdf""; Integrated Security = True; Connect Timeout = 30");
        myConnection.Open();
        SqlCommand myCommand2 = new SqlCommand();
        myCommand2.Connection = myConnection;
        myCommand2.CommandText = "SELECT Portfolio_Name FROM Dbo.Name WHERE In_use = 1";
        SqlDataReader myReader2 = myCommand2.ExecuteReader();
        while (myReader2.Read())
        {
            comboBox2.Items.Add(myReader2[0]);
        }
        myConnection.Close();

我希望能够将其提取到一个单独的方法中，并将其放入一个单独的类中以用于通用实用方法。但是，我坚持一个非常简单的问题。当我把代码放到一个类中时，我需要能够告诉它我要填充哪个combox框，而我无法弄清楚如何传递这些信息。很抱歉，如果答案很明显，但我们将非常感谢您的帮助。

谢谢！

Answer 1

好吧，如果你想提取，那么提取：

// Let's extract a class: it should provide us standard cursors, 
// e.g. Protfolio Names 
public static class MyData {
  // Let's enumerate items returned
  public static IEnumerable<string> PortfolioNames() {
    // Wrap IDisposable into using
    //TODO: move Connection String into a separated method/property 
    using (SqlConnection con = new SqlConnection(/*connection string here*/)) {
      con.Open();

      // Make sql readable 
      //DONE: when presenting something to user, sort it (order by) esp. strings
      string sql = 
        @"  select Portfolio_Name
              from Dbo.Name
             where In_use = 1
          order by Portfolio_Name"; 

      // Wrap IDisposable into using
      using (SqlCommand q = new SqlCommand(sql, con)) {
        // Wrap IDisposable into using 
        using (var reader = q.ExecuteReader()) {
          while (reader.Read())
            yield return Convert.ToString(reader[0]);
        }
      }
    }
  }
}

然后使用

// Adding items in one after one manner is often a bad idea:
// it makes UI repaint each time you add an item and cause blinking.
// Let's fill the ComboBox in one go via AddRange  
comboBox2.Items.AddRange(MyData.PortfolioNames().ToArray());

Answer 2

您可以使用帮助程序类名Portfolio进行数据访问。方法GetNames不需要ComboBox实例。这增加了在另一个上下文中重用该方法的可能性。

public static class Portfolio
{
    public static IList<string> GetNames()
    {
        SqlConnection myConnection = new SqlConnection(@"Data Source = (LocalDB)\MSSQLLocalDB; AttachDbFilename = ""C:\Users\Nick\Documents\Investments 4.mdf""; Integrated Security = True; Connect Timeout = 30");
        myConnection.Open();
        SqlCommand myCommand2 = new SqlCommand();
        myCommand2.Connection = myConnection;
        myCommand2.CommandText = "SELECT Portfolio_Name FROM Dbo.Name WHERE In_use = 1";
        SqlDataReader myReader2 = myCommand2.ExecuteReader();
        var portfolioNames = new List<string>();
        while (myReader2.Read())
        {
            portfolioNames.Add(myReader2[0]);
        }
        myConnection.Close();
        return portfolioNames;
    }
 }

然后在你的表格中你可以做这样的事情：

var names = Portfolio.GetNames();
foreach (var name in names)
{
    combobox2.Items.Add(name);
}

Answer 3

这很简单：

public class MyUtility
{
    public static void FillComboBox(System.Windows.Forms.ComboBox comboBox)
    {
        //comboBox.Items.Clear(); //enable this line if required
        using (SqlConnection myConnection = new SqlConnection(@"Data Source = (LocalDB)\MSSQLLocalDB; AttachDbFilename = ""C:\Users\Nick\Documents\Investments 4.mdf""; Integrated Security = True; Connect Timeout = 30"))
        {
            myConnection.Open();
            using (SqlCommand myCommand2 = new SqlCommand())
            {
                myCommand2.Connection = myConnection;
                myCommand2.CommandText = "SELECT Portfolio_Name FROM Dbo.Name WHERE In_use = 1";
                using (SqlDataReader myReader2 = myCommand2.ExecuteReader())
                {
                    while (myReader2.Read())
                    {
                        comboBox.Items.Add(myReader2[0]);
                    }
                }
            }
            //myConnection.Close(); //not required inside using block
        }
    }
}

您可以使用其他方法获取连接字符串（例如，从配置文件中）。

用法非常简单，无需额外代码：

MyUtility.FillComboBox(comboBox2);

从表单中提取填充方法

3 个答案: