如何仅使用一种方法来填充ComBobox和ListBox的项目？

Question

下面的此过程用数据库中的值填充组合框。

还有一个用于ListBoxes，它是完全相同，除了“ box”是一个ListBox。

CB和LB这两个类都具有Items，并且都继承了没有Item的ListControl。

如何摆脱那里的重复代码？

private void UpdateBox (ComboBox box, string select, string from, string order = "")
{
    using (SqlConnection conn = new SqlConnection(connectionString))
    {
        conn.Open();
        if (order == "") order = select;
        using (SqlCommand command = new SqlCommand("SELECT " + select +
            " FROM " + from + " ORDER BY " + order, conn))
        {
            SqlDataReader dataReader = command.ExecuteReader();
            box.Items.Clear();
            while (dataReader.Read())
            {
                box.Items.Add(dataReader[select]);
            }
        }
    }
}

这里是另一个：

private void UpdateBox (ListBox box, string select, string from, string order = "")
{
    using (SqlConnection conn = new SqlConnection(connectionString))
    {
        conn.Open();
        if (order == "") order = select;
        using (SqlCommand command = new SqlCommand("SELECT " + select +
            " FROM " + from + " ORDER BY " + order, conn))
        {
            SqlDataReader dataReader = command.ExecuteReader();
            box.Items.Clear();
            while (dataReader.Read())
            {
                box.Items.Add(dataReader[select]);
            }
        }
    }
}

Answer 1

两个项目集合都实现IList

因此，不必传递ComboBox / ListBox，您只需传递comboBox1.Items或listBox1.Items到您的方法即可。

 private void UpdateBox (IList items, string select, string from, string order = "")

...

 items.Clear();
 while (dataReader.Read())
 {
     items.Add(dataReader[select]);
 }

Answer 2

您可以使用@Holger答案。

对于速度性能，您可以使用重构的：

private void PopulateItems(List<IList> listItems,
                           string clauseSelect,
                           string clauseFrom,
                           string clauseOrder = "")
{
  using ( var connection = new SqlConnection(connectionString) )
  {
    connection.Open();
    if ( clauseOrder == "" )
      clauseOrder = clauseSelect;
    string sql = $"SELECT {clauseSelect} FROM {clauseFrom} ORDER BY {clauseOrder}";
    using ( var command = new SqlCommand(sql, connection) )
    {
      var reader = command.ExecuteReader();
      foreach ( var items in listItems )
        items.Clear();
      while ( reader.Read() )
        foreach ( var items in listItems )
          items.Add(reader[clauseSelect]);
    }
  }
}

用法：

var listItemsToPopulate = new List<IList>()
{
  comboBox1.Items,
  listBox1.Items
};

PopulateLists(listItemsToPopulate, "", "", "");