如何根據另一個列表框中的選定項目填充列表框？

Question

當我的表單加載時，我有兩個列表框（Regions和Divisions），“區域”列表框填充了4個區域（中西部，東北，南，西）。 當我單擊這些區域之一時，我希望“分區”列表框填充與所單擊區域相關的分區。 我正在通過與SQL db通信的數據存儲庫進行工作。 表格加載時的初始填充

StateRepository sr = new StateRepository();
foreach (string s in sr.GetRegions())
{
    lstRegions.Items.Add(s);
}

GetRegions方法背后的代碼：

public IEnumerable<string> GetRegions()
{
    try
    {
        List<string> results = new List<string>();
        using (var conn = new SqlConnection(Settings.Default.StateAnalysisConnection))
        {
            using (var cmd = conn.CreateCommand())
            {
                cmd.CommandText = "Select * From Regions ";
                conn.Open();
                using (var reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        results.Add((string)reader["Region"]);
                    }
                }
            }
         }

         return results;
    }
    catch (Exception ex)
    {
        throw new Exception("Database error in StateRepository", ex);
    }
    finally
    {
        if (connection.State == ConnectionState.Open)
            connection.Close();
    }
}

從數據庫獲取區域划分的方法：

public IEnumerable<string> GetDivisionsInRegion(string region)
{
    try
    {
        List<string> results = new List<string>();
        var divisions = new List<string>();
        using (var conn = new SqlConnection(Settings.Default.StateAnalysisConnection))
        {
            using (var cmd = conn.CreateCommand())
            {
                 cmd.CommandText = "Select Division From Divisions "
                    + "Where Region = '" + region + "'";
                 conn.Open();
                 using (var reader = cmd.ExecuteReader())
                 {
                     while (reader.Read())
                     {
                         results.Add((string)reader["Division"]);
                     }
                 }
             }
         }

         return results;
     }
     catch (Exception ex)
     {
         throw new Exception("Database error in StateRepository", ex);
     }
     finally
     {
         if (connection.State == ConnectionState.Open)
             connection.Close();
     }
}

Answer 1

在“ Regions列表框的SelectedIndexChanged事件中，獲取所選區域，然后在GetDivisionsInRegion方法中使用該區域，並在結果中填充“ Divisions列表框。

private void Regions_SelectedIndexChanged(object sender, System.EventArgs e)
{
   // Get the currently selected item in the ListBox. 
   string region = Regions.SelectedItem.ToString();

   // Find the divisions in the region
   IEnumerable<string> divisions = GetDivisionsInRegion(region);

   //set as this as the new data source for your Divisions listbox
   Divisions.DataSource = divisions;
}

盡管我認為您可能必須將除法轉換為List<string>或獲取GetDivisionsInRegion以返回List<string> 。