如何根据另一个列表框中的选定项目填充列表框？

Question

当我的表单加载区域列表框时，我有两个列表框（区域和分区）填充了4个区域（中西部，东北，南部，西部）。当我点击其中一个区域时，我希望Divisions列表框填充与点击区域相关的分区。我正在通过与我的SQL数据库进行通信的数据存储库。 在形式负载初始种群

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

背后的GetRegions方法代码：

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(); 
    } 
} 

是可以获得师在区域从所述分贝的方法：

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SelectedIndexChanged事件的你的Regions listbox，得到选定的区域，然后在你的GetDivisionsInRegion方法中使用它并填充Divisions列表框与结果。

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; 
} 

虽然我想你可能不得不铸师List<string>或让你的GetDivisionsInRegion返回一个List<string>。