根据第一个 ComboBox (1) c# 的输入，从 ComboBox (2) 中消除一个选项

Question

我正在创建一个航空公司预订系统，我有 2 个组合框。第一个是出发城市，第二个是到达城市。我希望能够从第二个组合框中消除第一个组合框中的选择，因为我不希望同一个城市能够同时作为出发城市和到达城市提交。我正在从数据库中查询城市名称。

这是我的代码：

public partial class main : Form
{
    public main()
    {
        InitializeComponent();

        string connectionString = @"Base Schema Name=cyanair;data source=C:\Users\Client 0819\source\repos\Cyanair\cyanair.db";

        //Departure ComboBox
        SQLiteConnection conn = new SQLiteConnection(connectionString);
        try
        {
            conn.Open();
            SQLiteCommand cmd = new SQLiteCommand();

            cmd.Connection = conn;
            cmd.CommandType = System.Data.CommandType.Text;
            cmd.CommandText = "SELECT * FROM CyanairAirports";

            SQLiteDataAdapter da = new SQLiteDataAdapter(cmd);

            DataTable dt = new DataTable();
            da.Fill(dt);
            comboDeparture.DataSource = dt;
            comboDeparture.ValueMember = "Descriptions";
            comboDeparture.DisplayMember = "Descriptions";



            conn.Close(); 
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

    //Arrival ComboBox
    private void comboDeparture_DisplayMemberChanged(object sender, EventArgs e)
    {
        string connectionString = @"Base Schema Name=cyanair;data source=C:\Users\Client 0819\source\repos\Cyanair\cyanair.db";
        SQLiteConnection conn = new SQLiteConnection(connectionString);

        **String city = comboDeparture.DisplayMember;**

        try
        {
            conn.Open();
            SQLiteCommand cmd = new SQLiteCommand();


            cmd.Connection = conn;
            cmd.CommandType = System.Data.CommandType.Text;
            cmd.CommandText = "SELECT * FROM CyanairAirports WHERE Descriptions IS NOT '" + comboDeparture.SelectedValue.ToString() + "'";
            richTextBox1.Text = "SELECT * FROM CyanairAirports WHERE Descriptions IS NOT '" + comboDeparture.SelectedValue + "'";
            SQLiteDataAdapter da = new SQLiteDataAdapter(cmd);

            DataTable dt = new DataTable();
            da.Fill(dt);
            comboArrival.DataSource = dt;
            comboArrival.ValueMember = "Descriptions";
            comboArrival.DisplayMember = "Descriptions";


            conn.Close();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
        }

谢谢:)

Answer 1

您似乎正在处理comboDeparture 上的DisplayMemberChanged 事件，并尝试在该处理程序中更新comboArrival 的值。但是，DisplayMemberChanged 仅在 DisplayMember 属性更改时触发。

DisplayMember 只告诉控件在数据绑定控件上显示哪个属性。它与ComboBox 中选择的索引或值无关。因此，填充comboArrival 的代码只有在您设置comboDepartarture.DisplayMember 时在构造函数中运行。相反，处理ComboBox.SelectedIndexChanged 或ComboBox.SelectedValueChanged 并设置comboArrival 的项目。

关于您的代码需要注意的其他一些重要事项。

首先，您应该在运行 Sql 语句时使用参数化查询，而不是连接字符串。在你做的时候连接字符串打开你到SQL Injection Attacks。我对 SqlLite 不熟悉，无法为您提供如何修改代码的示例，但也许 this question 可以提供帮助。

其次，您不必每次更改comboDeparture 中的选定值时都重新运行查询。只需在Form 上添加comboArrival 的数据源作为字段，即可对其进行过滤。比如……

public partial class main : Form
{
   // Your constructors...

   private void comboDepartures_SelectedIndexChanged(object sender, EventArgs e)
   {
      if (_arrivalsDataSource == null)
      {
          _arrivalsDataSource = new System.Data.DataTable();
          // Load _arrivalsDataSource from the database, basically how you're doing it now.
          comboArrival.DataSource = _arrivalsDataSource.DefaultView;
          comboArrival.DisplayMember = "Descriptions"
          comboArribal.ValueMember = "Descriptions"
      }
      if (comboDeparture.SelectedIndex == -1)
      {
          _arrivalsDataSource.DefaultView.RowFilter = null; // Clear the filter.
      }
      else
      {
          // Set the filter.
          _arrivalsDataSource.DefaultView.RowFilter = $"Description <> '{comboDeparture.SelectedValue}'";
      }
   }

   private System.Data.DataTable _arrivalsDataSource = null;
}