Question

这段代码的问题在哪里？当我启动程序时，没有值可以从comboBox中选择。编译和启动应用程序没有问题。我不知道这里有什么问题。也许有人有解决这个问题的方法。

链接到pastebin https://pastebin.com/pASVNWq

using MySql.Data.MySqlClient;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace parKing_new
{
    public partial class editClient : Form
    {
        public editClient()
        {
            InitializeComponent();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void button1_Click(object sender, EventArgs e)
        {}

    //Load customer ID to a combobox
        private void LoadCustomersId()
        {
            var connectionString = 
"Server=localhost;Port=3306;Database=ewisys;Uid=root;password=;";
            using (var connection = new MySqlConnection(connectionString))
            {
                connection.Open();
                var query = "SELECT clientID FROM clients";
                using (var command = new MySqlCommand(query, connection))
                {
                    using (var reader = command.ExecuteReader())
                    {
                        //Iterate through the rows and add it to the 
combobox's items
                        while (reader.Read())
                        {
                        comboBox1.Items.Add(reader.GetString("clientID"));
                        }
                    }
                }
            }
       }

        //Load customer details using the ID
        private void LoadCustomerDetailsById(int id)
        {
            var connectionString = 
"Server=localhost;Port=3306;Database=ewisys;Uid=root;password=;";
            using (var connection = new MySqlConnection(connectionString))
           {
               connection.Open();
               var query = "SELECT clientID, name, surName FROM clients WHERE 
Id = @clientID";
                using (var command = new MySqlCommand(query, connection))
                {
                //Always use SQL parameters to avoid SQL injection and it 
automatically escapes characters
                    command.Parameters.AddWithValue("@clientID", id);
                    using (var reader = command.ExecuteReader())
                    {
                        //No customer found by supplied ID
                        if (!reader.HasRows)
                            return;

                        ClientIDTextBox.Text = 
                    reader.GetInt32("clientID").ToString();
                    nameTextBox.Text = reader.GetString("name");
                    surNameTextBox.Text = reader.GetString("surName");
                    }
                }
           }
       }

      private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            var clientID = Convert.ToInt32(comboBox1.Text);
            LoadCustomerDetailsById(clientID);
        }
   }
}

Answer 1

我认为你只定义了LoadCustomersId（）方法，但是你没有从任何地方调用它。你需要调用方法

Answer 2

将此添加到您的代码中。

这背后的原因是当你启动应用程序时，没有任何东西调用LoadCustomersId（）函数来填充你的comboBox上的数据。因此，使用Load事件处理程序并从那里填充组合框：

private void editClient_Load(object sender, EventArgs e)
    {
       LoadCustomersId();
    }

组合框数据绑定（C＃winforms）

2 个答案: