组合框数据绑定（C＃winforms）

Question

where is the problem with this code? When i start the program there is no values to choose from comboBox. There is no problems with compiling and starting an application. I have no idea what is wrong here. Maybe someone have solution for this problem.

Link to 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

我认为您只定义了LoadCustomersId（）方法，但您没有从任何地方调用它。您需要调用该方法

Answer 2

Add this to your code.

The reason behind this is that when you launch your application, nothing is calling LoadCustomersId() function to populate the data on your comboBox. So use the Load event handler and populate your combobox from there:

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