如果我选择一个组合框国家不改变另一个组合框中的状态..请帮助我

问题描述

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;
using System.Data.SqlClient;

namespace country_state_city
{
    public partial class Form1 : Form
    {

        SqlConnection con = new SqlConnection(*************);
        
        public Form1()
        {
            InitializeComponent();
           
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            
            SqlCommand cmd = new SqlCommand("select * from Country", con);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds);
            comboBox1.SelectedIndex = -1;
            comboBox1.DataSource = ds.Tables[0];
           
            comboBox1.DisplayMember = "County";
            comboBox1.ValueMember = "Countryid";
           
            
        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            //MessageBox.Show(comboBox1.SelectedIndex.ToString());
            if (comboBox1.SelectedIndex >= 0)
            {

                SqlDataAdapter da = new SqlDataAdapter("Select * From CountryState Where CountryId='" + comboBox1.SelectedValue + "'", con);
                DataSet ds = new DataSet();
                da.Fill(ds);

                comboBox2.DataSource = ds.Tables[0];
                comboBox2.DisplayMember = "State";
                comboBox2.ValueMember = "StateId";
            }
            
        }

        

        private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (comboBox2.SelectedIndex > 0)
            {

                SqlDataAdapter da = new SqlDataAdapter("Select * From StateCity Where StateId='" + comboBox2.SelectedValue + "'", con);
                DataSet ds = new DataSet();
                da.Fill(ds);

                comboBox3.DataSource = ds.Tables[0];
                comboBox3.DisplayMember = "City";
                comboBox3.ValueMember = "CityId";
            }
        }
    }
}

推荐答案

this.comboBox1.SelectedIndexChanged -= new System.EventHandler(this.comboBox1_SelectedIndexChanged);
SqlCommand cmd = new SqlCommand("select * from Country", con);
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();

然后在填充comboBox之后，可以订阅该事件，并强制进行选择，例如

Then after you have populated the comboBox, you can subscribe to the event, and force a selection to happen e.g.

comboBox1.SelectedIndex = -1;
this.comboBox1.SelectedIndexChanged += new System.EventHandler(this.comboBox1_SelectedIndexChanged);
comboBox1.SelectedIndex = 0;

2.您的comboBox1将填充数字，因为您使用了

2. Your comboBox1 is going to populated with numbers because you have used

comboBox1.DisplayMember = "County";

- 没有这样的列，它应该是计数 r y



3.永远不要使用字符串连接来构建像这样的SQL语句

- there is no such column, it should be Country

3. Never use string concatenation to build your sql statements like this

SqlDataAdapter da = new SqlDataAdapter("Select * From CountryState Where CountryId='" + comboBox1.SelectedValue + "'", con);

你对自己敞开大门 [] - 使用参数化查询，例如

You leave yourself wide open to SQL Injection attacks[^] - use parameterized queries instead e.g.

SqlCommand cmd = new SqlCommand("Select * from StateCity Where StateId=@id", con);
cmd.Parameters.AddWithValue("@id", comboBox2.SelectedValue);
SqlDataAdapter da = new SqlDataAdapter(cmd);

4.您需要养成使用一些最佳实践的习惯，例如 []和 []

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;
using System.Data.SqlClient;
namespace country_state_city
{
    public partial class Form1 : Form
    {
        SqlConnection con = new SqlConnection("*************");
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            SqlCommand cmd = new SqlCommand("select * from Country", con);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds);

            comboBox1.DataSource = ds.Tables[0];

            comboBox1.DisplayMember = "County";
            comboBox1.ValueMember = "Countryid";
            comboBox1.SelectedIndex = 0;
        }
        private void button1_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            MessageBox.Show(comboBox1.SelectedIndex.ToString());
            if (comboBox1.SelectedIndex >= 0)
            {
                SqlDataAdapter da = new SqlDataAdapter("Select * From CountryState Where CountryId='" + comboBox1.SelectedValue + "'", con);
                DataSet ds = new DataSet();
                da.Fill(ds);

                comboBox2.DataSource = ds.Tables[0];
                comboBox2.DisplayMember = "State";
                comboBox2.ValueMember = "StateId";
                comboBox2.SelectedIndex = 0;
            }
        }
        private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (comboBox2.SelectedIndex >= 0)
            {
                SqlDataAdapter da = new SqlDataAdapter("Select * From StateCity Where StateId='" + comboBox2.SelectedValue + "'", con);
                DataSet ds = new DataSet();
                da.Fill(ds);
                comboBox3.DataSource = ds.Tables[0];
                comboBox3.DisplayMember = "City";
                comboBox3.ValueMember = "CityId";
                comboBox3.SelectedIndex = 0;
            }
        }
    }
}

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