C#winform省市县联动，以及有的县是空值时显示异常的处理

一、如下comboBox1、comboBox2、comboBox3，原来这三个都是空的，

将数据库中的省份传递到comboBox1中

我的数据库有parent字段，根据市的parent找到省，根据县的找到市，所以下面的sql语句在省市县联动时，sql语句是一样的

二、代码

1、在Load方法中，加载省份(根据需求变换sql语句)

 private void Form1_Load(object sender, EventArgs e)
        {
           
            using (SQLiteConnection con = new SQLiteConnection(Constants.DATA_SOURCE))
            {
                con.Open();
                using (SQLiteCommand cmd = new SQLiteCommand())
                {
                    cmd.Connection = con;
                    cmd.CommandText = string.Format("select * from test t where t.[district_level]=2");
                    int rows = cmd.ExecuteNonQuery();
                    SQLiteDataAdapter sda = new SQLiteDataAdapter(cmd);
                    DataTable dt = new DataTable();
                    sda.Fill(dt);
                    comboBox1.DataSource = dt;
                    comboBox1.DisplayMember = "name";
                    comboBox1.ValueMember="id";
                }
            }
         

        }

(1)、用sql命令查询要在comboBox中显示的值

(2)、将值给DataTable

(3)、DisplayMember 就是要显示的数据库中的字段：name

(4)、ValueMember：一般是数据库中的主键：id

2、进入comboBox1事件，根据省份，显示市

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
          
            if (comboBox1.SelectedIndex > -1)
            {
                DataRowView drv = (DataRowView)comboBox1.SelectedItem;
                string id = drv.Row["id"].ToString();//获得已绑定的选项的id

                using (SQLiteConnection con = new SQLiteConnection(Constants.DATA_SOURCE))
                {
                    con.Open();
                    using (SQLiteCommand cmd = new SQLiteCommand())
                    {
                        cmd.Connection = con;
                        cmd.CommandText = string.Format("select * from test t where t.[parent]='" + id + "'");
                        int rows = cmd.ExecuteNonQuery();
                        SQLiteDataAdapter sda = new SQLiteDataAdapter(cmd);
                        DataTable dt = new DataTable();
                        sda.Fill(dt);
                        comboBox2.DataSource = dt;
                        comboBox2.DisplayMember = "name";
                        comboBox2.ValueMember = "id";
                    }
                }
                
              }


        }

3、进入comboBox2事件，根据市，显示县

private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {
            
            if (comboBox2.SelectedIndex > -1)
            {
                DataRowView drv = (DataRowView)comboBox2.SelectedItem;
                string id = drv.Row["id"].ToString();//获得id

                using (SQLiteConnection con = new SQLiteConnection(Constants.DATA_SOURCE))
                {
                    con.Open();
                    using (SQLiteCommand cmd = new SQLiteCommand())
                    {
                        cmd.Connection = con;
                        cmd.CommandText = string.Format("select * from test t where t.[parent]='" + id + "'");
                        int rows = cmd.ExecuteNonQuery();
                        SQLiteDataAdapter sda = new SQLiteDataAdapter(cmd);
                        DataTable dt = new DataTable();
                        sda.Fill(dt);
                        comboBox3.DataSource = dt;
                        comboBox3.DisplayMember = "name";
                        comboBox3.ValueMember = "id";
                    }
                }

            }
            
        }

三、结果：

四、有的省没有县，县是空值时，联动会出现异常，上一次联动的县的值还在显示，

点击县时，因为县的下一级没有值，显示的还是上次联动的结果，其实它并没有处于选中状态，只是显示出来了

所以，处理一下，因为没有处于选中状态，所以SelectedIndex是-1

if(comboBox3.SelectedIndex!=0)
{
     comboBox3.Text = "";
}

五、其他：

1、如果一个页面有多条这样的省市县联动

把上面的步骤再来一遍即可,只是Load里需要注意，不能图省事把comboBox4直接加在comboBox1后，否则点下面的省份，上面的也会变

using (SQLiteConnection con = new SQLiteConnection(Constants.DATA_SOURCE))
            {
                con.Open();
                using (SQLiteCommand cmd = new SQLiteCommand())
                {
                    cmd.Connection = con;
                    cmd.CommandText = string.Format("select * from test where t.[district_level]=2");
                    int rows = cmd.ExecuteNonQuery();
                    SQLiteDataAdapter sda = new SQLiteDataAdapter(cmd);
                    DataTable dt = new DataTable();
                    sda.Fill(dt);
                    comboBox1.DataSource = dt;
                    comboBox1.DisplayMember = "name";
                    comboBox1.ValueMember="id";
                   
                }
            }


            using (SQLiteConnection con = new SQLiteConnection(Constants.DATA_SOURCE))
            {
                con.Open();
                using (SQLiteCommand cmd = new SQLiteCommand())
                {
                    cmd.Connection = con;
                    cmd.CommandText = string.Format("select * from test t where t.[district_level]=2");
                    int rows = cmd.ExecuteNonQuery();
                    SQLiteDataAdapter sda = new SQLiteDataAdapter(cmd);
                    DataTable dt = new DataTable();
                    sda.Fill(dt);
                  
                    comboBox4.DataSource = dt;
                    comboBox4.DisplayMember = "name";
                    comboBox4.ValueMember = "id";
                }
            }

2、把comboBox1的事件代码封装成一个类DBDao.cs，方法名为getAddress()

（1）sql语句用的一样的时候(上面说的，根据市的parent找到省，根据县的parent找到市)，我把sql语句也封装了

public static void getAddress(ComboBox combo1, ComboBox combo2)
        {
            if (combo1.SelectedIndex > -1)
            {
                DataRowView drv = (DataRowView)combo1.SelectedItem;
                string id = drv.Row["id"].ToString();//获得id
                using (SQLiteConnection con = new SQLiteConnection(Constants.DATA_SOURCE))
                {
                    con.Open();
                    using (SQLiteCommand cmd = new SQLiteCommand())
                    {
                        cmd.Connection = con;
                        cmd.CommandText = string.Format("select t.* from test t where t.[parent]='" + id + "'");
                        int rows = cmd.ExecuteNonQuery();
                        SQLiteDataAdapter sda = new SQLiteDataAdapter(cmd);
                        DataTable dt = new DataTable();
                        sda.Fill(dt);
                        combo2.DataSource = dt;
                        combo2.DisplayMember = "name";
                        combo2.ValueMember = "id";

                    }
                }
            }
        }

在comboBox1的点击事件中直接调用即可，

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            DBDao.getAddress(comboBox1, comboBox2);
        }

        private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {
            DBDao.getAddress(comboBox2, comboBox3);
        }

（2）sql语句不同的时候，不要把sql语句封装(留着以后用)

public static void ComboBoxLoad(string sql, ComboBox combobox)
        {
            using (SQLiteConnection con = new SQLiteConnection(Constants.DATA_SOURCE))
            {
                con.Open();
                using (SQLiteCommand cmd = new SQLiteCommand())
                {
                    cmd.Connection = con;
                    cmd.CommandText = string.Format(sql);
                    int rows = cmd.ExecuteNonQuery();
                    SQLiteDataAdapter sda = new SQLiteDataAdapter(cmd);
                    DataTable dt = new DataTable();
                    sda.Fill(dt);

                    combobox.DataSource = dt;
                    combobox.DisplayMember = "name";
                    combobox.ValueMember = "id";
                    
                }
            }


        }

其他页面调用：

string sql="select * from test t where t.id='0302' order by t.code asc";
DBDao.ComboBoxLoad(sql,comboBox12);

参考：

https://zhidao.baidu.com/question/242563101.html?qbl=relate_question_2&word=c%20combobox%BC%D3%D4%D8%CA%FD%BE%DD&skiptype=2