车牌号查询 （FolderBrowserDialog读取）

1、这是第一个版本，文件路径需要用户输入，下个版本打开即加载

2、重点学习FolderBrowserDialog控件

3、注意内容在再次打开之前，清除上次的数据内容，使用using和函数代替字符串，都是为了数据的安全性考虑

代码如下：

namespace 车牌查询
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load_1(object sender, EventArgs e)
        {
            cbxSheng.Items.Add("安徽省"); //这里知道文件里面只有三个省，提前添加
            cbxSheng.Items.Add("江苏省");
            cbxSheng.Items.Add("浙江省");

        }

        private void btnData_Click_1(object sender, EventArgs e)
        {
            FolderBrowserDialog fbd = new FolderBrowserDialog(); //打开寻找路的程序
            if (fbd.ShowDialog() != DialogResult.OK)
            {
                return;//如果取消就终止程序，如果没有这步，程序后面获取不到路径，发生错误
            }
            string filePath = fbd.SelectedPath;//获取用户获取的文件夹路径

            string[] files = Directory.GetFiles(filePath, "*.txt", SearchOption.AllDirectories);//将找到的".txt"格式的文件储存到前面files数组中

            foreach (string file in files)//增强for循环，一边遍历数据，一边储存数据
            {
                string sheng = Path.GetFileNameWithoutExtension(file);//以每个文件的名字，存到"省"中

                string[] lines = File.ReadAllLines(file, Encoding.Default);//逐行读取数据
                foreach (string line in lines)
                {
                    string[] str = line.Split(' ');//以' '为分隔符
                    string shi = str[0];//索引
                    string chepai = str[1];

                    using (SqlConnection conn = new SqlConnection("Data Source=DESKTOP-BEUJ3C4;Initial Catalog=DBCarId;User ID=sa;Password =2323010676;"))
                    {
                        conn.Open();
                        SqlCommand cmd = conn.CreateCommand();
                        cmd.CommandText = "insert into Table_CarId(省,市,车牌) values(@sheng,@shi,@chepai)";
                        cmd.Parameters.Add(new SqlParameter("sheng", sheng));
                        cmd.Parameters.Add(new SqlParameter("shi", shi));
                        cmd.Parameters.Add(new SqlParameter("chepai", chepai));
                        cmd.ExecuteNonQuery();

                    }
                }
            }
            MessageBox.Show("数据加载成功！");
        }

        private void btnClear_Click(object sender, EventArgs e)
        {
            using (SqlConnection conn = new SqlConnection("Data Source=DESKTOP-BEUJ3C4;Initial Catalog=DBCarId;User ID=sa;Password =2323010676;"))
            {
                conn.Open();
                SqlCommand cmd = conn.CreateCommand();
                cmd.CommandText = "delete from Table_CarId";
                cmd.ExecuteNonQuery();
                MessageBox.Show("清除成功！");

            }
        }

        
        private void cbxSheng_SelectedIndexChanged_1(object sender, EventArgs e)
        {
            cbxShi.Items.Clear();
            cbxShi.Text = "";
            txtChepai.Text = "";

            using (SqlConnection conn = new SqlConnection ("Data Source=DESKTOP-BEUJ3C4;Initial Catalog=DBCarId;User ID=sa;Password =2323010676;"))
            {
                conn.Open();
                SqlCommand cmd = conn.CreateCommand();
                cmd.CommandText = "select * from Table_CarId where 省=@sheng";
                cmd.Parameters.Add(new SqlParameter("sheng", cbxSheng.Text));
                SqlDataReader reader = cmd.ExecuteReader();
                while (reader.Read())
                {
                    cbxShi.Items.Add(reader.GetString(reader.GetOrdinal("市")));
                }
            }    
        }

        private void btnSelect_Click_1(object sender, EventArgs e)
        {
            using (SqlConnection conn = new SqlConnection("Data Source=DESKTOP-BEUJ3C4;Initial Catalog=DBCarId;User ID=sa;Password =2323010676;"))
            {
                conn.Open();
                SqlCommand cmd = conn.CreateCommand();
                cmd.CommandText = "select * from Table_CarId where 市=@shi";
                cmd.Parameters.Add(new SqlParameter("shi", cbxShi.Text));
                SqlDataReader reader = cmd.ExecuteReader();
                if (reader.Read())
                {
                    txtChepai.Text = reader.GetString(reader.GetOrdinal("车牌"));
                }
            }   
        }

    }
}