窗體拖拽一個button，代碼樣例中使用OpenFileDialog對象new一個新實例，等同于在窗體拖拽OpenFileDialog控件，兩種方式都可以，實現功能效果是相同的

using System;
using System.Windows.Forms;

namespace WindowsFormsApp11
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string path = "";
            OpenFileDialog openFileDialog1 = new OpenFileDialog();
            // 打開目錄定位到當前應用程序目錄
            openFileDialog1.InitialDirectory = Application.StartupPath;
            // 設置OpenFileDialog組件的Filter過濾出多種擴展名的文件
            openFileDialog1.Filter = "All files (*.*)|*.*|text files (*.txt;)|*.txt;";
            //openFileDialog1.Filter = "Image Files(*.BMP;*.JPG;*.GIF)|*.BMP;*.JPG;*.GIF|All files(*.*)|*.*";
            // 設置默認文件類型顯示順序
            openFileDialog1.FilterIndex = 2;
            // 是否記憶上次打開的目錄  
            openFileDialog1.RestoreDirectory = true;
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                // 獲取文件路徑
                path = openFileDialog1.FileName;
                MessageBox.Show(path);
                // 業務操作...
                // 業務操作...
                // 業務操作...
            }
        }
    }
}