winform button 选择文件 OpenFileDialog

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string filetxt = textBox1.Text;
            if (!File.Exists(filetxt))
            {
                MessageBox.Show("您要查找的文件不存在");
                richTextBox1.Text = string.Empty;
                return;
            }
            else
            {
                string result = string.Empty;
                //文件实例化streamreader对象
                StreamReader sr = new StreamReader(filetxt, Encoding.GetEncoding("gb2312"));
                //调用readertoend 方法读取选中文件的全部内容
                result = sr.ReadToEnd();
                richTextBox1.Text = result;
                //关闭当前文件读取流
                sr.Close();
                return ;
            }

        }

        private void button2_Click(object sender, EventArgs e)
        {
            if (richTextBox1.Text != "" && richTextBox1.Text != string.Empty)
            {               
                string[] arry = richTextBox1.Text.Split('.');
                richTextBox1.Text = string.Empty;
                for (int i = 0; i <= arry.Length-1; i++)
                {
                    richTextBox1.Text += arry[i];
                }
            }
            else
            {
                MessageBox.Show("您要截取的数据不存在");
                richTextBox1.Text = string.Empty;
                return;
            }
        }

        private void button3_Click(object sender, EventArgs e)
        {
           
            //初始化一个OpenFileDialog类
            OpenFileDialog fileDialog = new OpenFileDialog();
           

            //判断用户是否正确的选择了文件
            if (fileDialog.ShowDialog() == DialogResult.OK)
            {

　　　　　　//文件名
                textBox1.Text = fileDialog.FileName;
                string filetxt = textBox1.Text;
                if (!File.Exists(filetxt))
                {
                    MessageBox.Show("您要查找的文件不存在");
                    richTextBox1.Text = string.Empty;
                    return;
                }
                else
                {
                    string result = string.Empty;
                    //文件实例化streamreader对象
                    StreamReader sr = new StreamReader(filetxt, Encoding.GetEncoding("gb2312"));
                    //调用readertoend 方法读取选中文件的全部内容
                    result = sr.ReadToEnd();
                    richTextBox1.Text = result;
                    //关闭当前文件读取流
                    sr.Close();
                    return;
                }
            //获取用户选择文件的后缀名
            //string extension = Path.GetExtension(fileDialog.FileName);
            //声明允许的后缀名
            //string[] str = new string[] { ".gif", ".jpge", ".jpg" };
            //if (!str.Contains(extension))
            //{
            //MessageBox.Show("仅能上传gif,jpge,jpg格式的图片！");
            //}
            //else
            //{
            ////获取用户选择的文件，并判断文件大小不能超过20K，fileInfo.Length是以字节为单位的
            //FileInfo fileInfo = new FileInfo(fileDialog.FileName);
            //if (fileInfo.Length  > 20480)
            //{
            //MessageBox.Show("上传的图片不能大于20K");
            //}
            //else
            //{
            ////在这里就可以写获取到正确文件后的代码了
            //}
            }
    //        }
        }
    }
}