private void button1_Click(object sender, System.EventArgs e)
{
FileStream fs;

if(openFileDialog1.ShowDialog()==DialogResult.OK)
{
textBox2.Text = openFileDialog1.FileName;
try
{
fs = File.OpenRead(textBox2.Text);
byte[] arr = new byte[fs.Length];
UTF8Encoding data =new UTF8Encoding(true);
while(fs.Read(arr,0,arr.Length)>0)
{
textBox1.Text = data.GetString(arr);
}
}
catch
{
MessageBox.Show("读取文件时出错","错误",System.Windows.Forms.MessageBoxButtons.OK,System.Windows.Forms.MessageBoxIcon.Warning);
return;
}

}
}

[此贴子已经被作者于2006-9-7 14:29:48编辑过]

完整的代码，帮忙看看
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.IO;
using System.Text;

namespace WindowsApplication1
{
public class Form1 : System.Windows.Forms.Form
{
private System.Windows.Forms.Label label1;
private System.Windows.Forms.TextBox textBox1;
private System.Windows.Forms.Button button1;
private System.Windows.Forms.TextBox textBox2;
private System.Windows.Forms.Button button2;

private System.ComponentModel.Container components = null;

public Form1()
{
InitializeComponent();
}

protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

private void InitializeComponent()
{
this.label1 = new System.Windows.Forms.Label();
this.textBox1 = new System.Windows.Forms.TextBox();
this.button1 = new System.Windows.Forms.Button();
this.textBox2 = new System.Windows.Forms.TextBox();
this.button2 = new System.Windows.Forms.Button();
this.SuspendLayout();

this.label1.Location = new System.Drawing.Point(16, 16);
this.label1.Name = "label1";
this.label1.Size = new System.Drawing.Size(56, 16);
this.label1.TabIndex = 0;
this.label1.Text = "文件名称";

this.textBox1.Location = new System.Drawing.Point(96, 8);
this.textBox1.Name = "textBox1";
this.textBox1.Size = new System.Drawing.Size(176, 21);
this.textBox1.TabIndex = 1;
this.textBox1.Text = "";

this.button1.Location = new System.Drawing.Point(304, 8);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(72, 24);
this.button1.TabIndex = 2;
this.button1.Text = "浏览";
this.button1.Click += new System.EventHandler(this.button1_Click);

this.textBox2.Location = new System.Drawing.Point(24, 48);
this.textBox2.Multiline = true;
this.textBox2.Name = "textBox2";
this.textBox2.Size = new System.Drawing.Size(432, 184);
this.textBox2.TabIndex = 3;
this.textBox2.Text = "";

this.button2.Location = new System.Drawing.Point(392, 8);
this.button2.Name = "button2";
this.button2.Size = new System.Drawing.Size(72, 24);
this.button2.TabIndex = 4;
this.button2.Text = "修改";

this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
this.ClientSize = new System.Drawing.Size(472, 261);
this.Controls.Add(this.button2);
this.Controls.Add(this.textBox2);
this.Controls.Add(this.button1);
this.Controls.Add(this.textBox1);
this.Controls.Add(this.label1);
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false);

}

[STAThread]
static void Main()
{
Application.Run(new Form1());
}

private void button1_Click(object sender, System.EventArgs e)
{
OpenFileDialog open = new OpenFileDialog();
/*if(open.ShowDialog()==DialogResult.OK)
{
textBox1.Text = open.FileName;
FileStream fs = null;
try
{
fs = File.OpenRead(textBox1.Text);
byte[] content = new byte[fs.Length];
UTF8Encoding data = new UTF8Encoding(true);
while(fs.Read(content,0,content.Length)>0)
{
textBox2.Text += data.GetString(content);
}
}
catch
{
MessageBox.Show("读取文件出错","错误");
return;
}
finally
{
fs.Close();
}
}*/

if(open.ShowDialog()==DialogResult.OK)
{
textBox1.Text = open.FileName;
StreamReader sr = null;
try
{
sr = File.OpenText(textBox1.Text);
String s = null;
while((s=sr.ReadLine())!=null)
{
textBox2.Text += s;
}
}
catch
{
MessageBox.Show("读取文件出错","错误");
return;
}
finally
{
sr.Close();
}
}
}
}
}