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;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            pictureBox1.Image = Image.FromFile("u=511638845,3861741470&fm=0&gp=0[1].jpg");

            toolTip1.SetToolTip(pictureBox1, "自然风光");

        }

        private void pictureBox1_Click(object sender, EventArgs e)
        {

        }

        private void toolTip1_Popup(object sender, PopupEventArgs e)
        {

        }
    }
}

注意：因为要用到文件的读写，所以在开头，要用到using System.IO;

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;

using System.IO;
using System.Windows.Forms;

namespace WindowsFormsApplication5
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void saveFileDialog1_FileOk(object sender, CancelEventArgs e)
        {


        }

        private void openFileDialog1_FileOk(object sender, CancelEventArgs e)
        {
       

        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.saveFileDialog1.Filter = "*.txt|*.txt";
            this.saveFileDialog1.ShowDialog();
            string file = this.saveFileDialog1.FileName;
            if (string.IsNullOrEmpty(file)) return;
            //以下为写字符到文本文件，需要添加System.IO引用
            //创建一个文件流
            FileStream fs = new FileStream(file, FileMode.OpenOrCreate,
                FileAccess.Write);
            //创建一个StreamWriter对象
            StreamWriter sw = new StreamWriter(fs);
            sw.Write(this.textBox1.Text);
            //释放StreamWriter对象,文件流对象
            sw.Dispose();
            fs.Dispose();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            this.openFileDialog1.Filter = "*.txt|*.txt";
            this.openFileDialog1.ShowDialog();
            string file = this.openFileDialog1.FileName;
            if (string.IsNullOrEmpty(file)) return;

            //以下为写字符到文本文件，需要添加System.IO引用
            //创建一个文件流
            FileStream fs = new FileStream(file, FileMode.Open,
                FileAccess.Read);
            //创建一个StreamWriter对象
            StreamReader sr = new StreamReader(fs);
            this.textBox1.Text = sr.ReadToEnd();
            //释放StreamWriter对象,文件流对象
            sr.Dispose();
            fs.Dispose();
        }
    }
}