C#.09 PictureBox图片控件

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 _1.Properties;

namespace _1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        string imagename="1";
        private void timer1_Tick(object sender, EventArgs e)
        {
            if (imagename == "1")
            {
                imagename = "2";
                pictureBox1.Image =Resources._2;
            }
            else if (imagename == "2")
            {
                imagename = "3";
                pictureBox1.Image = Resources._3;
            }
            else if (imagename == "3")
            {
                imagename = "4";
                pictureBox1.Image = Resources._4;
            }
            else if (imagename == "4")
            {
                imagename = "5";
                pictureBox1.Image = Resources._5;
            }
            else if (imagename == "5")
            {
                imagename = "1";
                pictureBox1.Image = Resources._1;
            }
        }
        private void button1_Click(object sender, EventArgs e)
        {
            timer1.Interval=150;
            timer1.Start();
        }
    }
}