C#访问网络图片，先从本地获取，如果没有再从网络获取，保存到本地

using ScreenShowManage.Entity;
using System;
using System.Collections.Generic;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading.Tasks;

namespace ScreenShowManage
{
    public static class EmployeePhotoUtil
    {
        /// <summary>
        /// 获取照片
        /// </summary>
        /// <param name="photoUrl">照片地址</param>
        /// <param name="name">照片名称</param>
        /// <returns></returns>
        public static Image GetEmployeePhoto(string photoUrl, string name)
        {
            Image image = null;
            if (string.IsNullOrEmpty(photoUrl))
            {
                return null;
            }
            try
            {
                image = GetEmpPhotoPic(name);
                if (image != null)
                    return image;

                WebRequest webreq = WebRequest.Create(photoUrl);
                // 设置web访问照片超时时间
                webreq.Timeout = 200;
                WebResponse webres = webreq.GetResponse();
                Stream stream = webres.GetResponseStream();
                image = Image.FromStream(stream);
                if (image != null)
                    image.Save(GetEmpPhotoCachePath() + "/" + name);
                stream.Close();
            }
            catch (WebException ex)
            {
                image = null;
            }
            //if (image == null)
            //{
            //    string path = GetEmpPhotoCachePath() + "unKnown.jpg";
            //    Image myImage = Image.FromFile(path);
            //    return myImage;
            //}
            //else
            return image;
        }

        /// <summary>
        /// 获取本地照片
        /// </summary>
        /// <param name="name"></param>
        /// <returns></returns>
        private static Image GetEmpPhotoPic(string name)
        {
            try
            {
                string path = GetEmpPhotoCachePath() + name;
                Image myImage = Image.FromFile(path);
                return myImage;
            }
            catch (Exception ex)
            {
                return null;

            }
        }

        /// <summary>
        /// 获取本地缓存职工照片目录
        /// </summary>
        /// <returns></returns>
        private static string GetEmpPhotoCachePath()
        {
            try
            {
                string strName = "EmpPhoto";
                if (!Directory.Exists(strName))
                {
                    Directory.CreateDirectory(strName);
                }
                return strName + "/";
            }
            catch (Exception ex)
            {
                return "";
            }
        }
    }
}