C# 获取指定类型的所有文件

          public void GetAllFiles(DirectoryInfo dir, List<FileInfo> fileList,string extension=".png")
          {
              foreach (var item in dir.GetFiles())
              {
                  if (string.IsNullOrEmpty(extension) || item.Extension.Equals(extension))
                  {
                      fileList.Add(item);
                  }
              }
              foreach (var item in dir.GetDirectories())
              {
                  GetAllFiles(item, fileList,extension);
              }
          }