C# 拖放打开图片 并平铺窜窗口背景，选择一张图片拖动到窗口中（在本程序中其实不用拖动，只要选中图片超过2秒），就可以在窗口中显示该图片。在编写本程序的时候，不要忘了添加两个比较重要的名称空间：
using System.IO;//对文件进行操作
using System.Threading;//线程程序
同时本程序还自定义了图片和文件操作类：在窗体背景中显示被拖放的图片、向TreeView控件添加被拖放的文件夹目录，返回上一级目录、显示文件夹下所有子文件夹及文件的名称、获取文件夹中所有文件和文件夹、对单个FileSystemInfo进行判断,如果是文件夹则进行递归操作等，这些类可以用在其它的C#程序开发中。
SHOW FULL COLUMNS FROM `jrk_downrecords` [ RunTime:0.002770s ]
SELECT `a`.`aid`,`a`.`title`,`a`.`create_time`,`m`.`username` FROM `jrk_downrecords` `a` INNER JOIN `jrk_member` `m` ON `a`.`uid`=`m`.`id` WHERE `a`.`status` = 1 GROUP BY `a`.`aid` ORDER BY `a`.`create_time` DESC LIMIT 10 [ RunTime:0.168823s ]
SHOW FULL COLUMNS FROM `jrk_tagrecords` [ RunTime:0.002624s ]
SELECT * FROM `jrk_tagrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 20 [ RunTime:0.003102s ]
SHOW FULL COLUMNS FROM `jrk_member` [ RunTime:0.003253s ]
SELECT `id`,`username`,`userhead`,`usertime` FROM `jrk_member` WHERE `status` = 1 ORDER BY `usertime` DESC LIMIT 10 [ RunTime:0.005574s ]
SHOW FULL COLUMNS FROM `jrk_searchrecords` [ RunTime:0.002683s ]
SELECT * FROM `jrk_searchrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 5 [ RunTime:0.005316s ]
SELECT aid,title,count(aid) as c FROM `jrk_downrecords` GROUP BY `aid` ORDER BY `c` DESC LIMIT 10 [ RunTime:0.015499s ]
SHOW FULL COLUMNS FROM `jrk_articles` [ RunTime:0.002742s ]
UPDATE `jrk_articles` SET `hits` = 1 WHERE `id` = 74490 [ RunTime:0.001208s ]
