If, for example, you alternately read files from one directory and store them in another, each time the application offers you the last directory, it will be guaranteed to be wrong. The solution is to remember more than just one previous choice.

• 比如你交替地从一个目录中读文件，而在另一个目录保存文件。 程序每次提供给你的是上次的目录，那它肯定是错的，解决的方法就是记住多个过去选择。