如何在本地缓存上关闭并存储文本文件

I am developing an IOS app..Download data From URL and save on local cache..but i am using this code..first time data can stored in Local cache and also read on the text field..but Delete the app on simulator and run the and again store the text file on local cache..file can't be store..Any help or advice is greatly appreciated. thanks in advance.I am developing an IOS app..Download data From