将.txt文件组件附加到URL路径不起作用：
- var error:NSError?
- let manager = NSFileManager.defaultManager()
- let docURL = manager.URLForDirectory(.DocumentDirectory,inDomain:.UserDomainMask,appropriateForURL:nil,create:true,error:&error)
- docURL.URLByAppendingPathComponent("/RicFile.txt") <-- doesn't work
通过调试器：
- file:///Users/Ric/Library/Developer/CoreSimulator/Devices/
- <device id>/data/Containers/Data/Application/<app id>/Documents/
原因(通过错误)：
“The operation couldn’t be completed. Is a directory”
所以问题：为什么以下不起作用？
- docURL.URLByAppendingPathComponent("/RicFile.txt")
URLByAppendingPathComponent：不会改变现有的NSURL,它会创建一个新的NSURL.从
documentation：
URLByAppendingPathComponent: Returns a new URL made by appending a
path component to the original URL.
您需要将方法的返回值赋给某些东西.例如：
- let directoryURL = manager.URLForDirectory(.DocumentDirectory,error:&error)
- let docURL = directoryURL.URLByAppendingPathComponent("/RicFile.txt")
更好的方法是使用NSURL(string：String,relativeTo：NSURL)：
- let docURL = NSURL(string:"RicFile.txt",relativeTo:directoryURL)
