1、获取Documents路径，2条代码：
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = paths[0];
2、获取Library路径，2条代码：
NSArray paths = NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES);
NSString *libraryDirectory = paths[0];
3、获取tmp路径，1条代码：
NSString *tempPath = NSTemporaryDirectory();
