iOS: Using persistant storage

iOS: Using persistant storage

• 1.
  iOS:  Persistant  Storage   Jussi  Pohjolainen  
• 2.
  Overview   •  iOS  provides  many  ways  of  saving  and  loading  data     •  NSUserDefaults   –  Simple  mechanism  for  preferences   •  Archiving   –  Save  and  load  data  model  object  a<ributes  from  file   system   •  Wri;ng  to  File  System   –  Easy  mechanism  for  reading  and  wri@ng  bytes   •  SQLite   –  Rela@onal  database  
• 3.
  NSUserDefaults   •  Default  database  is  created  automa@cally  for   each  user   •  Saves  and  loads  data  to  database   •  At  run@me  caches  informa@on  to  avoid  having  to   open  connec@on  to  the  database   –  synchronize  method  will  save  cache  to  database   –  synchronize  method  is  invoked  at  periodic  intervals   •  Methods  for  saving  and  loading  NSData,   NSString,  NSNumber,  NSDate,  NSArray  and   NSDic@onary   –  Any  other  object;  archive  it  to  NSData  
• 4.
  Example  NSUserDefaults:  Saving   NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; [defaults setObject:firstName forKey:@"firstName"]; [defaults setObject:lastName forKey:@"lastname"]; [defaults synchronize];
• 5.
  Example  NSUserDefaults:  Loading   NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; NSString *firstName = [defaults objectForKey:@"firstName"]; NSString *lastName = [defaults objectForKey:@"lastname"];
• 6.
  Archiving   •  NSUserDefaults  is  good  for  storing  simple  data   •  If  the  applica@on  model  is  complex,  archiving   is  a  good  solu@on   •  Archiving?   –  Saving  objects  (=instance  variables)  to  file  system   •  Classes  that  are  archived  must   –  Conform  NSCoding  protocol   –  Implement  two  methods:  encodeWithCoder  and   initWithCoder  
• 7.
  Example   @interface Person: NSObject <NSCoding> { NSString* name; int id; } - (void) encodeWithCoder:(NSCoder* ) aCoder; - (void) initWithCoder:(NSCoder* ) aDeCoder; * * * - (void) encodeWithCoder:(NSCoder* ) aCoder { [aCoder encodeObject: name forKey:@"personName"]; [aCoder encodeInt: id forKey:@"personId"]; } - (void) initWithCoder:(NSCoder* ) aDeCoder { self = [super init]; if(self) { name = [aDecoder decodeObjectForKey:@"personName"]; id = [aDecoder decodeIntForKey:@"personId"]; } return self; }
• 8.
  About  Applica@on  Sandbox   •  Every  iOS  app  has  its  own  applica@on  sandbox   •  Sandbox  is  a  directory  on  the  filesystem  that  is  barricaded   from  the  rest  of  the  file  system   •  Sandbox  directory  structure   –  Library/Preferences   •  Preferences  files.  Backed  up.   –  Tmp/   •  Temp  data  storage  on  run@me.  NSTemporaryDirectory  will  give  you  a   path  to  this  dir   –  Documents/   •  Write  data  for  permanent  storage.  Backed  up.   –  Library/Caches   •  Same  than  Documents  except  it’s  not  backed  up.  Example:  fetch  large   data  from  web  server  and  store  it  here.  
• 9.
  Archiving  to  Documents/  dir   // Searches file system for a path that meets the criteria given by the // arguments. On iOS the last two arguments are always the same! (Mac OS X has several // more options) // // Returns array of strings, in iOS only one string in the array. NSArray *documentDirectories = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserFomainMask, YES); // Fetch the only document directory found in the array NSString *documentDirectory = [documentDirectories objectAtIndex:0]; // Add file name to the end of the array NSString *path = [documentDirectory stringByAppendingPathComponent:@"file.archive"];
• 10.
  NSKeyedArchiver  and   NSKeyedUnarchiver   •  NSKeyedArchiver  provides  a  way  to  encode   objects  into  a  file.   [NSKeyedArchiver archiveRootObject: someObject toFile: path]; •  NSKeyedUnarchiver  decodes  the  objects  from   file   someObject = [NSKeyedUnArchiver unarchiveObjectWithFile: path];
• 11.
  Reading  and  Wri@ng  Files   •  NSData  and  NSString  provides  easy  access  for   reading  and  wri@ng  bytes.     •  NSDic@onary  has  also  methods  for  saving  and   storing  the  dic@onary  to  property  list  (xml  file)   •  Also  standard  file  I/O  func@ons  from  C  library   available   –  fopen,  fread,  fwrite    
• 12.
  Wri@ng  to  File  System  using  NSData   •  NSData  provides  convinient  methods  for   reading  and  wri@ng  to  file  system   –  - writeToFile:atomically –  + dataWithContentsOfFile •  Example   –  [someData writeToFile:path atomically:YES] –  NSData* data = [NSData dataWithContestOfFile: path];