iOS: Using persistant storage
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The document discusses various methods for persistent storage in iOS, including NSUserDefaults for simple preferences, archiving objects to files by conforming to the NSCoding protocol, writing directly to files using NSData, and using SQLite for relational databases. NSUserDefaults provides a simple mechanism to save and load primitive data types. Archiving allows saving object graphs to files by implementing encode and decode methods. Files can also be read and written using NSData methods. The document also covers the application sandbox structure.
![Example
NSUserDefaults:
Saving
NSUserDefaults *defaults = [NSUserDefaults
standardUserDefaults];
[defaults setObject:firstName forKey:@"firstName"];
[defaults setObject:lastName forKey:@"lastname"];
[defaults synchronize];](https://image.slidesharecdn.com/persistant-storage-pptx-121119010221-phpapp01/85/iOS-Using-persistant-storage-4-320.jpg)
![Example
NSUserDefaults:
Loading
NSUserDefaults *defaults =
[NSUserDefaults standardUserDefaults];
NSString *firstName =
[defaults objectForKey:@"firstName"];
NSString *lastName =
[defaults objectForKey:@"lastname"];](https://image.slidesharecdn.com/persistant-storage-pptx-121119010221-phpapp01/85/iOS-Using-persistant-storage-5-320.jpg)
![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;
}](https://image.slidesharecdn.com/persistant-storage-pptx-121119010221-phpapp01/85/iOS-Using-persistant-storage-7-320.jpg)
![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"];](https://image.slidesharecdn.com/persistant-storage-pptx-121119010221-phpapp01/85/iOS-Using-persistant-storage-9-320.jpg)
![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];](https://image.slidesharecdn.com/persistant-storage-pptx-121119010221-phpapp01/85/iOS-Using-persistant-storage-10-320.jpg)
![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];](https://image.slidesharecdn.com/persistant-storage-pptx-121119010221-phpapp01/85/iOS-Using-persistant-storage-12-320.jpg)
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];