How to retrieve data from NSUserDefaults? - ios

Question

currently, I try make an music playlist application. I try to save and retrieve playlist data from NSUserDefaults. I have no problem when saving the data but I got an error when retrieving data.
I got:
Terminating app due to uncaught exception 'MPMediaItemCollectionInitException', reason: '-init is not supported, use -initWithItems:
I'm following the answer from Play iPod playlist retrieved from a saved persistentid list but I try to write it in swift.
here is my save function:
func savePlaylist(var mediaItemCollection: MPMediaItemCollection){
var items: NSArray = mediaItemCollection.items
var listToSave: NSMutableArray = NSMutableArray()
for song in items{
var persistentId: AnyObject! = song.valueForProperty(MPMediaItemPropertyPersistentID)
listToSave.addObject(persistentId)
}
var data: NSData = NSKeyedArchiver.archivedDataWithRootObject(listToSave)
NSUserDefaults.standardUserDefaults().setObject(data, forKey: "songsList")
NSUserDefaults.standardUserDefaults().synchronize()
}
and here is my retrieve function:
func setupMusic(){
if NSUserDefaults.standardUserDefaults().objectForKey("songsList") != nil{
var theList: NSMutableArray = NSMutableArray()
var data: NSData = (NSUserDefaults.standardUserDefaults().objectForKey("songsList") as? NSData)!
var decodedData: NSArray = (NSKeyedUnarchiver.unarchiveObjectWithData(data) as? NSArray)!
theList.addObjectsFromArray(decodedData as [AnyObject])
var allTheSongs: NSMutableArray = NSMutableArray()
for var i = 0; i < theList.count; i++ {
var songQuery = MPMediaQuery.songsQuery()
var songs: NSArray = songQuery.items
allTheSongs.addObject(songs)
}
var currentQueue: MPMediaItemCollection = MPMediaItemCollection()
myMusicPlayer?.setQueueWithItemCollection(currentQueue)
}else{
println("fail!!!!!!!!!!!!")
}
}
How can I fix it?

Answer 1

Here is the issue var currentQueue: MPMediaItemCollection = MPMediaItemCollection()
You must init with items
As per the documentation by apple.
init(items:)
Designated Initializer
Initializes a media item collection with an array of media items.
Declaration
Swift
init!(items items: [AnyObject]!)
Parameters
items
The array of items you are assigning to the media item collection.
You have to init with items like
var currentQueue: MPMediaItemCollection = MPMediaItemCollection(items:itemsArray)

Answer 2

I am giving you a very simple way to any kind of object and retrieve from NSUserDefault .
You don't need to use explicitly archive and unarchive .
Just create a category of NSUserDefaults as follow
#import <Foundation/Foundation.h>
#interface NSUserDefaults (AKSNSUserDefaults)
- (void)saveCustomObject:(id<NSCoding>)object
key:(NSString *)key;
- (id<NSCoding>)loadCustomObjectWithKey:(NSString *)key;
#end
#implementation NSUserDefaults (AKSNSUserDefaults)
- (void)saveCustomObject:(id<NSCoding>)object
key:(NSString *)key {
NSData *encodedObject = [NSKeyedArchiver archivedDataWithRootObject:object];
[self setObject:encodedObject forKey:key];
[self synchronize];
}
- (id)loadCustomObjectWithKey:(NSString *)key {
NSData *encodedObject = [self objectForKey:key];
id object = [NSKeyedUnarchiver unarchiveObjectWithData:encodedObject];
return object;
}
#end
and than your NSUserDefaults is ready to store any object . but one thing is need to use NSCoder in your object model .
for example :
#import <Foundation/Foundation.h>
#interface AKSClassA : NSObject<NSCoding>
// declared some property
#property (nonatomic,assign) NSInteger userID;
#property (nonatomic,strong) NSString *userName;
#end
#import "AKSClassA.h"
#implementation AKSClassA
#synthesize userID;
#synthesize userName;
-(id)initWithCoder:(NSCoder *)aDecoder{
if (self = [super init]) {
self. userID = [aDecoder decodeIntegerForKey:#"userID"];
self. userName = [aDecoder decodeObjectForKey:#"userName"];
}
return self;
}
-(void)encodeWithCoder:(NSCoder *)aCoder{
[aCoder encodeInteger:userID forKey:#"userID"];
[aCoder encodeObject:userName forKey:#"userName"];
}
#end
// in some class if you are using classA object member to store and retrieve with value example below
// to save data in NSUserDefaults
AKSClassA *obj =[array1 objectAtIndex:index];
[[NSUserDefaults standardUserDefaults] saveCustomObject:button key:#"userData"];
// to retrieve data
AKSClassA *obj1 = (AKSClassA*)[[NSUserDefaults standardUserDefaults]loadCustomObjectWithKey:#"userData"];
[titleLabel setText:obj1.userName];