Storing ALAsset URLs in NSUserDefaults

Question

Hi, I have an ALAsset URL saving NSMutableArray ,

 "ALAsset - Type:Photo, URLs:assets-library://asset/asset.JPG?id=119A0D2D-C267-4B69-A200-59890B2B0FE5&ex‌​t=JPG", "ALAsset - Type:Photo, URLs:assets-library://asset/asset.JPG?id=92A7A24F-D54B-496E-B250-542BBE37BE8C&ex‌​t=JPG", "ALAsset - Type:Photo, URLs:assets-library://asset/asset.JPG?id=77AC7205-68E6-4062-B80C-FC288DF96F24&ex‌​t=JPG 

I could not save NSMutableArray in NSUserDefaults due to an error with the error Note that dictionaries and arrays in property lists must also contain only property values. I am thinking about using this:

  - (void)encodeWithCoder:(NSCoder *)encoder { //Encode properties, other class variables, etc [encoder encodeObject:self.selectedPhotos forKey:@"selectedPhotos"]; } - (id)initWithCoder:(NSCoder *)decoder { if((self = [super init])) { //decode properties, other class vars self.selectedPhotos = [decoder decodeObjectForKey:@"selectedPhotos"]; } return self; } 

then save and extract it with this code:

  - (void)saveCustomObject:(MyCustomObject *)obj { NSData *myEncodedObject = [NSKeyedArchiver archivedDataWithRootObject:obj]; NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; [defaults setObject:myEncodedObject forKey:@"myEncodedObjectKey"]; } - (MyCustomObject *)loadCustomObjectWithKey:(NSString *)key { NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; NSData *myEncodedObject = [defaults objectForKey:key]; MyCustomObject *obj = (MyCustomObject *)[NSKeyedUnarchiver unarchiveObjectWithData: myEncodedObject]; return obj; } 

But somehow I didn’t quite understand, it still crashed in my code. Do not know how. And I could not save it to NSUserDefaults. Hope someone helps. In fact, there was a problem with this. I hope someone NSUserDefaults me on the right path to salvation and returns me the right path from NSUserDefaults . Then go back to NSMutableArray .

Answer 1

NSUserDefaults accepts only a limited set of classes as objects. See the documentation . You only need to take care of storing the values ​​of these types (NSData, NSString, NSNumber, NSDate, NSArray or NSDictionary, and of course it is applied recursively) in the dictionary.

To save URLs to NSUserDefaults , save them as strings, and then read them as URLs. If you need a dictionary in the current format, you may need to convert it before saving.

 - (void) saveMyUrls { NSMutableArray* urls = [NSMutableArray arrayWithCapacity:self.myUrls.count]; for(NSURL* url in self.myUrls) { [urls addObject:[url absoluteString]]; } [[NSUserDefaults standardUserDefaults] setObject:urls forKey:@"myUrls"]; } - (void) loadUrls { NSArray* urls = [[NSUserDefaults standardUserDefaults] objectForKey:@"myUrls"]; self.myUrls = [NSMutableArray arrayWithCapacity:urls.count]; for(NSString* urlString in urls) { [self.myUrls addObject:[NSURL URLWithString:urlString]]; } [[NSUserDefaults standardUserDefaults] setObject:urls forKey:@"myUrls"]; } 

If you need to save more information than just a URL, say a user-specified label, you can save the object as an NSDictionary instead, for example.

 - (void) saveMyUrlsWithLabels { NSMutableArray* objs = [NSMutableArray arrayWithCapacity:self.myObjects.count]; for(MyObject* obj in self.myObjects) { [objs addObject:[NSDictionary dictionaryWithKeys:@"url", @"label" forObjects:obj.url.absoluteString, obj.userSpecifiedLabel]; } [[NSUserDefaults standardUserDefaults] setObject:objs forKey:@"myObjects"]; } 

Answer 2

Maybe you should do it like this:

 - (MyCustomObject *)loadCustomObjectWithKey:(NSString *)key { NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; [defaults synchronize]; // note this NSData *myEncodedObject = [defaults objectForKey:key]; MyCustomObject *obj = nil; // it would be even better // to wrap this into @ try-@catch block if(myEncodedObject) { obj = (MyCustomObject *)[NSKeyedUnarchiver unarchiveObjectWithData: myEncodedObject]; } return obj; } 

Also note that if you want to use NSKeyedArchiver and NSKeyedUNarchiver , your MyCustomObject class must conform to the NSCoding protocol. Check out the NSCoding protocol link and Programming and Serialization Guide .

Answer 3

This is another way to do this, and you can use NSUserDefaults. Basically you get the URL of the resource, save it and then convert it back to an object / image

 //SET IT ALAsset *asset3 = [self.assets objectAtIndex:[indexPath row]]; NSMutableString *testStr = [NSMutableString stringWithFormat:@"%@", asset3.defaultRepresentation.url]; //NSLog(@"testStr: %@ ...", testStr); [[NSUserDefaults standardUserDefaults] setObject:testStr forKey:@"userPhotoAsset"]; [[NSUserDefaults standardUserDefaults] synchronize]; //GET IT NSString *assetUrlStr = [[NSUserDefaults standardUserDefaults] objectForKey:@"userPhotoAsset"]; NSURL* aURL = [NSURL URLWithString:assetUrlStr]; NSLog(@"aURL: %@ ...", aURL); ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init]; [library assetForURL:aURL resultBlock:^(ALAsset *asset) { UIImage *copyOfOriginalImage = [UIImage imageWithCGImage:[[asset defaultRepresentation] fullScreenImage] scale:1.0 orientation:UIImageOrientationUp]; imgVwPortrait.image = copyOfOriginalImage; } failureBlock:^(NSError *error) { // error handling NSLog(@"failure-----"); }];