How do I save user preferences for my iPhone app?

Question

The question title pretty much gives it away - I'd like my app to remember a few things. It's some sort of calculator, so it should save the last used values and some user selectable settings.

Basically I'd like to save a handful of floats and BOOLs and load them again the next time the app loads.

What's the best and easiest way to do that?

Thanks!!

Answer 1

One of the easiest ways would be saving it in the NSUserDefaults:

Setting:

NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];  [userDefaults setObject:value                   forKey:key]; // – setBool:forKey: // – setFloat:forKey:   // in your case  [userDefaults synchronize]; 

Getting:

[[NSUserDefaults standardUserDefaults] objectForKey:key];  – boolForKey: 

and

– floatForKey: in your case.

Answer 2

Besides the very good NSUserDefaults approach, there is another easy way to store data from an NSArray,NSDictionary or NSData in a file. You can use these methods as well:

- (BOOL)writeToFile:(NSString *)path atomically:(BOOL)flag 

respectively (for a NSDictionary):

+ (id)dictionaryWithContentsOfFile:(NSString *)path 

you just have to give a valid path to a location. According to the iOS Application Programming Guide, the /Library/Caches directory would be the best place to store data that you need to persist between app launches. (see here)

In order to store/load a dictionary from a filed called "managers" in your document directoy you could use these methods:

-(void) loadDictionary {     //get the documents directory:     NSArray *paths = NSSearchPathForDirectoriesInDomains (NSCachesDirectory, NSUserDomainMask, YES);     NSString *cacheDirectory = [paths objectAtIndex:0];     //create a destination file name to write the data :     NSString *fullFileName = [NSString stringWithFormat:@"%@/managers", cacheDirectory];     NSDictionary* panelLibraryContent = [NSDictionary dictionaryWithContentsOfFile:fullFileName];     if (panelLibraryContent != nil) {         // load was successful do something with the data...     } else {         // error while loading the file     }    }  -(void) storeDictionary:(NSDictionary*) dictionaryToStore {     //get the documents directory:     NSArray *paths = NSSearchPathForDirectoriesInDomains     (NSCachesDirectory, NSUserDomainMask, YES);     NSString *cacheDirectory = [paths objectAtIndex:0];     //make a file name to write the data to using the     //cache directory:     NSString *fullFileName = [NSString stringWithFormat:@"%@/managers", cacheDirectory];      if (dictionaryToStore != nil) {         [dictionaryToStore writeToFile:fullFileName atomically:YES];     } }  

Anyway this approach is very limited and you have to spend a lot of extra work if you want to store more complex data. In that case the CoreData API is very very handy.