Objective C iPhone Development, saving and retrieving an NSMutableArray

Question

I am new to iPhone development and I am using XCode 4.2 I am trying to save an NSMutable array so that when I close the application and reopen it , the data will still be there I am using these two functions :

-(void)saveData{
    [NSKeyedArchiver archiveRootObject:[data copy] toFile:[self dataFilePath]];
}
- (void)loadData
{
    data = [NSKeyedUnarchiver unarchiveObjectWithFile:self.dataFilePath];
}

but I found two major issues : 1- when I switch views and come back , the data is gone 2- when I completely exit the application (ie I double click on the Main button and remove it from the list of running application) the data is not erased as well

I found that I can use these two NSMutableArray methods : writeToFile and initWithContentsOfFile but I don t know where to call them (is it when I add items to the UITableView ? in the viewDidLoad ?

can somebody give me a sample code?

Thanks in advance

Answer 1

For saving an array use writeToFile:atomically: method. It will save your NSArray content as plist file. For load an array from plist file, use initWithContentsOfFile: method.

Please note, that these methods will be able to save your stuff, only if your array has the following class instances NSString , NSData , NSDate , NSNumber NSArray , or NSDictionary as items.

you can call save/load methods like following

// in view controller implementation

- (void) saveData {
  [self.theArray writeToFile: self.filePath automatically:NO];
}

- (void) loadData {
  self.theArray = [NSArray arrayWithContentsOfFile: self.filePath];
}

- (void) viewDidLoad {
  [super viewDidLoad];

  [self loadData];
}

- (void) viewWillDisappear: (BOOL) animated {
  [super viewWillDisappear: animated];

  [self saveData];
}


// in the UIApplicationDelegate implementation
- (void)applicationWillResignActive:(UIApplication *)application {
  [myCustomController saveData];
}

Answer 2

The problem is that when those 2 actions happen, saveData is not getting called. Therefore I would suggest saving your data on the AppDelegate on this method to solve problem 2 (exit app)

- (void)applicationDidEnterBackground:(UIApplication *)application
{
//Save data
}

As for problem 1 (when switching views), you just need to call your saveData on this method on your viewController:

- (void)viewWillDisappear:(BOOL)animated
{
   //Save data
}

Hope that helps.