Question

I’ve looked over many code samples here and on other sites but I couldn’t find examples relevant to this particular situation and so I thought I would try asking.

My application is using the utility application template (a main view and a flipside view) with Automatic Reference Counting (ARC) enabled.

On the flipside view, I have an empty UITableView with a navigation bar with a “Done” button that returns you to the main view and an “Add” button. Clicking the “Add” button creates an empty row and activates the UIImagePicker. After selecting a photo from the UIImagePicker, that photo is passed into the new cell’s imageView.

My problem is that, after adding a new row to the table, when I switch to the main view then back to the flipside view, the table is empty again.

I think this has to do with how I am writing the images to my NSMutableArray.

If anyone knows how I can keep the UITableView from getting wiped when switching views, that would be fantastic.

Thanks in advance,

Stephen

AppDelegate.h

#import <UIKit/UIKit.h>

@class MainViewController;

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@property (strong, nonatomic) MainViewController *mainViewController;

@end

AppDelegate.m

#import "AppDelegate.h"

#import "MainViewController.h"

@implementation AppDelegate

@synthesize window = _window;
@synthesize mainViewController = _mainViewController;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{    
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    self.mainViewController = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
    self.window.rootViewController = self.mainViewController;
    [self.window makeKeyAndVisible];
    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application
{
    /*
     Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
     Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
     */
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    /*
     Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
     If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
     */
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    /*
     Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
     */
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    /*
     Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
     */
}

- (void)applicationWillTerminate:(UIApplication *)application
{
    /*
     Called when the application is about to terminate.
     Save data if appropriate.
     See also applicationDidEnterBackground:.
     */
}

@end

MainViewController.h

#import "FlipsideViewController.h"

@interface MainViewController : UIViewController <FlipsideViewControllerDelegate>

- (IBAction)showInfo:(id)sender;

@end

MainViewController.m

#import "MainViewController.h"

@implementation MainViewController

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)viewDidUnload
{
    [super viewDidUnload];
}

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

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

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

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

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

#pragma mark - Flipside View

- (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller
{
    [self dismissModalViewControllerAnimated:YES];
}

- (IBAction)showInfo:(id)sender
{    
    FlipsideViewController *controller = [[FlipsideViewController alloc] initWithNibName:@"FlipsideViewController" bundle:nil];
    controller.delegate = self;
    controller.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
    [self presentModalViewController:controller animated:YES];
}

@end

FlipsideViewController.h

#import <UIKit/UIKit.h>

@class FlipsideViewController;

@protocol FlipsideViewControllerDelegate
- (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller;
@end

@interface FlipsideViewController : UIViewController <UIActionSheetDelegate, UIAlertViewDelegate, UIImagePickerControllerDelegate,UINavigationControllerDelegate>
{
NSMutableArray *dataArray;
IBOutlet UITableView *tableView;
IBOutlet UIBarButtonItem *addPhotoButton;
UITableViewCell *addedCell;
UIImage *image;
UIImagePickerController *imagePicker;
}

@property (nonatomic, strong) NSMutableArray *dataArray;
@property (nonatomic, strong) IBOutlet UITableView *tableView;
@property (nonatomic, strong) IBOutlet UIBarButtonItem *addPhotoButton;
@property (nonatomic, strong) UITableViewCell *addedCell;
@property (nonatomic, strong) UIImage *image;
@property (nonatomic, strong) UIImagePickerController *imagePicker;

@property (weak, nonatomic) IBOutlet id <FlipsideViewControllerDelegate> delegate;

- (IBAction)addPhoto:(id)sender;
- (IBAction)done:(id)sender;
@end

FlipsideViewController.m

#import "FlipsideViewController.h"
#import "MainViewController.h"

@implementation FlipsideViewController

@synthesize delegate = _delegate;
@synthesize dataArray, tableView, addPhotoButton, addedCell, image, imagePicker;

- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
[super viewDidLoad];

self.dataArray = [[NSMutableArray alloc] init];
self.imagePicker = [[UIImagePickerController alloc] init];
self.imagePicker.allowsEditing = NO;    
self.imagePicker.delegate = self;   
self.imagePicker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
}

#pragma mark - UITableView delegate methods

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return self.dataArray.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *kCellID = @"cellID";

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:kCellID];
if (cell == nil)
{
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:kCellID];
cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
cell.showsReorderControl = YES;
}

return cell;
}

- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}

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

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

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

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

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
// Return YES for supported orientations
return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

#pragma mark - Actions

- (IBAction)addPhoto:(id)sender
{
[self presentModalViewController:self.imagePicker animated:YES];
}


- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)img editingInfo:(NSDictionary *)editInfo {
// AppDelegate* appDelegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
// appDelegate.pickerImage = img;

image = img;
[self dismissModalViewControllerAnimated:YES];

[self.tableView beginUpdates]; 
[self.dataArray addObject:@""];
NSArray *paths = [NSArray arrayWithObject:[NSIndexPath indexPathForRow:(self.dataArray.count - 1) inSection:0]];
[self.tableView insertRowsAtIndexPaths:paths withRowAnimation:NO];
[self.tableView endUpdates];

addedCell = [self.tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:(self.dataArray.count - 1) inSection:0]];
addedCell.imageView.image = image;
[self.tableView reloadData];
}

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
NSUInteger row = [indexPath row];
[self.dataArray removeObjectAtIndex:row];
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
}

- (IBAction)done:(id)sender
{
[self.delegate flipsideViewControllerDidFinish:self];
}
@end

Answer 1

You need to ask yourself questions, because this is a logic problem.

how do you create your FlipsideViewController in the MainViewController?

Are you creating a new one each time, if yes or no what are the reason for that?

How are you keeping alive the data?

There is a least 3 or 4 ways that could happen, and principally it would be in our MainViewController.

If those question don’t help you, please post the MainViewController code.

---

- (IBAction)showInfo:(id)sender  // this is trigger by IB
{    
//This is created each time
FlipsideViewController *controller = [[FlipsideViewController alloc] initWithNibName:@"FlipsideViewController" bundle:nil];  
controller.delegate = self;
controller.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;

// HERE the 'controller' get retain by self and you don't have reference to it anymore,
[self presentModalViewController:controller animated:YES]; 

// So when the ModalView is finish your controller will be trash with all it's data
// If you don't hold on to something it will go away, thanks to ARC
}

The problem is about life cycle of your objects

If you think that the user will ofter go to your FlipsideView you could create it once and keep it in a property of your MainView.
If not you could cache the Array in the MainView and pass it to the Flipside just after creating it.
(In both case if you want to have persistence between application launches you will need to save your mutable array to disk. And if you save it to disk it also could be the Flipside that goes directly to disk to fetch the information)

I would suggest any new Apple programmer to study and understand the memory management of the retain and release.
Because ARC is no magic and it’s stand for Automatic Reference Counting. If you understand how the retain and release work, you will have a better understanding of how ARC works and be able to clearly see the life cycle of your objects.
(And actually ARC is doing retain and release under the hood)