Question

I need to call removeObject in one of my methods, but I can’t figure out how to do this correctly. I’m very new to Objective-C, and am still learning the basics. I have an app that behaves somewhat like a photo gallery, and displays UIImageViews. I’m implementing the option to have the user delete photos from their gallery. To accomplish this, I decided to place an invisible button over each picture. When the user hits an “Edit” button, the hidden delete button over each picture becomes active (I’m using the same IBOutlet over each of the hidden buttons, for simplicity). When the user taps the button over the picture, an alert view appears asking if they really want to delete it. If they click yes, deleteAlertView comes into play:

- (void)deleteAlertView:(UIAlertView *)deleteButtonPressed
       didDismissWithButtonIndex:(NSInteger)buttonIndex {
    if (buttonIndex != [deleteButtonPressed cancelButtonIndex]) {
        [array removeObject:@"%@", deleteButtonPressed];
    }

The issue here is [array removeObject:@"%@", deleteButtonPressed];, I did the %@ so that this will automatically determine which object in the array was tapped, rather than manually putting in a new method and button for each UIImageView (I may have to end up doing that). I’m getting errors regarding “array” and “deleteButtonPressed” (use of undeclared identifier), I can’t for the life of me figure out what to put instead. I’m still learning the basics and how inheritance in this language works. Any help or advice would be great! I should probably post the whole view controller file to show the related inheritance:

 - (IBAction)grabImage {
    self.imgPicker = [[UIImagePickerController alloc] init];
    self.imgPicker.delegate = self;
    self.imgPicker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;

    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPad) {
        _popover = [[UIPopoverController alloc] initWithContentViewController:imgPicker];
        [_popover presentPopoverFromRect:self.imageView.bounds inView:self.imageView permittedArrowDirections:UIPopoverArrowDirectionAny animated:YES];
    } 

    else {
        [self presentModalViewController:imgPicker animated:YES];
    }
    [self.imgPicker resignFirstResponder];
}
// Sets the image in the UIImageView
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)img editingInfo:(NSDictionary *)editInfo {
    if (imageView.image == nil) {
        imageView.image = img;
        [picker dismissModalViewControllerAnimated:YES];
        [self.popover dismissPopoverAnimated:YES];
        return;

    }

    if (imageView2.image == nil) {
        imageView2.image = img;
        [picker dismissModalViewControllerAnimated:YES];
        [self.popover dismissPopoverAnimated:YES];
        return;
    }
    if (imageView3.image == nil) {
        imageView3.image = img;
        [picker dismissModalViewControllerAnimated:YES];
        [self.popover dismissPopoverAnimated:YES];
        return;
    }
}

- (void)viewWillAppear:(BOOL)animated
{

    self.user = [NSUserDefaults standardUserDefaults];

    NSMutableArray* array = [[self.user objectForKey:@"images"]mutableCopy];
    while(array == nil)
    {
        [self.user setObject:[NSMutableArray arrayWithObject:@""] forKey:@"images"];
        array = [[self.user objectForKey:@"images"]mutableCopy];
        NSLog(@"%@",@"attempting to create an array to store the images in");
    }

}

- (void)applicationDidEnterBackground:(UIApplication*)application {
    NSLog(@"Image on didenterbackground: %@", imageView);
    NSMutableArray* array = [NSMutableArray arrayWithObject:[NSData dataWithData:UIImagePNGRepresentation(imageView.image)]];

    [array addObject:[NSData dataWithData:UIImagePNGRepresentation(imageView2.image)]];
     [array addObject:[NSData dataWithData:UIImagePNGRepresentation(imageView3.image)]];

            [self.user setObject:array forKey:@"images"];
    [user synchronize];

            }

- (void)viewDidLoad
    {
        self.user = [NSUserDefaults standardUserDefaults];
        NSLog(@"It is %@", self.user);
        NSMutableArray* array = [[self.user objectForKey:@"images"]mutableCopy];
        imageView.image = [[UIImage alloc] initWithData:[array objectAtIndex:0]];
        imageView2.image = [[UIImage alloc] initWithData:[array objectAtIndex:1]];
        imageView3.image = [[UIImage alloc] initWithData:[array objectAtIndex:2]];


        UIApplication *app = [UIApplication sharedApplication];
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(applicationDidEnterBackground:)
                                                     name:UIApplicationDidEnterBackgroundNotification
                                                   object:app];

        backToGalleryButton.hidden = YES;
        tapToDeleteLabel.hidden = YES;
        deleteButton1.hidden = YES;
        [super viewDidLoad];

    }

     - (IBAction)deleteButtonPressed:(id)sender {
    UIAlertView *deleteAlertView = [[UIAlertView alloc] initWithTitle:@"Delete"
                                                              message:@"Are you sure you want to delete this photo?"
                                                             delegate:self
                                                    cancelButtonTitle:@"Yes"
                                                    otherButtonTitles:@"No", nil];
    [deleteAlertView show];

}

- (void)deleteAlertView:(UIAlertView *)deleteButtonPressed
       didDismissWithButtonIndex:(NSInteger)buttonIndex {
    if (buttonIndex != [deleteButtonPressed cancelButtonIndex]) {
        [array removeObject:@"%@", deleteButtonPressed];
    }       

}

Answer 1

The issue here is [array removeObject:@"%@", deleteButtonPressed];

Yes, that is one of the issues (even ignoring the invalid syntax). The array does not contain your UIAlertView, it contains whatever objects [user objectForKey:@"images"] contains. Which seem like they should be NSData instances and which in any case are definitely not your UIAlertView instance(s).

So in other words, you can’t pass the UIAlertView to the array in order to have the array magically work out what item the UIAlertView is supposed to correspond to. Instead what you should do is tag the UIAlertView with the index it corresponds to when you create it. You can do this like:

UIAlertView *deleteAlertView = [[UIAlertView alloc] initWithTitle:@"Delete"
                                                              message:@"Are you sure you want to delete this photo?"
                                                             delegate:self
                                                    cancelButtonTitle:@"Yes"
                                                    otherButtonTitles:@"No", nil];
int imageIndex = <figure out the index of the associated array element based upon 'sender'>;
deleteAlertView.tag = imageIndex;

…and then when the button is pressed, you do:

[array removeObjectAtIndex:deleteButtonPressed.tag];

And to fix up that “undeclared identifier” issue, you should declare array in your header and not in viewDidLoad. You want it to be a private instance variable, not a local variable.

Also note that deleting an element from [[user objectForKey:@"images"] mutableCopy] will not automatically cause the corresponding element to be deleted from [user objectForKey:@"images"]. You need to write the modified array back to [NSUserDefaults standardUserDefaults] if you want the modification to actually persist.