NSMutableArray Difficulty

If you wanna see the code Im having problem with, here is the link:

My question is connected with my past question.

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  • I’m really having problem with my NSMutableArray, I’m currently using iCarousel for my slotMachine object(slot1 and slot2). My app works this way:

    From PhotoViewController I made a view that has thumbnail images, then assign its frame with button. So if 1 image was pressed, it will save that integer via NSUserDefaults.
    Then I will retrieve it in my carouselViewController

    Im thinking of adjusting the array but I can’t.
    I also have tried my question here:
    Comparing with NSMutableArray
    If only I can do it the same as Array 2 it would be much easy, but still not working.


    I have done it this way, have a Viewcontroller that contains the UIImageView with a button in it, so when the user taps it, my CustomPicker pops up. My CustomPicker contains the image on what the user have picked on the camera roll. So each button has a specific value sent to my iCarouselView using NSUserDefaults. carousel1 for First slot and carousel2 for Second slot.

    Here is what I wanna do: I want to forcefully make it stop to the index the user picks. (Which Im doing in my carouselDidEndScrollingAnimtaion)

    In my carouselDidEndScrollingAnimation method i tested all of my condition(individually) it works perfectly in terms of comparing.
    Then when I combine the conditions, the first Two comparison or STOP is RIGHT, but the next two are always wrong. Or sometimes Got mixed up.

    I need to scroll the two specific indexes/integer which was User Picked( I already done that) was able to scroll 2 pairs of them but then the next two were always wrong because I think there indexes were adjusting.


    Image Below is my PhotoViewController which contained the Comparing Stage SETTING of my game.UIImageVIew with UIButton.Image that will be put in the number according to it will be Forcefully and should be forcefully shown.

    enter image description here

    When my iCarousel start then it stops for example in the image below(Which is not the same as the above):
    enter image description here

    Will be forcefully scroll to the inputted image in the PhotoViewController

    enter image description here

    Its like this. I have a settingsView from there, I will import my images(Multiple) for Slot1 & Slot2.
    Then in another View the PhotoViewController that is where the image above is shown. THe first column corresponds to 1st slot followed by the 2nd slot. if a view is pressed (for example No. 1 of Slot 1 it will load a thumbnail of images loading the images picked from Picker for the Slot 1.

    You will have to do it 4 times(pair) —-> The displayed here I get their indexes via NSUserDefaults via button.tag then send to iCarouselView.

    Then when you are done (pressed Done button) it will go to iCarouselView then, as shown above thats the view of it.
    When pressed it will spin for couple of seconds, then when finished but not stop at the user picked in the PhotoView it will forcefully scroll to that index.


    Is there a way to make my array or my iCarousel.view not adjust their indexes when Im deleting. To still retain my indexes the right way. Or are there other solution like adjusting my array, the same as adjusting my PhotoViewController picked indexes too. Because I think that when my array retain their indexes even deleting I would be able to solve this problem. But still can’t.

    Hope you understand my question.

    5 Solutions Collect From Internet About “NSMutableArray Difficulty”

    Is there a way to make my array or my iCarousel.view not adjust their indexes when Im deleting. To still retain my indexes the right way. Or are there other solution like adjusting my array, the same as adjusting my PhotoViewController picked indexes too. Because I think that when my array retain their indexes even deleting I would be able to solve this problem. But still can’t.

    The only way you have to modify the way iCarousel manages its indexes is by modifying the code. Indeed, if you look at the removeViewAtIndex method in iCarousel.m, you will see that indexes are managed through an NSDictionary, and at the moment of deleting, the dictionary is rearranged (items are reordered). You could take that method:

    - (void)removeViewAtIndex:(NSInteger)index
        NSMutableDictionary *newItemViews = [NSMutableDictionary dictionaryWithCapacity:[itemViews count] - 1];
        for (NSNumber *number in [self indexesForVisibleItems])
            NSInteger i = [number integerValue];
            if (i < index)
                [newItemViews setObject:[itemViews objectForKey:number] forKey:number];
            else if (i > index)
                [newItemViews setObject:[itemViews objectForKey:number] forKey:[NSNumber numberWithInteger:i - 1]];
        self.itemViews = newItemViews;

    You could apply the same logic to your array, so that the carousel and your array keep in sync. Of course, if you store the indexes somewhere (slot1/slot2/slot2/slot4?), you should also update their values after removing an element.

    On the other hand, I think that what you are asking here is how to do something that you believe would solve the problem you have, but you are not really explaining what the problem is. Indeed, if I understand you correctly, what you do is:

    1. spinning the carousel;

    2. when the carousel stops, if it is not by chance on the desired item, you “force” it to scroll to that item.

    There is no reason why this should not work after deleting some elements (unless iCarousel has some bugs, then the solution would be catching the bug). The only part is knowing which index is the one you would like to move to.

    As a suggestion, I would start off by simplifying your delegate carouselDidEndScrollingAnimation method. Indeed, your carouselDidEndScrollingAnimation has a parameter called carousel, well, I think this is the only carousel you should ever be referring to in that method. If you don’t see it, this is the reasoning: each of your carousel will stop scrolling and the carouselDidEndScrollingAnimation will be called; so that method will be called twice. Each time that method is executed you will modify the state of both carousel1 and carousel2 (by calling scrollToItemAtIndex); therefore, on each carousel you will call scrollToItemAtIndex twice.

    This does no sound very correct to me. So you should find a way to scroll only carousel1 when carouselDidEndScrollingAnimation is called for carousel1 and to scroll only carousel2 when carouselDidEndScrollingAnimation is called for carousel2.

    More generally, another point I would like to raise is that the idea of:

    1. letting a carousel stop;

    2. scrolling it again so that it reaches the desired position;

    does not seem the best implementation possible since the user would see the carousel stopping and then starting over again.

    The way I would approach this is by modifying directly iCarousel implementation so that it supports this specific behavior you need.

    Concretely, give a look at the step method in iCarousel.m. This is called at each frame to produce the carousel animation. Now, in this method there is decelerating branch:

    else if (decelerating)
        CGFloat time = fminf(scrollDuration, currentTime - startTime);
        CGFloat acceleration = -startVelocity/scrollDuration;
        CGFloat distance = startVelocity * time + 0.5f * acceleration * powf(time, 2.0f);
        scrollOffset = startOffset + distance;
        [self didScroll];
        if (time == (CGFloat)scrollDuration)
            decelerating = NO;
            if ([delegate respondsToSelector:@selector(carouselDidEndDecelerating:)])
                [delegate carouselDidEndDecelerating:self];
            if (scrollToItemBoundary || (scrollOffset - [self clampedOffset:scrollOffset]) != 0.0f)
                if (fabsf(scrollOffset/itemWidth - self.currentItemIndex) < 0.01f)
                    //call scroll to trigger events for legacy support reasons
                    //even though technically we don't need to scroll at all
                    [self scrollToItemAtIndex:self.currentItemIndex duration:0.01];
                    [self scrollToItemAtIndex:self.currentItemIndex animated:YES];
                CGFloat difference = (CGFloat)self.currentItemIndex - scrollOffset/itemWidth;
                if (difference > 0.5)
                    difference = difference - 1.0f;
                else if (difference < -0.5)
                    difference = 1.0 + difference;
                toggleTime = currentTime - MAX_TOGGLE_DURATION * fabsf(difference);
                toggle = fmaxf(-1.0f, fminf(1.0f, -difference));

    and you see that when the carousel stops decelerating, it is scrolled again. This is exactly the same as you are doing, so you might find a way to modify this code and have the carousel scrolls exactly to the index you need. In this way you would get a far smoother spinning of the carousel.

    Hope this helps and apologies for the lengthy reply.

    Its a little difficult to know what the issue is here. Are you using a single NSMutableArray for the images and using the NSUserDefaults value to get the object at the index in the array?

    Im not 100% sure on what is happening. What does the user do(and in what view) and what is triggered after that(which view is presented).

    Are you trying to stop the “spinning” images on the image that is the same as the one picked from the previous view?

    According to your images above, the images are off by a single index. Is this the case every time? Maybe there is an issue with your fetching from the array.

    If you give me some more info I can help.

    I looked through the code you pasted again and I think this might be your issue

    if (twoSlot1 > [(UIImageView*)[self.carousel2 currentItemView] tag]){            
                    [self.carousel1 scrollToItemAtIndex:(-twoSlot1)-2 duration: 3.5f];
                } else {
                    [self.carousel1 scrollToItemAtIndex:-twoSlot1 duration: 3.5f];

    On all other code blocks like that you have this where you call each carousel. In the above code you call carousel 1 twice.

    if (slot2 > [(UIImageView*)[self.carousel1 currentItemView] tag]){
                [self.carousel1 scrollToItemAtIndex:(-slot2)-2 duration: 3.0f];
                } else {
                [self.carousel1 scrollToItemAtIndex:-slot2 duration: 3.0f];    
                if (twoSlot2 > [(UIImageView*)[self.carousel2 currentItemView] tag]){
                [self.carousel2 scrollToItemAtIndex:(-twoSlot2)-2 duration: 3.5f];    
                } else {
                [self.carousel2 scrollToItemAtIndex:-twoSlot2 duration: 3.5f];

    You call self.carousel1 when you should be calling number 2.

    Is this correct?

    Referring to your question. You want an array that does not change its members’ indexes when a member is deleted from the array.

    I guess you could use an NSMutableDictionary. It is an associative array so to say, where the indexes are of your choice and they remain unchanged when you delete a member from in between.
    You may still use 0..n as your Index. You can still use some methods that you are familiar with from NSArray, such as count. You can use an enumerator to go through all members of the dictionary. On the other hand you can still use your for-loops as you are used to use them with arrays. Just be prepared that a) objectForKey:i may return nil if the key/index does not exist (e.g. was deleted) and that count retuns the number of the objects but not the highest index+1 as it does with arrays.

    Not sure if I understand completely, but when one of the elements in your mutable array is deleted, rather than just deleting it, maybe insert it with another “dummy” place holder object? That way your indexes won’t change at all when a delete occurs

    I’m having a hard time understanding your overall problem, but from what I can gather the crux of your question is this:

    Is there a way to make my array or my iCarousel.view not adjust their indexes when Im deleting.

    I don’t know whether it will solve your bigger issue, but using an NSMutableDictionary to simulate an array should allow you to do this. You can simply use the indices as the keys to the dictionary, and then when you remove the item associated with an index, no other indices will be adjusted as a result. For example:

    NSMutableDictionary *arrayDict = [[NSMutableDictionary alloc] init];
    [arrayDict setValue:foo forKey:[NSNumber numberWithInt:[arrayDict count]]];
    [arrayDict setValue:bar forKey:[NSNumber numberWithInt:[arrayDict count]]];
    [arrayDict setValue:fooBar forKey:[NSNumber numberWithInt:[arrayDict count]]];

    And then you can access the object an at index with [arrayDict objectForKey:[NSNumber numberWithInt:index]].

    Note that using an NSNumber for the key parameter of setValue:forKey: will generate a warning, but you can safely ignore this (or use the string representation if it bothers you).