UIImageView crashes due to memory warning, trying to load a huge array of images

Question

I am making an application just like a movie player but instead of showing a video, I have the movie in image frames. A slider is used to move the "movie" forward and backward and if released, the "movie" is auto played up to a chapter. I accomplish this by having a UIImageView and changing the image property on each value change of the slider. After a while the app crashes due to memory warning. I cannot use the animation of UIImage because I want to control the position (aka visible image/frame) by scrubbing the slider. So I have an ImageManager class that loads all the image names in string in an array (total 1500 images of about 150kb each) on init.

- (id) initWithCanvas:(UIImageView*) canvasView{
    self = [super init];
    if (self) {
        totalImages = 1500;
        self.canvas = canvasView;
        self.images = [[NSMutableArray alloc] init];
        for (int i=0; i<totalImages; i++){
            [self.images addObject:[NSString stringWithFormat:@"frame_%04d.jpg", i]]; 
            i = i + 4; // I use this to skip 4 frames
        }
        previewsImageIndex = -1;
        [self setImageAtPosition:0];
    }
    return self;
}

Then I have a function that is fired on value change of the UISlider which finds the current image name and constructs a UIImage from the image name and sets it to the UIImageView

- (void) setImageAtPosition:(CGFloat)percentage{
    currentImage = nil;
    int position = percentage * [self.images count];
    if (position != previewsImageIndex){
        previewsImageIndex = position;
        NSLog(@"Got image:%d at percentage: %f", position, percentage);
        if (position < [self.images count]){
            self.canvas.image = nil;
            currentImage = [UIImage imageNamed:[self.images objectAtIndex:position]];
            [self.canvas setImage:currentImage];
            currentImage = nil;
            //[currentImage release];
        }
    }
}

Even though I set the currentImage and the canvas.image as nil, still after a while the app crashes. I don't understand where am I having a memory leak. Also, I code with ARC, so no releasing.

Is there any other better way to do it, other than having a UIImage view? I want frame-by-frame view ability and the MPMoviePlayer or AVPlayer cannot do that fine-grained scrubbing.

Answer 1

You will want to use the [UIImage imageWithContentsOfFile:@""] method, as that doesn't cache images. imageNamed: caches any images that are loaded through it.