Looping through on NSArray objects with button taps - ios

Question

I have an array of NSStrings, what I'd like to use as a source for a UIImageView's image names.
When the user taps a button I load a new image - next object from the array - into the same image view, that would be the final goal. Actually I have a working, but silly solution, and that's not what I want. I would like to load the string names from an array to the UIImage, because this if statement can grow really big with 30-40 object and that's not so reliable. I'm not so fine with for loops so I would really appreciate if somebody could show me how can I get the same result with a loop or any other way.
- (IBAction)changeImage:(id)sender {
if (!self.userImageView.image) {
UIImage *image = [UIImage imageNamed:#"img1.png"];
self.userImageView.image = image;
self.currentDisplayedImageString = #"img1.png";
// self.currentDisplayedImageString is an ivar, type of NSString
}
else {
if ([self.currentDisplayedImageString isEqualToString:#"img1.png"]) {
UIImage *image = [UIImage imageNamed:#"img2.png"];
self.userImageView.image = image;
self.currentDisplayedImageString = #"img2.png";
}
if ([self.currentDisplayedImageString isEqualToString:#"img2.png"]) {
UIImage *image = [UIImage imageNamed:#"img3.png"];
self.userImageView.image = image;
self.currentDisplayedImageString = #"img3.png";
}
// AND SO ON...
}
}

Answer 1

something like:
#interface ViewController ()
#property (strong, nonatomic) UIImageView *imageView;
#property (strong, nonatomic) NSArray *imageNames;
#property (assign, nonatomic) int currentImageIndex;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
self.imageNames = #[#"img1", #"img2", #"img3", #"img4"];
self.currentImageIndex = -1;
}
- (void)changeImage {
if (++self.currentImageIndex == self.imageNames.count) {
self.currentImageIndex = 0;
}
self.imageView.image = [UIImage imageNamed:self.imageNames[self.currentImageIndex]];
}
#end
hope it helps!

Answer 2

If your image names are in fact "img1," "img2," "img3," etc. you don't actually need an array to store them since the names essentially index themselves. Instead I'd recommend doing something like:
- (IBAction)changeImage:(id)sender {
if (!self.userImageView.image ||
[self.currentDisplayedImageString isEqualToString:#"img40.png"]) {
self.currentDisplayedImageString = #"img1.png";
}
else {
// Get the filename's numerical index by parsing out the numerical component
NSString *index = [[self.currentDisplayedImageString componentsSeparatedByCharactersInSet:
[[NSCharacterSet decimalDigitCharacterSet] invertedSet]]
componentsJoinedByString:#""];
// "Increment" the currentDisplayedImageString
self.currentDisplayedImageString = [NSString stringWithFormat:#"img%#.png", index];
}
// Then update the image
UIImage *image = [UIImage imageNamed:currentDisplayedImageString];
self.userImageView.image = image;
}