Moving previous image in ScrollView using button click - iphone

Question

When I press previous button it does not take any effect. Next Button is working properly but previous button do not show previous image. I am using scroll view to load images:
- (IBAction)next{
int arraycount = [appDelegate.articles count];
for (int nextIndex = [pageControl currentPage]; nextIndex < arraycount; nextIndex++) {
if ( self.scrollView.contentOffset.x <= self.scrollView.frame.size.width ) {
CGRect frame;
frame.origin.x = self.scrollView.contentOffset.x + self.scrollView.frame.size.width;
frame.origin.y = 0;
frame.size = self.scrollView.frame.size;
[self.scrollView scrollRectToVisible:frame animated:YES];
pageControlBeingUsed = YES;
}
}
}
-(IBAction)previousButtonAction
{
int arraycount = [appDelegate.articles count];
NSLog(#" arraycount : %d", arraycount);
NSLog(#" [pageControl currentPage] : %d", [pageControl currentPage]);
for (int nextIndex = [pageControl currentPage]; nextIndex>arraycount; nextIndex--) {
if ( self.scrollView.contentOffset.x >= self.scrollView.frame.size.width ) {
CGRect frame;
frame.origin.x = self.scrollView.contentOffset.x + self.scrollView.frame.size.width;
frame.origin.y = 0;
frame.size = self.scrollView.frame.size;
[self.scrollView scrollRectToVisible:frame animated:YES];
pageControlBeingUsed = YES;
}
}
}

Answer 1

Okay, I now think I would approach this differently. I would check the current offset before re-assigning it.
untested code:
- (IBAction)next{
if ( self.scrollView.contentOffset.x <= self.scrollView.frame.size.width ) {
CGRect frame;
frame.origin.x = self.scrollView.contentOffset.x + self.scrollView.frame.size.width;
frame.origin.y = 0;
frame.size = self.scrollView.frame.size;
[self.scrollView scrollRectToVisible:frame animated:YES];
pageControlBeingUsed = YES;
}
}

Answer 2

I would disable the "next" button when the user gets to the third image. If you prefer to return to the first image when the user presses "next" in the third image, then you must add an additional else after your if to indicate that case:
- (IBAction)next{
int arraycount = [appDelegate.articles count];
for (int nextIndex = [pageControl currentPage]; nextIndex < arraycount; nextIndex++) {
if (nextIndex < arraycount) {
CGRect frame;
frame.origin.x = self.scrollView.frame.size.width * nextIndex;
frame.origin.y = 0;
frame.size = self.scrollView.frame.size;
[self.scrollView scrollRectToVisible:frame animated:YES];
pageControlBeingUsed = YES;
}
// If the user clicks on next in the last item, return to the first
else {
CGRect frame;
frame.origin.x = 0;
frame.origin.y = 0;
frame.size = self.scrollView.frame.size;
[self.scrollView scrollRectToVisible:frame animated:YES];
pageControlBeingUsed = YES;
}
}
}

Answer 3

arraycount = 3
[pageControl currentPage] is zero indexed so when you are on page 3 it equals 2.
so the start of your for loop nextIndex equals 2 which is less than arrayCount so it gets into your loop.
change it to:
for (int nextIndex = [pageControl currentPage]; nextIndex < (arraycount-1); nextIndex++) {
okay what does this output:
- (IBAction)next{
int arraycount = [appDelegate.articles count];
NSLog(#" arraycount : %d", arraycount);
NSLog(#" [pageControl currentPage] : %d", [pageControl currentPage]);
for (int nextIndex = [pageControl currentPage]; nextIndex < (arraycount-1); nextIndex++) {
NSLog(#" nextIndex : %d", nextIndex);
CGRect frame;
frame.origin.x = self.scrollView.frame.size.width * nextIndex;
frame.origin.y = 0;
frame.size = self.scrollView.frame.size;
[self.scrollView scrollRectToVisible:frame animated:YES];
pageControlBeingUsed = YES;
}
}

Answer 4

Fo me it is working in swift 3.
func prevAction (sender:UIButton)
{
print("self.scView.contentOffset.x ..\(self.scView.contentOffset.x)")
if ( self.scView.contentOffset.x <= self.scView.contentSize.width )
{
var frame = CGRect()
frame.origin.x = self.scView.contentOffset.x - 80;
frame.origin.y = 0;
frame.size = self.scView.frame.size;
self.scView .scrollRectToVisible(frame, animated: true)
}
}
Thanks to #ader.