how to change ContentOffSet of UIScrollView Xcode - ios

Question

I create one UIScrollView with programmatically code and I have one button in my view (not exist in UIScrollView).
when I click on this button go to next page with modal transition. I create Cancel button in next page that when I click on it back to main page (this page have UIScrollView).
I want when click on Cancel button and return to main page call one method that is in main page and in this method change ContentOfSet my ScrollView... but not working!!!!
this is my code:
mainView.m
- (void)viewDidLoad{
UIScrollView *scrollbar = [[UIScrollView alloc] initWithFrame:CGRectMake(0,0,width, height)];
scrollbar.directionalLockEnabled = YES;
scrollbar.backgroundColor = [UIColor whiteColor];
scrollbar.maximumZoomScale = 1.0;
scrollbar.minimumZoomScale = 1.0;
scrollbar.clipsToBounds = YES;
scrollbar.showsHorizontalScrollIndicator = YES;
scrollbar.pagingEnabled = YES;
[scrollbar setContentSize:CGSizeMake(scrollbar.frame.size.width * 4,scrollbar.frame.size.height)];
scrollbar.contentOffset = CGPointMake(0, 0);
scrollbar.delegate = self;
[self.view addSubview:scrollbar];
[super viewDidLoad];
}
-(void)ChangeMainScrollContentOffset{
scrollbar.contentOffset = CGPointMake(scrollbar.frame.size.width * (3), 0);
}
this button is in root View :
- (IBAction)AddView:(id)sender{
AddStationController *add = [[AddStationController alloc]initWithNibName:#"AddStationController" bundle:nil];
[add setModalTransitionStyle:UIModalTransitionStyleCoverVertical];
[self.view.window.rootViewController presentViewController:add animated:YES completion:nil];
}
this button is Cancel button for return in my mainView:
- (IBAction)BackView:(id)sender{
mainView *main = [[mainView alloc]init];
[main ChangeMainScrollContentOffset];
[self dismissViewControllerAnimated:YES completion:nil];
}
please guide me about that!!!
I so confused why not working ContentOffSet!!!

Answer 1

I think your problem is that you didn't add ChangeMainScrollContentOffset
method to your ViewController.h file.
Just add it in ViewController.h file and than call it.

Answer 2

You second viewController should have reference to previous view controller.
When you do this:
mainView *main = [[mainView alloc]init];
[main ChangeMainScrollContentOffset];
You create another instance of mainView which not on screen and change contentOffset on ANOTHER scrollView :)
You should add property delegate to your AddStationController
AddStationController.h
#property (nonatomic, weak) mainView* delegate;
mainView:
- (IBAction)AddView:(id)sender{
AddStationController *add = [[AddStationController alloc]initWithNibName:#"AddStationController" bundle:nil];
>> add.delegate = self; <<
[add setModalTransitionStyle:UIModalTransitionStyleCoverVertical];
[self.view.window.rootViewController presentViewController:add animated:YES completion:nil];
}
Cancel button action
- (IBAction)BackView:(id)sender{
>> [self.delegate ChangeMainScrollContentOffset]; <<
[self dismissViewControllerAnimated:YES completion:nil];
}