Question

I am making a simple slideshow view within my app. I’d like to link my UIPageControl to my UIScrollView. This shouldn’t be too difficult, but I haven’t been able to find a simple solution anywhere. Below is my code.

HelpViewController.h

#import <UIKit/UIKit.h>

@interface HelpViewController : UIViewController{
}
@end

HelpViewController.m

#import "HelpViewController.h"

@interface HelpViewController ()

@end

@implementation HelpViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    CGRect scrollViewFrame = CGRectMake(0, 62, 320, 404);
    UIScrollView *scrollView = [[UIScrollView alloc] initWithFrame:scrollViewFrame];
    [self.view addSubview:scrollView];
    CGSize scrollViewContentSize = CGSizeMake(640, 404);
    [scrollView setContentSize:scrollViewContentSize];
    UILabel *label  = [[UILabel alloc] initWithFrame:CGRectMake(200, 200, 50, 21)];
    [label setText:@"Hello"];
    [scrollView addSubview:label];
    [scrollView setPagingEnabled:YES];
    scrollView.showsHorizontalScrollIndicator = NO;
    UIPageControl *pageControl = [[UIPageControl alloc] init]; 
    pageControl.frame = CGRectMake(110,5,100,100); 
    pageControl.numberOfPages = 2; 
    pageControl.currentPage = 0; 
    [self.view addSubview:pageControl];
    pageControl.backgroundColor = [UIColor redColor];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

@end

Answer 1

Maybe this works for you

Don’t forget to set the UIScrollView’s delegate = self (or wherever you have the selector below).

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    CGFloat pageWidth = self.scrollView.frame.size.width; // you need to have a **iVar** with getter for scrollView
    float fractionalPage = self.scrollView.contentOffset.x / pageWidth;
    NSInteger page = lround(fractionalPage);
    self.pageControl.currentPage = page; // you need to have a **iVar** with getter for pageControl
}

For your code it then would be:

.h file

#import <UIKit/UIKit.h>

@interface HelpViewController : UIViewController{
}

@property (nonatomic, retain) UIScrollView *scrollView;
@property (nonatomic, retain) UIPageControl * pageControl;
@end

.m file

#import "HelpViewController.h"

@interface HelpViewController ()

@end

@implementation HelpViewController
@synthesize scrollView=scrollView_;
@synthesize pageControl=pageControl_;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    CGRect scrollViewFrame = CGRectMake(0, 62, 320, 404);
    self.scrollView = [[[UIScrollView alloc] initWithFrame:scrollViewFrame] autorelease];
    self.scrollView.delegate = self;
    [self.view addSubview:self.scrollView];
    CGSize scrollViewContentSize = CGSizeMake(640, 404);
    [self.scrollView setContentSize:scrollViewContentSize];
    UILabel *label  = [[UILabel alloc] initWithFrame:CGRectMake(200, 200, 50, 21)];
    [label setText:@"Hello"];
    [self.scrollView addSubview:label];
    [self.scrollView setPagingEnabled:YES];
    self.scrollView.showsHorizontalScrollIndicator = NO;
    self.pageControl = [[[UIPageControl alloc] init] autorelease]; 
    self.pageControl.frame = CGRectMake(110,5,100,100); 
    self.pageControl.numberOfPages = 2; 
    self.pageControl.currentPage = 0; 
    [self.view addSubview:self.pageControl];
    pageControl.backgroundColor = [UIColor redColor];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

 - (void)scrollViewDidScroll:(UIScrollView *)scrollView {
        CGFloat pageWidth = self.scrollView.frame.size.width;
        float fractionalPage = self.scrollView.contentOffset.x / pageWidth;
        NSInteger page = lround(fractionalPage);
        self.pageControl.currentPage = page; 
    }


@end