UIScrollView with horizontal paging` does not center subview - ios

Question

I am trying to use UIScrollView with paging enabled. I am adding various UIView to UISCrollView as a subviews. I want those subview to be smaller than size of scroll view so I have modified my constrains accordingly. Now when I actually swipe them left/ right then do not happened to be in center. I was expecting it to show previous / next view peeking from sides with current page in center.
This is what it looks like
Below is my code scrollview implementation
//
// ViewController.m
// Paging
//
#import "ViewController.h"
#interface ViewController ()
#property (nonatomic, strong) UIScrollView *pagingScrollView;
#end
#implementation ViewController
- (UIScrollView *)pagingScrollView {
if (!_pagingScrollView) {
_pagingScrollView = [[UIScrollView alloc] initWithFrame:CGRectZero];
_pagingScrollView.translatesAutoresizingMaskIntoConstraints = NO;
_pagingScrollView.backgroundColor = [UIColor orangeColor];
_pagingScrollView.showsHorizontalScrollIndicator = NO;
_pagingScrollView.showsVerticalScrollIndicator = NO;
_pagingScrollView.contentInset = UIEdgeInsetsZero;
_pagingScrollView.pagingEnabled = YES;
_pagingScrollView.clipsToBounds = NO;
_pagingScrollView.bounces = NO;
}
return _pagingScrollView;
}
- (void)viewDidLoad {
[super viewDidLoad];
[self scrollViewSetUp];
NSDictionary *views = NSDictionaryOfVariableBindings(_pagingScrollView);
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|[_pagingScrollView]|"
options:0
metrics:nil
views:views]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:|[_pagingScrollView]|"
options:0
metrics:nil
views:views]];
}
- (void)scrollViewSetUp {
[self.view addSubview:self.pagingScrollView];
UIView *lastView = nil;
NSInteger arrayCount = 5;
for(NSInteger index = 0; index < arrayCount; index++)
{
UIView *view = [[UIView alloc] initWithFrame:CGRectZero];
view.translatesAutoresizingMaskIntoConstraints = NO;
view.backgroundColor = [UIColor yellowColor];
[self.pagingScrollView addSubview:view];
[self.pagingScrollView addConstraint:[NSLayoutConstraint constraintWithItem:view
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.pagingScrollView
attribute:NSLayoutAttributeTop
multiplier:1
constant:40]];
[self.pagingScrollView addConstraint:[NSLayoutConstraint constraintWithItem:view
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:self.pagingScrollView
attribute:NSLayoutAttributeHeight
multiplier:0.80
constant:0]];
[self.pagingScrollView addConstraint:[NSLayoutConstraint constraintWithItem:view
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:self.pagingScrollView
attribute:NSLayoutAttributeWidth
multiplier:0.80
constant:0]];
if (lastView == nil && index == 0){
[self.pagingScrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|-20-[view(==_pagingScrollView)]"
options:0
metrics:nil
views:#{#"view":view, #"_pagingScrollView":_pagingScrollView}]];
} else {
[self.pagingScrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:[lastView]-20-[view]"
options:0
metrics:nil
views:#{#"lastView":lastView, #"view":view, #"_pagingScrollView":_pagingScrollView}]];
}
if(index == arrayCount-1) {
[self.pagingScrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:[view]-20-|"
options:0
metrics:nil
views:#{#"view":view}]];
}
lastView = view;
}
}
#end
Any pointers/comments/feedback highly appreciated. Thanks.

Answer 1

Is this you want？
//
// ViewController.h
// Test
//
// Created by Lee on 7/8/16.
// Copyright © 2016 Lee. All rights reserved.
//
#import <UIKit/UIKit.h>
#interface ViewController : UIViewController
#property (nonatomic, strong) UIScrollView *pagingScrollView;
#end
//
// ViewController.m
// Test
//
// Created by Lee on 7/8/16.
// Copyright © 2016 Lee. All rights reserved.
//
#import "ViewController.h"
#interface ViewController ()<UIScrollViewDelegate>
#property (nonatomic,strong)NSMutableArray *subviewsCenterArray;
#end
#implementation ViewController
- (UIScrollView *)pagingScrollView {
if (!_pagingScrollView) {
_pagingScrollView = [[UIScrollView alloc] initWithFrame:CGRectZero];
_pagingScrollView.translatesAutoresizingMaskIntoConstraints = NO;
_pagingScrollView.backgroundColor = [UIColor orangeColor];
_pagingScrollView.showsHorizontalScrollIndicator = NO;
_pagingScrollView.showsVerticalScrollIndicator = NO;
_pagingScrollView.contentInset = UIEdgeInsetsZero;
_pagingScrollView.pagingEnabled = NO;
_pagingScrollView.clipsToBounds = NO;
_pagingScrollView.bounces = NO;
_pagingScrollView.delegate = self;
}
return _pagingScrollView;
}
- (void)viewDidLoad {
[super viewDidLoad];
[self scrollViewSetUp];
NSDictionary *views = NSDictionaryOfVariableBindings(_pagingScrollView);
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|[_pagingScrollView]|"
options:0
metrics:nil
views:views]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:|[_pagingScrollView]|"
options:0
metrics:nil
views:views]];
}
- (void)scrollViewSetUp {
[self.view addSubview:self.pagingScrollView];
UIView *lastView = nil;
NSInteger arrayCount = 5;
_subviewsCenterArray = [NSMutableArray array];
for(NSInteger index = 0; index < arrayCount; index++)
{
UIView *view = [[UIView alloc] initWithFrame:CGRectZero];
view.translatesAutoresizingMaskIntoConstraints = NO;
view.backgroundColor = [UIColor colorWithRed:arc4random()%255/255.0 green:arc4random()%255/255.0 blue:arc4random()%255/255.0 alpha:1];
view.tag = 9999;
view.layer.cornerRadius = 6;
[self.pagingScrollView addSubview:view];
[self.pagingScrollView addConstraint:[NSLayoutConstraint constraintWithItem:view
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.pagingScrollView
attribute:NSLayoutAttributeTop
multiplier:1
constant:40]];
[self.pagingScrollView addConstraint:[NSLayoutConstraint constraintWithItem:view
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:self.pagingScrollView
attribute:NSLayoutAttributeHeight
multiplier:0.80
constant:0]];
[self.pagingScrollView addConstraint:[NSLayoutConstraint constraintWithItem:view
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:self.pagingScrollView
attribute:NSLayoutAttributeWidth
multiplier:0.80
constant:0]];
if (lastView == nil && index == 0){
[self.pagingScrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|-20-[view(==_pagingScrollView)]"
options:0
metrics:nil
views:#{#"view":view, #"_pagingScrollView":_pagingScrollView}]];
} else {
[self.pagingScrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:[lastView]-20-[view]"
options:0
metrics:nil
views:#{#"lastView":lastView, #"view":view, #"_pagingScrollView":_pagingScrollView}]];
}
if(index == arrayCount-1) {
[self.pagingScrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:[view]-20-|"
options:0
metrics:nil
views:#{#"view":view}]];
}
[self.view layoutIfNeeded];
lastView = view;
}
}
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{
[self changeTheCardStatus:scrollView];
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
[self changeTheCardStatus:scrollView];
}
-(void)changeTheCardStatus:(UIScrollView *)scrollView{
for (UIView *view in scrollView.subviews) {
if (view.tag == 9999) {
[_subviewsCenterArray addObject:#(view.center.x)];
}
}
CGFloat currentCenterOffsetX = scrollView.contentOffset.x + CGRectGetWidth(self.view.frame)/2.0;
NSMutableArray *absoluteValueArray = [NSMutableArray array];
NSMutableDictionary *absoluteValueDictionary = [NSMutableDictionary dictionary];
for (int i = 0; i < _subviewsCenterArray.count; i ++) {
float subviewsCenterPointX = [_subviewsCenterArray[i] floatValue];
double absolute = fabs(subviewsCenterPointX - currentCenterOffsetX);
[absoluteValueArray addObject:#(absolute)];
[absoluteValueDictionary setValue:#(subviewsCenterPointX) forKey:[NSString stringWithFormat:#"%f",absolute]];
}
[absoluteValueArray sortUsingComparator:^NSComparisonResult(id _Nonnull obj1, id _Nonnull obj2) {
double a = [obj1 doubleValue];
double b = [obj2 doubleValue];
if (a>b) {
return NSOrderedDescending;
}
else if (a<b){
return NSOrderedAscending;
}
else{
return NSOrderedSame;
}
}];
double shortValue = [absoluteValueArray.firstObject doubleValue];
double centerX = [[absoluteValueDictionary objectForKey:[NSString stringWithFormat:#"%f",shortValue]] doubleValue];
[UIView animateWithDuration:0.25 animations:^{
scrollView.contentOffset = CGPointMake(centerX - CGRectGetWidth(self.view.frame)/2.0, 0);
}];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#end

Answer 2

Of course It's not. The subview of pagingScrollView doesn't have a right width! Also these subviews don's have correct horizontal margin.
First You should correct your setting width code, change the multiplier to 1 and constant to -40. Like this:
[self.pagingScrollView addConstraint:[NSLayoutConstraint constraintWithItem:view
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:self.pagingScrollView
attribute:NSLayoutAttributeWidth
multiplier:1
constant:-40]];
Then modify the subview margin, change -20 to -40, like this
[self.pagingScrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:[lastView]-40-[view]"
options:0
metrics:nil
views:#{#"lastView":lastView, #"view":view, #"_pagingScrollView":_pagingScrollView}]];