UIScrollView scroll functionality not working? - ios

Question

I am a newbie to IOS app development. I am trying to implement a scrollview. I am not able to scroll at all.
Below is my view implementation.
I created a scroll view and added small blocks with different colors in it.
I added one block out of current screen bounds so that I can scroll down the UIScrollView and view it.
#implementation CustomView
- (instancetype)init
{
self = [super init];
if (self) {
CGRect screenRect = CGRectMake(70, 100, 250, 800);
UIScrollView *scrollView = [[UIScrollView alloc] initWithFrame:screenRect];
scrollView.scrollEnabled = YES;
[scrollView setBackgroundColor:[UIColor yellowColor]];
[scrollView setAlpha:0.2];
[self addSubview:scrollView];
CGRect temp = CGRectMake(100, 150, 10, 10);
UIView *firstView = [[UIView alloc] initWithFrame:temp];
[firstView setBackgroundColor:[UIColor redColor]];
[scrollView addSubview:firstView];
temp = CGRectMake(150, 200, 10, 10);
UIView *secondView = [[UIView alloc] initWithFrame:temp];
[secondView setBackgroundColor:[UIColor greenColor]];
[scrollView addSubview:secondView];
temp = CGRectMake(200, 750, 10, 10);
UIView *thirdView = [[UIView alloc] initWithFrame:temp];
[thirdView setBackgroundColor:[UIColor orangeColor]];
[scrollView addSubview:thirdView];
scrollView.contentSize = screenRect.size;
}
return self;
}
#end
I am using the view I created before in my view controller. I am adding it to my view controller's view.
#interface ViewController ()
#property (nonatomic, readonly) CustomView *currentView;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
_currentView = [[CustomView alloc] init];
[self.view addSubview:_currentView];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#end
I am not able to scroll at all with this implementation. am i missing something ?
Can someone please explain what is wrong with my code.
Thank you

Answer 1

When you add a scrollview to the screen it should be the size which you want to display on the screen. It will be displayed on the screen simply as an UIView only when you look at it.
UIScrollView *scrollView = [[UIScrollView alloc] initWithFrame: CGRectMake(20, 20, 250, 250)];
The above initialisation will give you a scroll view of the size 250X250 placed at the position (20,20).
For scrolling you need to define the content size of the scroll view.
This content size should be bigger than your scrollview size otherwise you will not be able to differentiate it. The size of the contentsize should be decided based on the content you are going to put inside it.
For example if the three views you are adding inside the scrollview occupy a total width of 500 and a height of 300 then your content size should be equal to that only.
[scrollView setContentSize:CGSizeMake(500, 300)];
This will allow you to scroll inside the scrollview.
Also the content you are adding to you scrollview should be added considering the top left corner of the scrollView as the (0,0) location.
So if you want to display something on the top left corner of your scrollView then the frame dimensions of that particular view should be like this
CGRectMake(0,0,30,30);
This will add a view of the size 30X30 on the top left corner of the scrollView.
Hope it helps.

Answer 2

Your scroll view doesn't scroll because its frame is as large as its content size. Add this line in the view controller after before adding the scrollview as subview:
_currentView.frame = self.view.bounds ;

Answer 3

The contentSize property should not be the size of the screen, it needs to be larger if you want scrolling to work. You should calculate the size of the content within the scrollView, for example the combined height of all the subviews and the spaces between them or maybe the MaxY of the bottom view.
Also, try using a UITableView (or a UIStackView in iOS 9) to accomplish the same behavior without doing any math

Answer 4

First of all, what you are trying to do should be done using UITableView. I am not sure why are you trying to do it this way.
Anyhow, did you try to set also the contentSize property of UIScrollView?
https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIScrollView_Class/#//apple_ref/occ/instp/UIScrollView/contentSize