App crashes when UIScrollView touched

Question

I have a RootViewController which creates a SecondViewController. Inside the SecondViewController in viewDidAppear, I create a UIScrollView and a UIPageControl and add them to the view. I also do this: scrollview.delegate = self. The SecondViewController is a <UIScrollViewDelegate>. I have also implemented scrollViewDidScroll inside the SecondViewController. All of this works, compiles and runs. However, when I touch the UIScrollView, the app crashes. For the life of me, I cannot figure out why. It is the stupidest problem, but I cannot solve it.

It is very similar to this problem: UIScrollView EXC_BAD_ACCESS crash in iOS However, I tried those solutions and none of them work.

I have pasted some code below. I really appreciate the help.

RootViewController:

- (void)viewDidAppear:(BOOL)animated
{
    SecondViewController *secondViewController = [[SecondViewController alloc] init];
    secondViewController.view.frame = CGRectMake(50, 50, 925, 600);
    secondViewController.view.backgroundColor = [UIColor lightGrayColor];

    [self.view addSubview:secondViewController.view];
}

SecondViewController:

- (void)viewDidAppear:(BOOL)animated
{
    CGRect scrollViewFrame = CGRectMake(50, 50, 824, 500);
    self.scrollView = [[UIScrollView alloc] initWithFrame:scrollViewFrame];
    self.scrollView.delegate = self;
    self.scrollView.contentSize = CGSizeMake(self.scrollView.frame.size.width*3,
                                             self.scrollView.frame.size.height);
    self.scrollView.backgroundColor = [UIColor darkGrayColor];
    self.scrollView.showsHorizontalScrollIndicator = YES;
    self.scrollView.showsVerticalScrollIndicator = YES;
    self.scrollView.pagingEnabled = YES;

    [self.view addSubview:self.scrollView];

    CGRect pageControlFrame = CGRectMake(0, 0, 50, 20);
    self.pageControl = [[UIPageControl alloc] initWithFrame:pageControlFrame];
    self.pageControl.numberOfPages = 3;
    self.pageControl.currentPage = 0;
    self.pageControl.backgroundColor = [UIColor grayColor];

    [self.view addSubview:self.pageControl];
}

- (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;
}

I think the crash is due to the unexpected value in any of the variables in your "- (void)scrollViewDidScroll:(UIScrollView *)scrollView" method. So log the values of pageWidth, fractionalPage and page to check whether it gives the expected result. — Neenu, Sep 27 '13 at 04:26

score 1 · Accepted Answer · answered Sep 27 '13 at 04:25

1

your secondViewController object is deallocated as it is not retained anywhere only its view is retained as it is added as subview. You also need to retain secondViewController's object.

answered Sep 27 '13 at 04:25

Saurabh Passolia

8,099
1
26
41

Can you speak more on that? I am new to the whole retain/release thing. – tentmaking Sep 27 '13 at 04:38
1

long story short, if you're using ARC just put this in your .h file `SecondViewController *secondViewController` and use `secondViewController = [[SecondViewController alloc] init];` – Saurabh Passolia Sep 27 '13 at 06:52

App crashes when UIScrollView touched

1 Answers1