为什么滚动视图为零？

Question

我有以下代码：

extension SegmentedControlViewController: UIScrollViewDelegate {
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        // this checks for whether contentOffset.x is around 10 (contented shifted to the right by 10 points)
        if abs(scrollView.contentOffset.x - 10) < 1 {
            print("works")
        }
    }
}

  @IBOutlet weak var scrollView: UIScrollView!

然后我像这样调用 viewDidLoad 中的函数：

scrollViewDidScroll(scrollView)

尽管我总是收到错误消息

Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value

我做错了什么，如何让滚动视图不为零。

Answer 1

在viewDidLoad()中分配滚动视图的.delegate并开始滚动：

class SegmentedControlViewController: UIViewController {

    @IBOutlet weak var scrollView: UIScrollView!

    override func viewDidLoad() {
        super.viewDidLoad()

        // assign the delegate      
        scrollView.delegate = self
        
    }

}

extension SegmentedControlViewController: UIScrollViewDelegate {
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        // this checks for whether contentOffset.x is around 10 (contented shifted to the right by 10 points)
        if abs(scrollView.contentOffset.x - 10) < 1 {
            print("works")
        }
    }
}

编辑

如果要检查滚动视图内容是否已向右拖动超过 10 点，请使用：

extension SegmentedControlViewController: UIScrollViewDelegate {
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        // this checks for whether contentOffset.x is around 10 (contented shifted to the right by 10 points)
        if scrollView.contentOffset.x < 10 {
            print("scroll content has been dragged to the right more than 10 points")
        }
    }
}

为什么滚动视图为零？

Why is the scroll view being nil?

null

xcode

uiscrollview

swift