UiScrollview scrollviewDidScroll 检测用户触摸的滚动视图

Question

我在我的应用程序中使用了一个 UIScrollView，并使用 scrollviewDidScroll 方法来移动一些不在滚动视图内的其他视图。这种行为只应在用户实际使用手指移动滚动视图时发生，而不是触摸事件结束时发生。

目前我正在使用滚动视图的 dragging 属性来获得这种行为，但它存在一个问题：当用户在滚动视图上滑动并在它停止减速之前再次触摸它时，dragging 属性不为真，尽管用户正在用手指拖动滚动视图。

- Nils Ziehn

---

在 scrollViewDidScroll 方法中，查看你的 tableView 的 UIGestureRecognizerState，例如 yourTableView.panGestureRecognizer.state。它会告诉你用户触摸的具体状态。 - n00bProgrammer

Done. With sample code - n00bProgrammer

Answer 1

UIScrollView有一个panGestureRecogniser属性，可以跟踪滚动视图中的平移手势。您可以在scrollViewDidScroll中跟踪平移手势的state，以确切地了解平移的状态。

Swift 4.0

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    if scrollView.isEqual(yourScrollView) {
        switch scrollView.panGestureRecognizer.state {
            case .began:
                // User began dragging
                print("began")
            case .changed:
                // User is currently dragging the scroll view
                print("changed")
            case .possible:
                // The scroll view scrolling but the user is no longer touching the scrollview (table is decelerating)
                print("possible")
            default:
                break
        }
    }
}

Objective-C

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    if ([scrollView isEqual:yourScrollView]) {

        switch (scrollView.panGestureRecognizer.state) {

            case UIGestureRecognizerStateBegan:

                // User began dragging
                break;

            case UIGestureRecognizerStateChanged:

                // User is currently dragging the scroll view
                break;

            case UIGestureRecognizerStatePossible:

                // The scroll view scrolling but the user is no longer touching the scrollview (table is decelerating)
                break;

            default:
                break;
        }
    }
}

- n00bProgrammer

Answer 2

我认为更好的答案是使用UIScrollViewDelegate，它有以下通知：

// called on start of dragging (may require some time and or distance to move)
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView;
// called on finger up if the user dragged. velocity is in points/millisecond. targetContentOffset may be changed to adjust where the scroll view comes to rest
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset NS_AVAILABLE_IOS(5_0);
// called on finger up if the user dragged. decelerate is true if it will continue moving afterwards
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate;

- Marek R

---

你还需要监听 scrollViewDidScrollToTop。 - kelin

@kelin 这与用户触摸有什么关系？ - Marek R

当用户双击状态栏时，将调用此事件。这会导致表视图滚动到顶部。请在UIScrollViewDelegate文档中了解更多信息。 - kelin

这与问题有什么关系？ - Marek R

Answer 3

var lastVelocityYSign = 0

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    let currentVelocityY =  scrollView.panGestureRecognizer.velocity(in: scrollView.superview).y
    let currentVelocityYSign = Int(currentVelocityY).signum()
    if currentVelocityYSign != lastVelocityYSign &&
        currentVelocityYSign != 0 {
        lastVelocityYSign = currentVelocityYSign
    }
    if lastVelocityYSign < 0 {
        print("SCROLLING DOWN")
    } else if lastVelocityYSign > 0 {
        print("SCOLLING UP")
    }
}

Mos6y的回答： https://medium.com/@Mos6yCanSwift/swift-ios-determine-scroll-direction-d48a2327a004 （原文链接）

- alearner