在UIScrollView中查找滚动方向？

Question

我有UIScrollView只允许水平滚动，我想知道用户滚动的方向（左，右）。我所做的是继承UIScrollView并覆盖touchesMoved方法：

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    [super touchesMoved:touches withEvent:event];

    UITouch *touch = [touches anyObject];
    float now = [touch locationInView:self].x;
    float before = [touch previousLocationInView:self].x;
    NSLog(@"%f %f", before, now);
    if (now > before){
        right = NO;
        NSLog(@"LEFT");
    }
    else{
        right = YES;
        NSLog(@"RIGHT");

    }

}

但是当我移动时，这种方法有时根本不会被调用。你觉得怎么样？

Answer 1

确定方向相当简单，但请记住，方向可以在手势过程中多次改变。例如，如果您有一个打开分页的滚动视图，并且用户滑动以转到下一页，则初始方向可能是向右的，但如果您打开了弹跳，它将暂时完全没有方向然后简单地向左走。

要确定方向，您需要使用UIScrollView scrollViewDidScroll委托。在此示例中，我创建了一个名为lastContentOffset的变量，用于将当前内容偏移量与前一个内容进行比较。如果它更大，则scrollView向右滚动。如果它小于那么scrollView向左滚动：

// somewhere in the private class extension
@property (nonatomic, assign) CGFloat lastContentOffset;

// somewhere in the class implementation
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    ScrollDirection scrollDirection;

    if (self.lastContentOffset > scrollView.contentOffset.x) {
        scrollDirection = ScrollDirectionRight;
    } else if (self.lastContentOffset < scrollView.contentOffset.x) {
        scrollDirection = ScrollDirectionLeft;
    }

    self.lastContentOffset = scrollView.contentOffset.x;

    // do whatever you need to with scrollDirection here.    
}

我正在使用以下枚举来定义方向。将第一个值设置为ScrollDirectionNone具有额外的好处，即在初始化变量时将该方向设置为默认值：

typedef NS_ENUM(NSInteger, ScrollDirection) {
    ScrollDirectionNone,
    ScrollDirectionRight,
    ScrollDirectionLeft,
    ScrollDirectionUp,
    ScrollDirectionDown,
    ScrollDirectionCrazy,
};

Answer 2

  

...我想知道用户滚动的方向（左，右）。

在这种情况下，在iOS 5及更高版本上，使用UIScrollViewDelegate确定用户平移手势的方向：

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{ 
    if ([scrollView.panGestureRecognizer translationInView:scrollView.superview].x > 0) {
        // handle dragging to the right
    } else {
        // handle dragging to the left
    }
}

Answer 3

使用scrollViewDidScroll:是查找当前方向的好方法。

如果您想知道用户完成滚动后 之后的方向，请使用以下内容：

@property (nonatomic) CGFloat lastContentOffset;

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

    self.lastContentOffset = scrollView.contentOffset.x;
}

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

    if (self.lastContentOffset < scrollView.contentOffset.x) {
        // moved right
    } else if (self.lastContentOffset > scrollView.contentOffset.x) {
        // moved left
    } else {
        // didn't move
    }
}

Answer 4

无需添加额外的变量来跟踪此情况。只需使用此UIScrollView的{​​{1}}属性即可。不幸的是，这仅在速度不为0时才有效：

panGestureRecognizer

您可以使用x和y组件的组合来检测上，下，左和右。

Answer 5

解决方案

func scrollViewDidScroll(scrollView: UIScrollView) {
     if(scrollView.panGestureRecognizer.translationInView(scrollView.superview).y > 0)
     {
         print("up")
     }
    else
    {
         print("down")
    } 
}

Answer 6

在iOS8 Swift中我使用了这种方法：

override func scrollViewDidScroll(scrollView: UIScrollView){

    var frame: CGRect = self.photoButton.frame
    var currentLocation = scrollView.contentOffset.y

    if frame.origin.y > currentLocation{
        println("Going up!")
    }else if frame.origin.y < currentLocation{
        println("Going down!")
    }

    frame.origin.y = scrollView.contentOffset.y + scrollHeight
    photoButton.frame = frame
    view.bringSubviewToFront(photoButton)

}

我有一个动态视图，当用户滚动时会改变位置，因此视图看起来像是停留在屏幕上的相同位置。我也在跟踪用户上升或下降的时间。

这也是另一种方式：

func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    if targetContentOffset.memory.y < scrollView.contentOffset.y {
        println("Going up!")
    } else {
        println("Going down!")
    }
}

Answer 7

Swift 4：

对于水平滚动，您只需执行以下操作：

if scrollView.panGestureRecognizer.translation(in: scrollView.superview).x > 0 {
   print("left")
} else {
   print("right")
}

使用.x

进行垂直滚动更改.y

Answer 8

这对我有用（在Objective-C中）：

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

        NSString *direction = ([scrollView.panGestureRecognizer translationInView:scrollView.superview].y >0)?@"up":@"down";
        NSLog(@"%@",direction);
    }

Answer 9

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {

    CGPoint targetPoint = *targetContentOffset;
    CGPoint currentPoint = scrollView.contentOffset;

    if (targetPoint.y > currentPoint.y) {
        NSLog(@"up");
    }
    else {
        NSLog(@"down");
    }
}

Answer 10

或者，可以观察关键路径“contentOffset”。当您无法设置/更改滚动视图的委托时，这非常有用。

[yourScrollView addObserver:self forKeyPath:@"contentOffset" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];

添加观察者后，您现在可以：

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
    CGFloat newOffset = [[change objectForKey:@"new"] CGPointValue].y;
    CGFloat oldOffset = [[change objectForKey:@"old"] CGPointValue].y;
    CGFloat diff = newOffset - oldOffset;
    if (diff < 0 ) { //scrolling down
        // do something
    }
}

请记得在需要时移除观察者。例如您可以在 viewWillAppear 中添加观察者，并在 viewWillDisappear

中将其删除

Answer 11

在swift：

    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
    if scrollView.panGestureRecognizer.translation(in: scrollView).y < 0 {
        print("down")
    } else {
        print("up")
    }
}

您也可以在scrollViewDidScroll中执行此操作。

Answer 12

Here is my solution for behavior like in @followben answer, but without loss with slow start (when dy is 0)

@property (assign, nonatomic) BOOL isFinding;
@property (assign, nonatomic) CGFloat previousOffset;

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
    self.isFinding = YES;
}
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if (self.isFinding) {
        if (self.previousOffset == 0) {
            self.previousOffset = self.tableView.contentOffset.y;

        } else {
            CGFloat diff = self.tableView.contentOffset.y - self.previousOffset;
            if (diff != 0) {
                self.previousOffset = 0;
                self.isFinding = NO;

                if (diff > 0) {
                    // moved up
                } else {
                    // moved down
                }
            }
        }
    }
}

Answer 13

斯威夫特 5

使用 enum 进行垂直滚动的更干净的解决方案。

enum ScrollDirection {
    case up, down
}

var scrollDirection: ScrollDirection? {
    let yTranslation = scrollView.panGestureRecognizer.translation(in: scrollView.superview).y

    if yTranslation > 0 {
        return .up
    } else if yTranslation < 0 {
        return .down
    } else {
        return nil
    }
}

用法

switch scrollDirection {
case .up:   print("up")
case .down: print("down")
default:    print("no scroll")
}

Answer 14

//Vertical detection

    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")
                }
            }

来自Mos6y的答案 https://medium.com/@Mos6yCanSwift/swift-ios-determine-scroll-direction-d48a2327a004

Answer 15

我更愿意根据@memmons的答案进行过滤

在Objective-C中：

// in the private class extension
@property (nonatomic, assign) CGFloat lastContentOffset;

// in the class implementation
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    if (fabs(self.lastContentOffset - scrollView.contentOffset.x) > 20 ) {
        self.lastContentOffset = scrollView.contentOffset.x;
    }

    if (self.lastContentOffset > scrollView.contentOffset.x) {
        //  Scroll Direction Left
        //  do what you need to with scrollDirection here.
    } else {
        //  omitted 
        //  if (self.lastContentOffset < scrollView.contentOffset.x)

        //  do what you need to with scrollDirection here.
        //  Scroll Direction Right
    } 
}

在- (void)scrollViewDidScroll:(UIScrollView *)scrollView中进行测试时：

NSLog(@"lastContentOffset: --- %f,   scrollView.contentOffset.x : --- %f", self.lastContentOffset, scrollView.contentOffset.x);

self.lastContentOffset变化非常快，值差接近0.5f。

没有必要。

有时，在正确的条件下进行操作时，您的方向可能会迷路。 （有时会跳过实现语句）

例如：

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

    CGFloat viewWidth = scrollView.frame.size.width;

    self.lastContentOffset = scrollView.contentOffset.x;
    // Bad example , needs value filtering

    NSInteger page = scrollView.contentOffset.x / viewWidth;

    if (page == self.images.count + 1 && self.lastContentOffset < scrollView.contentOffset.x ){
          //  Scroll Direction Right
          //  do what you need to with scrollDirection here.
    }
   ....

在Swift 4中：

var lastContentOffset: CGFloat = 0

func scrollViewDidScroll(_ scrollView: UIScrollView) {

     if (abs(lastContentOffset - scrollView.contentOffset.x) > 20 ) {
         lastContentOffset = scrollView.contentOffset.x;
     }

     if (lastContentOffset > scrollView.contentOffset.x) {
          //  Scroll Direction Left
          //  do what you need to with scrollDirection here.
     } else {
         //  omitted
         //  if (self.lastContentOffset < scrollView.contentOffset.x)

         //  do what you need to with scrollDirection here.
         //  Scroll Direction Right
    }
}

Answer 16

我检查了一些答案，并通过将所有内容包装在UIScrollView类别的下拉列表中详细阐述了AnswerBot的答案。 “lastContentOffset”保存在uiscrollview中，然后只需要调用它：

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
  [scrollView setLastContentOffset:scrollView.contentOffset];
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
  if (scrollView.scrollDirectionX == ScrollDirectionRight) {
    //Do something with your views etc
  }
  if (scrollView.scrollDirectionY == ScrollDirectionUp) {
    //Do something with your views etc
  }
}

源代码 https://github.com/tehjord/UIScrollViewScrollingDirection

Answer 17

如果您使用UIScrollView和UIPageControl，此方法也将更改PageControl的页面视图。

  func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {

    let targetOffset = targetContentOffset.memory.x
    let widthPerPage = scrollView.contentSize.width / CGFloat(pageControl.numberOfPages)

    let currentPage = targetOffset / widthPerPage
    pageControl.currentPage = Int(currentPage)
}

感谢@Esq的Swift代码。

Answer 18

Swift 2.2 简单解决方案 ，可以毫无损失地跟踪 单个和多个方向 。

  // Keep last location with parameter
  var lastLocation:CGPoint = CGPointZero

  // We are using only this function so, we can
  // track each scroll without lose anyone
  override func scrollViewWillBeginDragging(scrollView: UIScrollView) {
    let currentLocation = scrollView.contentOffset

    // Add each direction string
    var directionList:[String] = []

    if lastLocation.x < currentLocation.x {
      //print("right")
      directionList.append("Right")
    } else if lastLocation.x > currentLocation.x {
      //print("left")
      directionList.append("Left")
    }

    // there is no "else if" to track both vertical
    // and horizontal direction
    if lastLocation.y < currentLocation.y {
      //print("up")
      directionList.append("Up")
    } else if lastLocation.y > currentLocation.y {
      //print("down")
      directionList.append("Down")
    }

    // scrolled to single direction
    if directionList.count == 1 {
      print("scrolled to \(directionList[0]) direction.")
    } else if directionList.count > 0  { // scrolled to multiple direction
      print("scrolled to \(directionList[0])-\(directionList[1]) direction.")
    }

    // Update last location after check current otherwise,
    // values will be same
    lastLocation = scrollView.contentOffset
  }

Answer 19

简短＆amp;很容易，只需检查速度值，如果它大于零，那么它向左滚动就是右边：

func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {

    var targetOffset = Float(targetContentOffset.memory.x)
    println("TargetOffset: \(targetOffset)")
    println(velocity)

    if velocity.x < 0 {
        scrollDirection = -1 //scrolling left
    } else {
        scrollDirection = 1 //scrolling right
    }
}

Answer 20

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
NSLog(@"px %f py %f",velocity.x,velocity.y);}

使用scrollview的委托方法。

如果y坐标速度为+ ve滚动视图向下滚动，如果是-ve scrollview向上滚动。 类似地，可以使用x坐标检测左右滚动。

Answer 21

好的，对我来说，这个实现工作真的很好：

@property (nonatomic, assign) CGPoint lastContentOffset;


- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
    _lastContentOffset.x = scrollView.contentOffset.x;
    _lastContentOffset.y = scrollView.contentOffset.y;

}


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

    if (_lastContentOffset.x < (int)scrollView.contentOffset.x) {
        // moved right
        NSLog(@"right");
    }
    else if (_lastContentOffset.x > (int)scrollView.contentOffset.x) {
        // moved left
        NSLog(@"left");

    }else if (_lastContentOffset.y<(int)scrollView.contentOffset.y){
        NSLog(@"up");

    }else if (_lastContentOffset.y>(int)scrollView.contentOffset.y){
        NSLog(@"down");
        [self.txtText resignFirstResponder];

    }
}

因此，这会在拖动结束后触发textView以消除

Answer 22

代码我解释自己。 CGFloat difference1和difference2在同一个类私有接口中声明。 如果contentSize保持不变，那就太好了。

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

        CGFloat contentOffSet = scrollView.contentOffset.y;
        CGFloat contentHeight = scrollView.contentSize.height;

        difference1 = contentHeight - contentOffSet;

        if (difference1 > difference2) {
            NSLog(@"Up");
        }else{
            NSLog(@"Down");
        }

        difference2 = contentHeight - contentOffSet;

       }

Answer 23

在所有上面的答案中，解决问题的两种主要方法是使用panGestureRecognizer或contentOffset。两种方法都有其优点和缺点。

方法1：panGestureRecognizer

在使用panGestureRecognizer时，如@followben所建议的那样，如果您不想以编程方式滚动滚动视图，则它可以正常工作。

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{ 
    if ([scrollView.panGestureRecognizer translationInView:scrollView.superview].x > 0) {
        // handle dragging to the right
    } else {
        // handle dragging to the left
    }
}

缺点

但是，如果使用以下代码移动滚动视图，则上层代码将无法识别它：

setContentOffset(CGPoint(x: 100, y: 0), animation: false)

方法2：contentOffset

var lastContentOffset: CGPoint = CGPoint.zero

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    if (self.lastContentOffset.x > scrollView.contentOffset.x) {
        // scroll to right
    } else if self.lastContentOffset.x < scrollView.contentOffset.x {
        // scroll to left
    }
    self.lastContentOffset = self.scrollView.contentOffset
}

缺点

如果要以编程方式在滚动过程中更改contentOffset（例如，要创建无限滚动），则此方法会出现问题，因为您可能会在更改内容视图位置时更改contentOffset，而此时需要更改上方代码跳转到向右或向左滚动。

Answer 24

打开分页时，您可以使用这些代码。

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    self.lastPage = self.currentPage;
    CGFloat pageWidth = _mainScrollView.frame.size.width;
    self.currentPage = floor((_mainScrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
    if (self.lastPage < self.currentPage) {
        //go right
        NSLog(@"right");
    }else if(self.lastPage > self.currentPage){
        //go left
        NSLog(@"left");
    }else if (self.lastPage == self.currentPage){
        //same page
        NSLog(@"same page");
    }
}