Question

我正在构建一个IOS应用程序，当您第一次开始使用该应用程序时，该应用程序以UIPageViewController开始。我一直在寻找一种淡入imageView的方法，具体取决于用户刷到下一个屏幕的距离。即：当他们刷过屏幕的一半时，alpha = 0.5，当屏幕被完全刷过时，alpha = 1.0？

我尝试使用＆＃39; animateWithDuration＆＃39;但这似乎等到视图完全在屏幕上，所以它显示了一个滞后的淡入。我想到使用gestureRecognizers，但pageViewController已经有它们，因此我将不得不重写它们。

Answer 1

在视图上添加平移手势，以了解在屏幕上刷了多少。定义一个变量说CGFloat xpostion;

- (void)panRecognized:(UIPanGestureRecognizer *)gesture { CGPoint translate = [gesture translationInView:self.view]; if (gesture.state == UIGestureRecognizerStateBegan) { xpostion = translate.x; } else if (gesture.state == UIGestureRecognizerStateEnded) { CGFloat totalXSwipe = translate.x - xpostion; CGFloat width = [UIScreen mainScreen].bounds.size.width; CGFloat percentage = fabs(totalXSwipe)/width; NSLog(@"Swipe percentage %f",percentage); //Can use in your requirement to set as alpha value as it will be always less or equal to zero } }

Answer 2

将Paresh的Objective-C代码转换为Swift：

var xpostion: CGFloat = 0.0
func panRecognized(_ gesture: UIPanGestureRecognizer?) {
    guard let translate: CGPoint? = gesture?.translation(in: view) else { return }

    if gesture?.state == .began {
        xpostion = (translate?.x)!
    } else if gesture?.state == .ended {
        let totalXSwipe: CGFloat = (translate?.x ?? 0.0) - xpostion

        let width: CGFloat = UIScreen.main.bounds.size.width

        let percentage = CGFloat(fabs(Float(totalXSwipe))) / width
        print("Swipe percentage \(percentage)")

        //Can use in your requirement to set as alpha value as it will be always less or equal to zero
    }
}

编码愉快！

Answer 3

您还可以简单地利用UIScrollView API来帮助您实现已查看/滚动的UIView的百分比。这是一个想法。

拖动UIScrollView对象并将其正确连接到Storyboard中的相应场景上，或者在代码中正确实例化，继续使当前对应的ViewController类与要计算到 UIScrollViewDelegate的屏幕百分比一致协议。

例如class YourCustomViewController: UIViewController, UIScrollViewDelegate {}

然后，在YourCustomViewController类中的某个位置，您可以实现以下代码。这是实现屏幕垂直滚动百分比的代码：

func computePercentage(in scrollView: UIScrollView) {
    let height = scrollView.contentSize.height
    let viewed = scrollView.contentOffset.y + scrollView.bounds.size.height
    let pagePercentScrolled = viewed / height * 100.0
   // print("Percent Scrolled: \(pagePercentScrolled)")

    if pagePercentScrolled >= 50.0 && pagePercentScrolled < 100.0 {
        //Do something.
        //Example, set imageView alpha to half
        yourCustomImageView.alpha = 0.5
    } else if pagePercentScrolled == 100 {
        //Do something.
        //Example, fade in/show full imageView
        yourCustomImageView.alpha = 1.0
    }
}

以相同的方式，您可以稍作更改以计算水平滚动屏幕的百分比：

    func computePercentage(in scrollView: UIScrollView) {
    let width = scrollView.contentSize.width
    let viewed = scrollView.bounds.size.width - scrollView.contentOffset.x
    let pagePercentScrolled = viewed / width * 100.0
    //print("Percent Scrolled: \(pagePercentScrolled)")

    if pagePercentScrolled >= 50.0 && pagePercentScrolled < 100.0 {
        //Do something.
        //Example, set imageView alpha to half
        yourCustomImageView.alpha = 0.5
    } else if pagePercentScrolled == 100 {
        //Do something.
        //Example, fade in/show full imageView
        yourCustomImageView.alpha = 1.0
    }
}

当然，您可以将上述两种方法简单地组合为一个。但是为了简单起见，我将它们分开。然后，您可以在YourCustomViewController上实现UIScrollViewDelegate方法，如下所示：

    // MARK: Scroll View Delegate
func scrollViewDidScroll(_ scrollView: UIScrollView) {
    computePercentage(in: scrollView)
}

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    computePercentage(in: scrollView)
}

func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
    computePercentage(in: scrollView)
}

func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    computePercentage(in: scrollView)
}

如何获得UIview在屏幕上的百分比

3 个答案: