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保持缩放图像中的UIScrollView中心(Keep zoomable image in cent

2019-07-17 16:00发布

站内文章 / 后端开发
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在我的iPhone应用程序，我需要为用户提供放大/屏幕上平移一个大十岁上下的图像的能力。 这是很简单：我用UIScrollView ，设置最大/最小的比例因子和缩放/平移按预期工作。 这就是事情变得有趣。 的图像是动态的，从服务器接收。 它可以有任意尺寸。 当图像第一负载，它的按比例缩小（如果需要）以完全装配到UIScrollView和在滚动视图的中心-截图低于：

因为该图像的比例是那些滚动视图的不同，有以上，并且使得图像居中图像下方添加空白区域。 然而，当我开始缩放图像，实际图像大到足以填满整个滚动视图视口，因此在顶部/底部垫衬白色不再需要的，但是他们仍然存在，从这个截图中可以看出：

我相信这是由于事实UIImageView包含图像自动调整大小以填满整个UIScrollView和放大时，它只是按比例增长。 它具有缩放模式设置为Aspect Fit 。 UIScrollView的委托viewForZoomingInScrollView简单地返回图像视图。

我试图重新计算和重新设置UIScrollView ， contentSize和图像视图的大小scrollViewDidEndZooming方法： 

CGSize imgViewSize = imageView.frame.size;
CGSize imageSize = imageView.image.size;

CGSize realImgSize;
if(imageSize.width / imageSize.height > imgViewSize.width / imgViewSize.height) {
    realImgSize = CGSizeMake(imgViewSize.width, imgViewSize.width / imageSize.width * imageSize.height);
}
else {
    realImgSize = CGSizeMake(imgViewSize.height / imageSize.height * imageSize.width, imgViewSize.height);
}
scrollView.contentSize = realImgSize;

CGRect fr = CGRectMake(0, 0, 0, 0);
fr.size = realImgSize;
imageView.frame = fr;

然而，这只是使事情变得更糟（有界仍然存在，但平移在垂直方向上不工作）。

有没有什么办法，因为它成为不必要的自动减少空白，然后放大期间再次增加？ 我怀疑工作将需要做scrollViewDidEndZooming ，但我也不太清楚这是什么代码需要。

Answer 1:

真棒！

感谢您的代码:)

只是想我会添加到这个，我改变了它稍微改善行为。 

// make the change during scrollViewDidScroll instead of didEndScrolling...
-(void)scrollViewDidZoom:(UIScrollView *)scrollView
{
    CGSize imgViewSize = self.imageView.frame.size;
    CGSize imageSize = self.imageView.image.size;

    CGSize realImgSize;
    if(imageSize.width / imageSize.height > imgViewSize.width / imgViewSize.height) {
        realImgSize = CGSizeMake(imgViewSize.width, imgViewSize.width / imageSize.width * imageSize.height);
    }
    else {
        realImgSize = CGSizeMake(imgViewSize.height / imageSize.height * imageSize.width, imgViewSize.height);
    }

    CGRect fr = CGRectMake(0, 0, 0, 0);
    fr.size = realImgSize;
    self.imageView.frame = fr;

    CGSize scrSize = scrollView.frame.size;
    float offx = (scrSize.width > realImgSize.width ? (scrSize.width - realImgSize.width) / 2 : 0);
    float offy = (scrSize.height > realImgSize.height ? (scrSize.height - realImgSize.height) / 2 : 0);

    // don't animate the change.
    scrollView.contentInset = UIEdgeInsetsMake(offy, offx, offy, offx);
}


Answer 2:

这里是我的解决方案，可与任何标签栏或导航栏组合或W / O两种工作普遍，半透明或不。 

- (void)scrollViewDidZoom:(UIScrollView *)scrollView {
  // The scroll view has zoomed, so you need to re-center the contents
  CGSize scrollViewSize = [self scrollViewVisibleSize];
  // First assume that image center coincides with the contents box center.
  // This is correct when the image is bigger than scrollView due to zoom
  CGPoint imageCenter = CGPointMake(self.scrollView.contentSize.width/2.0,
                                    self.scrollView.contentSize.height/2.0);

  CGPoint scrollViewCenter = [self scrollViewCenter];

  //if image is smaller than the scrollView visible size - fix the image center accordingly
  if (self.scrollView.contentSize.width < scrollViewSize.width) {
    imageCenter.x = scrollViewCenter.x;
  }

  if (self.scrollView.contentSize.height < scrollViewSize.height) {
    imageCenter.y = scrollViewCenter.y;
  }

  self.imageView.center = imageCenter;
}


//return the scroll view center
- (CGPoint)scrollViewCenter {
  CGSize scrollViewSize = [self scrollViewVisibleSize];
  return CGPointMake(scrollViewSize.width/2.0, scrollViewSize.height/2.0);
}


// Return scrollview size without the area overlapping with tab and nav bar.
- (CGSize) scrollViewVisibleSize {
  UIEdgeInsets contentInset = self.scrollView.contentInset;
  CGSize scrollViewSize = CGRectStandardize(self.scrollView.bounds).size;
  CGFloat width = scrollViewSize.width - contentInset.left - contentInset.right;
  CGFloat height = scrollViewSize.height - contentInset.top - contentInset.bottom;
  return CGSizeMake(width, height);
}

为什么它比其他任何我能找到这么这么远好：

  1. 它不读取或修改图像视图的UIView的帧的性能，因为缩放图像视图具有变换应用到它。 见这里什么苹果说如何移动或当施加非恒等变换调整视图大小。

  2. 其中半透明酒吧被引入该系统启动的iOS 7会自动调整滚动视图大小，滚动内容的插图和滚动指标偏移。 因此，你不应该在你的代码修改这些为好。

FYI：用于切换这种行为在Xcode界面生成器（这是默认设置）有很复选框。 您可以在视图控制器属性找到它：

完整视图控制器的源代码被发布在这里 。

您也可以下载整个Xcode项目看到滚动视图约束，建立并通过移动最初的控制器指针到下列路径玩弄情节板中的3个不同的预设：

  1. 查看与两个半透明的标签和导航条。
  2. 查看与两个不透明的标签和导航条。
  3. 查看没有条可言。

每个选项都具有相同的VC实现正常工作。



Answer 3:

我想我得到了它。 该解决方案是使用scrollViewDidEndZooming委托的方法和在该方法中设置contentInset基于所述图像的尺寸。 下面就是该方法的样子： 

- (void)scrollViewDidEndZooming:(UIScrollView *)aScrollView withView:(UIView *)view atScale:(float)scale {
    CGSize imgViewSize = imageView.frame.size;
    CGSize imageSize = imageView.image.size;

    CGSize realImgSize;
    if(imageSize.width / imageSize.height > imgViewSize.width / imgViewSize.height) {
        realImgSize = CGSizeMake(imgViewSize.width, imgViewSize.width / imageSize.width * imageSize.height);
    }
    else {
        realImgSize = CGSizeMake(imgViewSize.height / imageSize.height * imageSize.width, imgViewSize.height);
    }

    CGRect fr = CGRectMake(0, 0, 0, 0);
    fr.size = realImgSize;
    imageView.frame = fr;

    CGSize scrSize = scrollView.frame.size;
    float offx = (scrSize.width > realImgSize.width ? (scrSize.width - realImgSize.width) / 2 : 0);
    float offy = (scrSize.height > realImgSize.height ? (scrSize.height - realImgSize.height) / 2 : 0);
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:0.25];
    scrollView.contentInset = UIEdgeInsetsMake(offy, offx, offy, offx);
    [UIView commitAnimations];
}

请注意，我使用上设置的插图动画，否则图像滚动视图内进行跳转，添加插图时。 随着动画它的幻灯片的中心。 我使用UIView beginAnimation和commitAnimation而不是动画块的，因为我需要对iPhone 3的应用程序运行。



Answer 4:

这里是SWIFT 3版本的亨克的 答案 

    func scrollViewDidZoom(_ scrollView: UIScrollView){
        let imgViewSize:CGSize! = self.imageView.frame.size;
        let imageSize:CGSize! = self.imageView.image?.size;
        var realImgSize : CGSize;
        if(imageSize.width / imageSize.height > imgViewSize.width / imgViewSize.height) {
            realImgSize = CGSize(width: imgViewSize.width,height: imgViewSize.width / imageSize.width * imageSize.height);
        }
        else {
            realImgSize = CGSize(width: imgViewSize.height / imageSize.height * imageSize.width, height: imgViewSize.height);
        }
        var fr:CGRect = CGRect.zero
        fr.size = realImgSize;
        self.imageView.frame = fr;

        let scrSize:CGSize = scrollView.frame.size;
        let offx:CGFloat = (scrSize.width > realImgSize.width ? (scrSize.width - realImgSize.width) / 2 : 0);
        let offy:CGFloat = (scrSize.height > realImgSize.height ? (scrSize.height - realImgSize.height) / 2 : 0);
        scrollView.contentInset = UIEdgeInsetsMake(offy, offx, offy, offx);

        // The scroll view has zoomed, so you need to re-center the contents
        let scrollViewSize:CGSize = self.scrollViewVisibleSize();

        // First assume that image center coincides with the contents box center.
        // This is correct when the image is bigger than scrollView due to zoom
        var imageCenter:CGPoint = CGPoint(x: self.scrollView.contentSize.width/2.0, y:
                                          self.scrollView.contentSize.height/2.0);

        let scrollViewCenter:CGPoint = self.scrollViewCenter()

        //if image is smaller than the scrollView visible size - fix the image center accordingly
        if (self.scrollView.contentSize.width < scrollViewSize.width) {
            imageCenter.x = scrollViewCenter.x;
        }

        if (self.scrollView.contentSize.height < scrollViewSize.height) {
            imageCenter.y = scrollViewCenter.y;
        }

        self.imageView.center = imageCenter;

    }
    //return the scroll view center
    func scrollViewCenter() -> CGPoint {
        let scrollViewSize:CGSize = self.scrollViewVisibleSize()
        return CGPoint(x: scrollViewSize.width/2.0, y: scrollViewSize.height/2.0);
    }
    // Return scrollview size without the area overlapping with tab and nav bar.
    func scrollViewVisibleSize() -> CGSize{

        let contentInset:UIEdgeInsets = self.scrollView.contentInset;
        let scrollViewSize:CGSize = self.scrollView.bounds.standardized.size;
        let width:CGFloat = scrollViewSize.width - contentInset.left - contentInset.right;
        let height:CGFloat = scrollViewSize.height - contentInset.top - contentInset.bottom;
        return CGSize(width:width, height:height);
    }


Answer 5:

这里是关于夫特3.1测试的延伸。 只要创建一个单独的* .swift文件并粘贴下面的代码： 

import UIKit

extension UIScrollView {

    func applyZoomToImageView() {
        guard let imageView = delegate?.viewForZooming?(in: self) as? UIImageView else { return }
        guard let image = imageView.image else { return }
        guard imageView.frame.size.valid && image.size.valid else { return }
        let size = image.size ~> imageView.frame.size
        imageView.frame.size = size
        self.contentInset = UIEdgeInsets(
            x: self.frame.size.width ~> size.width,
            y: self.frame.size.height ~> size.height
        )
        imageView.center = self.contentCenter
        if self.contentSize.width < self.visibleSize.width {
            imageView.center.x = self.visibleSize.center.x
        }
        if self.contentSize.height < self.visibleSize.height {
            imageView.center.y = self.visibleSize.center.y
        }
    }

    private var contentCenter: CGPoint {
        return CGPoint(x: contentSize.width / 2, y: contentSize.height / 2)
    }

    private var visibleSize: CGSize {
        let size: CGSize = bounds.standardized.size
        return CGSize(
            width:  size.width - contentInset.left - contentInset.right,
            height: size.height - contentInset.top - contentInset.bottom
        )
    }
}

fileprivate extension CGFloat {

    static func ~>(lhs: CGFloat, rhs: CGFloat) -> CGFloat {
        return lhs > rhs ? (lhs - rhs) / 2 : 0.0
    }
}

fileprivate extension UIEdgeInsets {

    init(x: CGFloat, y: CGFloat) {
        self.bottom = y
        self.left = x
        self.right = x
        self.top = y
    }
}

fileprivate extension CGSize {

    var valid: Bool {
        return width > 0 && height > 0
    }

    var center: CGPoint {
        return CGPoint(x: width / 2, y: height / 2)
    }

    static func ~>(lhs: CGSize, rhs: CGSize) -> CGSize {
        switch lhs > rhs {
        case true:
            return CGSize(width: rhs.width, height: rhs.width / lhs.width * lhs.height)
        default:
            return CGSize(width: rhs.height / lhs.height * lhs.width, height: rhs.height)
        }
    }

    static func >(lhs: CGSize, rhs: CGSize) -> Bool {
        return lhs.width / lhs.height > rhs.width / rhs.height
    }
}

使用方式： 

extension YOUR_SCROLL_VIEW_DELEGATE: UIScrollViewDelegate {

    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        return YOUR_IMAGE_VIEW
    }

    func scrollViewDidZoom(_ scrollView: UIScrollView){
        scrollView.applyZoomToImageView()
    }
}


文章来源: Keep zoomable image in center of UIScrollView
标签： iphone ios uiscrollview zoom image-zoom
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