Ios 如何使用contentOffset在UIScrollView中居中放置内容

这应该是一个很容易的问题，但我有困难得到想要的结果。我有宽度为320的水平滚动UIScrollView。其内容的宽度为5000。我正试图以以下内容为中心：

// 'self' is the UIScrollView
CGFloat newContentOffsetX = (self.width/2) + (self.contentSize.width/2);
self.contentOffset = CGPointMake(newContentOffsetX, 0);

我不明白为什么这不是以内容为中心。你能看出计算有什么问题吗？

我想你需要：

CGFloat newContentOffsetX = (self.contentSize.width/2) - (self.bounds.size.width/2);

图表：

|------------------------self.contentSize.width------------------------|
                         |-----self.width-----|
|-------- offset --------|
                                    ^ center

使用以下代码：

CGFloat newContentOffsetX = (scrollView.contentSize.width - scrollView.frame.size.width) / 2;
scrollView.contentOffset = CGPointMake(newContentOffsetX, 0);

---

Swift 4

滚动至滚动视图的内容中心

let centerOffsetX = (scrollView.contentSize.width - scrollView.frame.size.width) / 2
let centerOffsetY = (scrollView.contentSize.height - scrollView.frame.size.height) / 2
let centerPoint = CGPoint(x: centerOffsetX, y: centerOffsetY)
scrollView.setContentOffset(centerPoint, animated: true)

---

不是最好的解决方案，但可能对您有效

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    [self centerScrollViewAnimated:NO];
}

- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale {
    [self centerScrollViewAnimated:YES];
}

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
    *targetContentOffset = [self suggestedCenteredContentOffset];
}

- (CGPoint)suggestedCenteredContentOffset {
    CGSize imageSize = self.pickedImage.size;
    CGSize containerSize = self.zoomingScrollView.bounds.size;
    CGPoint result = self.zoomingScrollView.contentOffset;

    if ( self.zoomingScrollView.zoomScale * imageSize.width < containerSize.width )
        result.x = MIN((self.zoomingScrollView.zoomScale * imageSize.width - containerSize.width)/2, 0);

    if ( self.zoomingScrollView.zoomScale * imageSize.height < containerSize.height )
        result.y = MIN((self.zoomingScrollView.zoomScale * imageSize.height - containerSize.height)/2, 0);

    return result;
}

- (void)centerScrollViewAnimated:(BOOL)animated {
    [self.zoomingScrollView setContentOffset:[self suggestedCenteredContentOffset] animated:animated];
}

-（void）ViewDidLayoutSubView{
[超级视图布局子视图]；
[self-centerScrollViewAnimated:否]；
}
-（无效）ScrollViewDiEndZooming:（UIScrollView*）带视图的scrollView:（UIView*）按比例查看：（CGFloat）比例{
[self-centerScrollViewAnimated:是]；
}
-（void）ScrollViewWillendDraging:（UIScrollView*）带速度的scrollView:（CGPoint）速度目标内容偏移量：（inout CGPoint*）目标内容偏移量{
*targetContentOffset=[self-suggestedCenteredContentOffset]；
}
-（CGPoint）建议的中心内容偏移量{
CGSize imageSize=self.pickedImage.size；
CGSize containerSize=self.zoomingScrollView.bounds.size；
CGPoint结果=self.zoomingScrollView.contentOffset；
if（self.zoomingScrollView.zoomScale*imageSize.width

我创建了一个简单的UIScrollView扩展，它具有IBInspectable属性，可以水平和/或垂直地将内容居中。只有当scrollview内容大小小于scrollview大小时，它才起作用

以下是Swift 5.2代码：

import UIKit

@IBDesignable class CenteredScrollView: UIScrollView {
    @IBInspectable var verticallyCentered: Bool = false
    @IBInspectable var horizontallyCentered: Bool = false

    override var contentSize: CGSize {
        didSet {
            if contentSize.height <= bounds.height && verticallyCentered {
                centerVertically()
            }

            if contentSize.width <= bounds.width && horizontallyCentered {
                centerHorizontally()
            }
        }
    }

    private func centerVertically() {
        let yContentOffset = (contentSize.height / 2) - (bounds.size.height / 2)
        contentOffset = CGPoint(x: contentOffset.x, y: yContentOffset)
    }

    private func centerHorizontally() {
        let xContentOffset = (contentSize.width / 2) - (bounds.size.width / 2)
        contentOffset = CGPoint(x: xContentOffset, y: contentOffset.y)
    }
}

导入UIKit
@IBDesignable类中心滚动视图：UIScrollView{
@IBInspectable var verticallyCentered:Bool=false
@IBInspectable var HorizontallyCenter:Bool=false
覆盖变量contentSize:CGSize{
迪塞特{
如果contentSize.heightSwift 5+

@IBDesignable class CenteredScrollView: UIScrollView {
    
    @IBInspectable var isVerticallyCentered: Bool = false
    @IBInspectable var isHorizontallyCentered: Bool = false

    public func center(vertically: Bool, horizontally:Bool, animated: Bool) {
        
        guard vertically || horizontally else {
            return
        }
        
        var offset = contentOffset
        if vertically && contentSize.height <= bounds.height {
            offset.y = (contentSize.height / 2) - (bounds.size.height / 2)
        }

        if horizontally && contentSize.width <= bounds.width {
            offset.x = (contentSize.width / 2) - (bounds.size.width / 2)
        }
        setContentOffset(offset, animated: animated)
        
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        center(vertically: isVerticallyCentered, horizontally: isHorizontallyCentered, animated: false)
    }
    
}

@IBDesignable class CenteredScrollView:UIScrollView{
@IBInspectable var垂直居中：Bool=false
@IBInspectable var isHorizontallyCentered:Bool=false
公共函数中心（垂直：布尔，水平：布尔，动画：布尔）{
垂直防护| |水平防护{
返回
}
var offset=contentOffset
如果垂直（&contentSize.height），请对“self.width”表示抱歉混乱。这是我用UIView分类添加的快捷方式。为什么要使用self.bounds而不是self.frame？我怀疑
self.width
不是真正的问题，而是你想从
contentSize.width
中减去它-但我习惯性地使用了
self.bounds
。
self.bounds.size
和
self.frame.size
应该相同；我倾向于使用
self.bounds
除非我需要使用
self.frame.origin
获得的相对于superview的原点。