如何在异步加载内容时设置UIScrollView contensize

Question

我的视图层次结构就是这样

PhotoDetailViewController.swift

    View
      UIScrollView
        UIImageView

我使用storyboard设置它,并向UIScrollView添加四个约束(top = 0,bottom = 0,leading = 0,tailing = 0),四个约束(top = 0,bottom = 0,leading = 0,tailing = 0)到UIImageView,但有两个错误说

"ScrollView has ambiguous scrollable content width"
"ScrollView has ambiguous scrollable content height"

我知道这是因为我没有设置UIScrollView contentSize,但我想要做的是异步加载PHAsset中的照片,所以我只能在运行时获取照片大小.所以问题是:

1:鉴于照片大小只能在运行时获取,如何解决"模糊可滚动内容"错误？

2:我应该在哪个View的生命周期方法中调用PHImageManager.requestImageForAsset？因为我认为我应该以编程方式设置UIScrollView contentSize,但什么时候？

使用PhotoDetailViewController.swift进行更新

import UIKit
import Photos

class PhotoDetailViewController : UIViewController {

@IBOutlet weak var scrollView: UIScrollView!
@IBOutlet weak var imageViewBottomConstraint: NSLayoutConstraint!
@IBOutlet weak var imageViewLeadingConstraint: NSLayoutConstraint!
@IBOutlet weak var imageViewTopConstraint: NSLayoutConstraint!
@IBOutlet weak var imageViewTrailingConstraint: NSLayoutConstraint!

var devicePhotosAsset : PHFetchResult!
var index = 0
var photo : UIImage!
var imgManager:PHImageManager!

@IBOutlet weak var imageView : UIImageView!

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)
}

override func awakeFromNib() {
    self.imgManager = PHImageManager()
}

override func viewDidLoad() {
    super.viewDidLoad()
    self.displayPhoto()
}

override func viewWillLayoutSubviews() {
    super.viewDidLayoutSubviews()
    updateMinZoomScaleForSize()
    updateConstraintsForSize()
}

func displayPhoto () {
    _ = self.imgManager.requestImageForAsset(self.devicePhotosAsset[self.index] as! PHAsset, targetSize: PHImageManagerMaximumSize, contentMode: .AspectFit, options: nil, resultHandler: {(result, info) -> Void in
            NSOperationQueue.mainQueue().addOperationWithBlock(){
                self.imageView.image = result
            }

        })
}

private func targetSize() -> CGSize {
    let scale = UIScreen.mainScreen().scale
    let targetSize = CGSizeMake(CGRectGetWidth(self.imageView.bounds)*scale, CGRectGetHeight(self.imageView.bounds)*scale)

    return targetSize
}

private func updateMinZoomScaleForSize() {
    let size = scrollView.bounds.size
    let widthScale = size.width / imageView.bounds.width
    let heightScale = size.height / imageView.bounds.height
    let minScale = min(widthScale, heightScale)

    scrollView.minimumZoomScale = minScale

    scrollView.zoomScale = minScale
}

func recenterImage(){
    let scrollViewSize = scrollView.bounds.size
    let imageSize = imageView.frame.size

    let horizontalSpace = imageSize.width < scrollViewSize.width ? (scrollViewSize.width - imageSize.width)/2 : 0
    let verticalSpace = imageSize.height < scrollViewSize.height ? (scrollViewSize.height - imageSize.height)/2 : 0
    scrollView.contentInset = UIEdgeInsets(top: verticalSpace, left: horizontalSpace, bottom: verticalSpace, right: horizontalSpace)
}

private func updateConstraintsForSize() {
    let size = scrollView.bounds.size
    let yOffset = max(0, (size.height - imageView.frame.height) / 2)
    imageViewTopConstraint.constant = yOffset
    imageViewBottomConstraint.constant = yOffset

    let xOffset = max(0, (size.width - imageView.frame.width) / 2)
    imageViewLeadingConstraint.constant = xOffset
    imageViewTrailingConstraint.constant = xOffset

    view.layoutIfNeeded()
}
}

extension PhotoDetailViewController: UIScrollViewDelegate {
func viewForZoomingInScrollView(scrollView: UIScrollView) -> UIView? {
    return imageView
}

func scrollViewDidZoom(scrollView: UIScrollView) {
    updateConstraintsForSize()
}
}

Answer 1

您现有的约束足以设置内容大小,它只是基于图像视图的内在内容大小,并且在图像视图具有图像之前不存在.

您可以使用默认值向图像视图添加宽度和高度约束,并在将图像设置为视图时停用这些约束.或者您可以使用占位符图像并避免这些额外的约束,因为您始终具有图像视图的内在内容大小.

Answer 2

获取数据后，只需添加这些行

float sizeOfContent = 0;
UIView *lLast = [yourscrollview.subviews lastObject];
NSInteger wd = lLast.frame.origin.y;
NSInteger ht = lLast.frame.size.height;
sizeOfContent = wd+ht;
yourscrollview.contentSize = CGSizeMake(yourscrollview.frame.size.width, sizeOfContent);

希望这可以帮助