Question

我有一个应用程序，它通过单击按钮从服务器下载图像。图像下载后，我创建一个新的imageView并将其添加到我的contentView（UIView）。我需要创建约束 - 每个新的imageview都需要前一个约束

func addNewImageToTheScrollView(img: UIImage?) {
    if let imageResponse = img {
        let imageView = UIImageView(image: imageResponse.crop(rect: CGRect(x: 0, y: imageResponse.size.height/2, width: self.contentView.frame.width, height: 200)))
        self.contentView.addSubview(imageView)

        imageView.translatesAutoresizingMaskIntoConstraints = false
        let x = NSLayoutConstraint(item: imageView, attribute: .centerX, relatedBy: .equal, toItem: self.contentView, attribute: .centerX, multiplier: 1.0, constant: 0)
        let y = NSLayoutConstraint(item: imageView, attribute: .top, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 30)
        let width = NSLayoutConstraint(item: imageView, attribute: .width, relatedBy: .equal, toItem: self.contentView, attribute: .width, multiplier: 1.0, constant: 0)
        let height = NSLayoutConstraint(item: imageView, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 150)

        self.contentView.addConstraints([x, y])
        imageView.addConstraints([width, height])
    }
}

如果我评论约束代码，它将正常工作，除非每个新的imageView将位于视图顶部的同一位置。现在使用此约束代码，我在下载后会遇到此类代码问题

2017-07-02 14:50:01.018 ImageFromServerTest [11516：1080948] ***由于未捕获的异常终止应用程序＆＃39; NSInvalidArgumentException＆＃39;，原因：＆＃39; NSLayoutConstraint for＆gt;：乘数0或零第二项与第一属性的位置一起创建等于常数的位置的非法约束。必须成对指定位置属性。＆＃39;

Answer 1

每当使用scrollViews时，都有2个拇指规则： -

为superview提供scrollView前导，尾随，底部和顶部约束，即@IbOutlet weak var scrollView: UIScrollView! let leading = NSLayoutConstraint(item: scrollView, attribute: .leading, relatedBy: .equal, toItem: self.view, attribute: .leadingMargin, multiplier: 1.0, constant: 0) let trailing = NSLayoutConstraint(item: scrollView, attribute: .trailing, relatedBy: .equal, toItem: self.view, attribute: .trailingMargin, multiplier: 1.0, constant: 0) let top = NSLayoutConstraint(item: scrollView, attribute: .top, relatedBy: .equal, toItem: self.view, attribute: .top, multiplier: 1.0, constant: 0) let bottom = NSLayoutConstraint(item: scrollView, attribute: .bottom, relatedBy: .equal, toItem: self.view, attribute: .bottom, multiplier: 1.0, constant: 0)
```
@IbOutlet weak var contentView: UIView!

 let leading = NSLayoutConstraint(item: contentView, attribute: .leading, relatedBy: .equal, toItem: scrollView, attribute: .leading, multiplier: 1.0, constant: 0)
 let trailing = NSLayoutConstraint(item: contentView, attribute: .trailing, relatedBy: .equal, toItem: scrollView, attribute: .trailing, multiplier: 1.0, constant: 0)

 let top = NSLayoutConstraint(item: contentView, attribute: .top, relatedBy: .equal, toItem: scrollView, attribute: .top, multiplier: 1.0, constant: 0)

  //increase the constant according to how much long you need the scrollview to be
 let bottom = NSLayoutConstraint(item: contentView, attribute: .bottom, relatedBy: .equal, toItem: scrollView, attribute: .bottom, multiplier: 1.0, constant: 0) 
```

相对于scrollView

向contentView添加约束

var imageViews = [UIImageViews]() //declared outside the function


    //received an image here
        var imageView = UIImageView() // define the frame according to yourself using frame init method
        imageView.image = image

    if imageViews.isEmpty { // first image view 
    //add constraints to first image view

    let x = NSLayoutConstraint(item: imageView, attribute: .centerX, relatedBy: .equal, toItem: contentView, attribute: .centerX, multiplier: 1.0, constant: 0)
    let y = NSLayoutConstraint(item: imageView, attribute: .top, relatedBy: .equal, toItem: contentView, attribute: .top, multiplier: 1.0, constant: 30)
    let width = NSLayoutConstraint(item: imageView, attribute: .width, relatedBy: .equal, toItem: self.contentView, attribute: .width, multiplier: 1.0, constant: 0)
    let height = NSLayoutConstraint(item: imageView, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 150)
    }

else { //second, third, fourth image view... so on

    let x = NSLayoutConstraint(item: imageView, attribute: .centerX, relatedBy: .equal, toItem: contentView, attribute: .centerX, multiplier: 1.0, constant: 0)
    let y = NSLayoutConstraint(item: imageView, attribute: .top, relatedBy: .equal, toItem: imageViews[imageViews.count - 1], attribute: .bottom, multiplier: 1.0, constant: 30)

    let width = NSLayoutConstraint(item: imageView, attribute: .width, relatedBy: .equal, toItem: self.contentView, attribute: .width, multiplier: 1.0, constant: 0)
    let height = NSLayoutConstraint(item: imageView, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 150)
}

      imageViews.append(imageView) 
}

现在添加与contentView

例如 - 您收到了第一张图片，因此我们将在您的函数之外维护一组UIImageViews。

self.scrollView.contentSize  = CGSize(width, height)

希望你现在有了一个想法，如何解决这个问题。如果有超过4或5个图像视图，您可能需要检查数组的计数并相应地增加scrollView的contentView。你可以通过使用 ArrayBlockingQueue<List<Object>> Q = new ArrayBlockingQueue<List<Object>>(); // producer side List<Object> l = new ArrayList<Object>(); for (int i=0; i<100; i++) { l.add(i); // your initialization here } Q.put(l); // consumer side List<Object> l2 = Q.take(); // do something

Answer 2

我相信你有问题：

let y = NSLayoutConstraint(item: imageView, attribute: .top, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 30)

＆＃34; toItem＆＃34;参数应该有一些价值。第一个参数也应该是imageView.topAnchor。可能看起来应该是这样的：

let y = NSLayoutConstraint(item: imageView.topAnchor, attribute: .top, relatedBy: .equal, toItem: self.contentView.topAnchor, attribute: .notAnAttribute, multiplier: 1.0, constant: 30)

我需要未知元素的顶级约束

2 个答案: