iOS"UITemporaryLayoutHeight"约束

Question

我systemLayoutSizeFittingSize用来获得满足其内部约束的自定义视图子类的最小大小.

let someView = SomeView()        
someView.setNeedsUpdateConstraints()
someView.setNeedsLayout()
someView.layoutIfNeeded()

let viewSize = someView.systemLayoutSizeFittingSize(UILayoutFittingCompressedSize)

println(viewSize) // PRINTS (0.0, 96.0) WHICH IS RIGHT!

我得到正确的值,但我也收到Unable to simultaneously satisfy constraints警告:

"<NSLayoutConstraint:0x7ff16b753190 '_UITemporaryLayoutHeight' V:[ProjectName.SomeView:0x7ff16b772210(0)]>",
"<NSLayoutConstraint:0x7ff16b75de50 UIImageView:0x7ff16b76eff0.top == ProjectName.SomeView:0x7ff16b772210.topMargin>",
"<NSLayoutConstraint:0x7ff16b7653f0 UIImageView:0x7ff16b76eff0.bottom <= ProjectName.SomeView:0x7ff16b772210.bottomMargin>"

下面是我的SomeViewUIView子类.

它只包含固定在顶部,左侧和底部边距的80x80 imageView.(我使用PureLayout编写约束).

现在很明显,这个视图的固定高度为96(边距为80 + 8x2)但理论上如果它的子视图改变了大小,它可以拉伸.

有任何想法吗？搜索谷歌UITemporaryLayoutHeight(或宽度)给出0结果...

class SomeView: UIView {

    let imageView = UIImageView()

    var constraintsSet = false

    override init(frame: CGRect) {

        super.init(frame: frame)

        backgroundColor = UIColor.lightGrayColor()

        imageView.backgroundColor = UIColor.darkGrayColor()
        addSubview(imageView)
    }

    override func updateConstraints() {

        if(!constraintsSet) {

            imageView.autoPinEdgeToSuperviewMargin(.Top)
            imageView.autoPinEdgeToSuperviewMargin(.Left)
            imageView.autoPinEdgeToSuperviewMargin(.Bottom, relation: NSLayoutRelation.GreaterThanOrEqual)
            imageView.autoSetDimension(.Width, toSize: 80.0)
            imageView.autoSetDimension(.Height, toSize: 80.0)

            constraintsSet = true
        }
        super.updateConstraints()
    }
}

Answer 1

我已经注意到,如果我layoutIfNeeded在父母布局之前调用了一个视图,就会发生这种情况.我敢打赌如果你删除someView.layoutIfNeeded()你就不会再看到那个错误.您可能也可以摆脱someView.setNeedsLayout()并替换它someView.updateConstraintsIfNeeded().systemLayoutSizeFittingSize不应该要求实际布置视图,只需要正确配置约束.

Answer 2

这个:

它只包含固定在顶部,左侧和底部边距的80x80 imageView

还有这个

NSLayoutConstraint:0x7ff16b753190'_UITemporaryLayoutHeight'V:[ProjectName.SomeView:0x7ff16b772210(0)]

是问题的根源.UIKit在加载/布局/显示过程中的某个点使用高度为0.由于您对顶部和底部都有约束并且 imageview具有其固有内容大小,因此您告诉它将图像拟合到零垂直空间.

解决此问题的常用方法是将top或bottom约束的优先级设置为小于1000的任何值.

Answer 3

当视图没有superview并且layoutIfNeeded被调用时,我收到了此警告.我的解决方案是layoutIfNeeded在视图添加到a后调用superview.我希望这有帮助:

- (void)didMoveToSuperview {
    [super didMoveToSuperview];
    [self layoutIfNeeded];
}