IOSAUTOLAYOUT-无法使高度较小。

Question

Snapkit

我需要在屏幕顶部显示图像视图。它将具有动态高度和宽度的图像。我需要它的顶部边缘与视图的顶部对齐。我需要水平居中。我需要从屏幕大于或等于10的左右边缘。我需要它的高度根据最大高度等于300的内容而动态。我需要保持其纵横比并减少其。根据需要自动使用自动布局自动宽度或高度。 我认为以下代码应该完成工作：

let padding = 10.0
let preview = UIImageView()

preview.setContentHuggingPriority(.required, for: .vertical)
preview.setContentHuggingPriority(.required, for: .horizontal)

preview.backgroundColor = .red
preview.contentMode = .scaleAspectFit
let image = UIImage(named: "demo3")!
preview.image = image

preview.clipsToBounds = true
view.addSubview(preview)
preview.snp.makeConstraints { make in
    make.top.equalTo(view.safeAreaLayoutGuide.snp.top)
    make.centerX.equalToSuperview()
    make.left.right.greaterThanOrEqualToSuperview().inset(padding).priority(.required)
    make.height.lessThanOrEqualTo(300).priority(.required)
    make.width.equalTo(preview.snp.height).multipliedBy(image.size.width / image.size.height).priority(.required)
}

对于景观图像（宽度长于高度），这似乎可以很好地工作，但它在肖像图像中破裂：

景观图像中的工作：

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肖像图像中的模仿。注意高度不再是

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lessThanOrEqualTo(300)

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这是由于Xcode打印的警告，该警告说它无法满足约束，并且必须打破高度约束：

Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<SnapKit.LayoutConstraint:

[email protected]#54 UIImageView:0x7f81b19101e0.centerX == UIView:0x7f81b183dc30.centerX>",
    "<SnapKit.LayoutConstraint:[email protected]#55 UIImageView:0x7f81b19101e0.right >= UIView:0x7f81b183dc30.right - 12.0>",
    "<SnapKit.LayoutConstraint:[email protected]#56 UIImageView:0x7f81b19101e0.height <= 300.0>",
    "<SnapKit.LayoutConstraint:[email protected]#57 UIImageView:0x7f81b19101e0.width == UIImageView:0x7f81b19101e0.height * 0.666748046875>",
    "<NSLayoutConstraint:0x600003e37a20 'UIView-Encapsulated-Layout-Width' UIView:0x7f81b183dc30.width == 430   (active)>"
)

Will attempt to recover by breaking constraint 
<SnapKit.LayoutConstraint:[email protected]#56 UIImageView:0x7f81b19101e0.height <= 300.0>

我本来可以预期它会减小其宽度，同时保持纵横比满足条件。但事实并非如此。

我认为您在这里需要什么是替换

make.left.right.greaterThanOrEqualToSuperview().inset(padding).priority(.required)

make.left.greaterThanOrEqualToSuperview().inset(padding)
make.right.lessThanOrEqualToSuperview().inset(padding)

Answer 1

对于我来说，它现在很好！