ios 以编程方式修改约束 Swift
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Modify constraint programmatically Swift
提问by H4Hugo
I have the following view controller in my storyboard :
我的故事板中有以下视图控制器：
It will always have 6 image views that are, by default, equal in widths and heights. Each image view is constrained to the superview with : "equal heights" and a multiplier of 1/2.
它总是有 6 个图像视图，默认情况下，宽度和高度相等。每个图像视图都被限制在父视图中：“等高”和 1/2 的乘数。
However, before I load images inside, I read a property that gives me the desired height for an image (width will never be modified).
但是，在我加载图像之前，我读取了一个属性，该属性为我提供了所需的图像高度（永远不会修改宽度）。
So my interface (at runtime) can look like this :
所以我的界面（在运行时）可以是这样的：
I think I need to modify the multiplier constant but it's read-only.
我想我需要修改乘数常数，但它是只读的。
I saw posts saying that we can update the constantproperty of the constraint but it's in points, I need it to work on every device.
我看到帖子说我们可以更新约束的常量属性，但它是点数，我需要它在每个设备上工作。
Now what would you recommend ? Should I remove the constraint and add a new one ? If I don't remove it and try to apply a new height constraint, will it be removed automatically for me ?
现在你会推荐什么？我应该删除约束并添加一个新约束吗？如果我不删除它并尝试应用新的高度约束，它会自动为我删除吗？
Do I have to use pods like snapkit to do the job ?
我是否必须使用 snapkit 之类的 pod 来完成这项工作？
Thanks for your help.
谢谢你的帮助。
EDIT
编辑
Here is the code I tried, but did not succeeded :
这是我尝试过的代码，但没有成功：
for (index, (drawing, ratio)) in drawingElements.enumerate() {
drawingViews[index].image = UIImage(named: drawing)
// update height constraint if ratio is different than defaut ratio of 1/2
if ratio != 0.5 {
heightConstraints[index].active = false
let newHeightConstraint = NSLayoutConstraint(item: drawingViews[index], attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.Height, multiplier: ratio, constant: 0)
drawingViews[index].addConstraint(newHeightConstraint)
self.view.layoutIfNeeded()
}
}
Am I doing it wrong ? I am unsure about the new height constraint though
我做错了吗？虽然我不确定新的高度限制
采纳答案by H4Hugo
So this is the way I achieved this :
所以这是我实现这一目标的方式：
Create a constraint programmatically(height in my case) :
// Drawing height property var drawingHeightConstraint: NSLayoutConstraint?Deactivate old constraint and set the new one if needed
以编程方式创建约束（在我的情况下为高度）：
// Drawing height property var drawingHeightConstraint: NSLayoutConstraint?停用旧约束并根据需要设置新约束
Note: heightContraints is an array of NSLayoutConstraint which contains my outlets
注意：heightContraints 是一个包含我的插座的 NSLayoutConstraint 数组
for (index, (drawing, ratio)) in drawingElements.enumerate() {
drawingViews[index].image = UIImage(named: drawing)
// update height constraint if ratio is different than defaut ratio of 1/2
if ratio != 0.5 {
heightConstraints[index].active = false
drawingHeightConstraint = NSLayoutConstraint(item: drawingViews[index], attribute: .Height, relatedBy: .Equal, toItem: drawingView, attribute: .Height, multiplier: CGFloat(ratio), constant: 0)
drawingHeightConstraint!.active = true
}
}
- Call layoutIfNeeded() right after (note: not sure when to call it)
- 立即调用 layoutIfNeeded() （注意：不确定何时调用它）
回答by Karaban
The constraints constants are related to the content of the constrained element. That why you're getting such screen. The easiest way - create image with clear color and set it by default. After downloading completed just set new image for your imageView
约束常量与受约束元素的内容有关。这就是为什么你会得到这样的屏幕。最简单的方法 - 创建颜色清晰的图像并默认设置。下载完成后，只需为您的 imageView 设置新图像
Or you can set IBOutlet for your height constraint - and change it value for different situations i.e.
或者您可以为您的高度限制设置 IBOutlet - 并针对不同情况更改它的值，即
if(download.completed)
ibHeightOutlet.constant = imageView.frame.size.height;
else
ibHeightOutlet.constant = initialImageViewHeght.frame.size.height;
回答by FreeNickname
You can not change the multiplier for reasons unknown to me (some kind of Apple's implementation detail probably). You can remove a constraint and create a new one, however. You have to remove the old constraint, because it will not be removed automatically, and you'll get a conflict. Alternatively, you could create the first constraint (with the 0.5multiplier) with lower priority. This way you could keep it (autolayout would just ignore it), but I don't think it is a way to go, since why would you need that unnecessary constraint? Just delete it.
As for third-party layout engines and libraries –?unfortunately, I can't give you any advice here.
由于我不知道的原因（可能是某种 Apple 的实现细节），您无法更改乘数。但是，您可以删除约束并创建新约束。您必须删除旧约束，因为它不会自动删除，并且会发生冲突。或者，您可以创建0.5优先级较低的第一个约束（使用乘数）。这样你就可以保留它（自动布局会忽略它），但我不认为这是一种方法，因为你为什么需要这种不必要的约束？删除它就行了。至于第三方布局引擎和库——不幸的是，我不能在这里给你任何建议。
