如何解决在Autolayout下设置其图层的anchorPoint后如何使uiview不移动
我有一个需求,需要更改UIView层的anchorPoint,但是更改anchorPoint后视图无法移动。 我知道当视图由框架(CGRect:...)定义时是可能的。像这样:
let width = SCREEN_WIDTH - 40
let view2 = UIView(frame: CGRect(x: 20,y: 300,width: width,height: 200))
view2.backgroundColor = .blue
self.view.addSubview(view2)
let oldFrame2 = view2.frame
view2.layer.anchorPoint = CGPoint(x: 0,y: 0.5)
view2.frame = oldFrame2
这有效。
但是我的视图是由 Autolayout 定义的,我尝试了上面代码的解决方案,但它不起作用。代码:
let view1 = UIView()
view1.backgroundColor = .orange
self.view.addSubview(view1)
view1.snp.makeConstraints { (maker) in
maker.top.equalToSuperview().offset(50)
maker.leading.equalToSuperview().offset(20)
maker.trailing.equalToSuperview().offset(-20)
maker.height.equalTo(200)
}
let oldFrame1 = view1.frame
view1.layer.anchorPoint = CGPoint(x: 0,y: 0.5)
view1.frame = oldFrame1
结果是:橙色的view1被移动了,改变anchorPoint后应该和蓝色的view2一样。
谁能给我一些建议?
------------------------------更新答案-------------- --------------
正如@DonMag 的回答,我们可以通过在使用 Autolayout 时更新视图而非框架的约束来实现这一要求。这是 SnapKit 的代码:
let view1 = UIView()
view1.backgroundColor = .orange
view1.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(view1)
view1.snp.makeConstraints { (maker) in
maker.top.equalToSuperview().offset(100)
maker.leading.equalToSuperview().offset(20)
maker.trailing.equalToSuperview().offset(-20)
maker.height.equalTo(200)
}
// important!!!
view1.layoutIfNeeded()
let oldFrame1 = view1.frame
view1.layer.anchorPoint = CGPoint(x: 0,y: 0.5)
// update constraints by updateConstraints function
// if you use @IBOutlet NSLayoutConstraint from xib,// you can also just set xxx.constant = yyy to update the constraints.
view1.snp.updateConstraints { (maker) in
let subOffset = oldFrame1.width * 0.5
maker.leading.equalToSuperview().offset(20 - subOffset)
maker.trailing.equalToSuperview().offset(-20 - subOffset)
}
let width = SCREEN_WIDTH - 40
let view2 = UIView(frame: CGRect(x: 20,y: 0.5)
view2.frame = oldFrame2
另一种解决方案是通过设置 translatesAutoresizingMaskIntoConstraints = true
将自动布局视图更改为框架,如下所示:
let width = SCREEN_WIDTH - 40
let view1 = UIView()
view1.backgroundColor = .orange
self.view.addSubview(view1)
// Autolayout
view1.snp.makeConstraints { (maker) in
maker.top.equalToSuperview().offset(100)
maker.leading.equalToSuperview().offset(20)
maker.trailing.equalToSuperview().offset(-20)
maker.height.equalTo(200)
}
// change autolayout to frame
view1.translatesAutoresizingMaskIntoConstraints = true
view1.frame = CGRect(x: 20,y: 100,height: 200)
let oldFrame1 = view1.frame
view1.layer.anchorPoint = CGPoint(x: 0,y: 0.5)
view1.frame = oldFrame1
let view2 = UIView(frame: CGRect(x: 20,y: 0.5)
view2.frame = oldFrame2
解决方法
首先,当使用自动布局/约束时,直接设置视图的 .frame
不会给出预期的结果。自动布局更新 UI 后,将重新应用约束。
当您更改 .anchorPoint
时,您会更改视图的几何形状。因此,最好使用 .frame
而不是自动布局。
如果您确实需要/想要使用自动布局,则需要更新约束的 .constant
值以应对几何变化。
我不知道如何使用 SnapKit 做到这一点,但这里有一个使用“标准”约束语法的示例。
- 声明前导和尾随约束变量
- 分配和激活约束
- 告诉自动布局计算框架
- 改变锚点
- 更新 Lead 和 Trailing 约束常量以反映几何变化
注意:这只是示例代码!:
class ViewController: UIViewController {
// these will have their .constant values changed
// to account for layer.anchorPoint change
var leadingConstraint: NSLayoutConstraint!
var trailingConstraint: NSLayoutConstraint!
override func viewDidLoad() {
super.viewDidLoad()
// NOT using auto-layout constraints
let width = view.frame.width - 40
let view2 = UIView(frame: CGRect(x: 20,y: 300,width: width,height: 200))
view2.backgroundColor = .blue
self.view.addSubview(view2)
let oldFrame2 = view2.frame
view2.layer.anchorPoint = CGPoint(x: 0,y: 0.5)
view2.frame = oldFrame2
// USING auto-layout constraints
let view1 = UIView()
view1.backgroundColor = .orange
view1.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(view1)
// create leading and trailing constraints
leadingConstraint = view1.leadingAnchor.constraint(equalTo: view.leadingAnchor,constant: 20.0)
trailingConstraint = view1.trailingAnchor.constraint(equalTo: view.trailingAnchor,constant: -20.0)
// activate constraints
NSLayoutConstraint.activate([
view1.topAnchor.constraint(equalTo: view.topAnchor,constant: 80.0),view1.heightAnchor.constraint(equalToConstant: 200.0),leadingConstraint,trailingConstraint,])
// auto-layout has not run yet,so force it to layout
// the view frame
view1.layoutIfNeeded()
// get the auto-layout generated frame
let oldFrame1 = view1.frame
// change the anchorPoint
view1.layer.anchorPoint = CGPoint(x: 0,y: 0.5)
// we've move the X anchorPoint from 0.5 to 0.0,so
// we need to adjust the leading and trailing constants
// by 0.5 * the frame width
leadingConstraint.constant -= oldFrame1.width * 0.5
trailingConstraint.constant -= oldFrame1.width * 0.5
}
}
结果:
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