iOS自动布局通过VFL编程实现

Question

我已经使用自动布局在情节提要中设计了视图，但是使用VFL以编程方式实现此功能时遇到了一些问题。 此视图的肖像如下

有三个子视图以某种顺序垂直排列，并且可以通过某种方法更改它们的顺序（即[1,2,3]到[2,3,1]）。 view1，view2，view3都具有固定的width = 100和height = 100，view2的中心等于其superview的中心。 更改为横向模式时，三个子视图以与纵向相同的顺序水平布局，如下所示：

希望有人可以帮助我实现这一目标，谢谢您的帮助！ 如果我没有明确描述我的问题，您可以在这里下载我的示例项目！ https://github.com/SomnusLee1988/SamplePorject

Answer 1

由于您无法设置约束，仅使用VFL就可以满足所有要求，因此可以采用以下解决方案：

var view1: UIView!
var view2: UIView!
var view3: UIView!

var variableConstraints = [NSLayoutConstraint]()

let metrics = ["width": 100, "height": 100]
var views: [String: AnyObject]!

override func viewDidLoad() {
    super.viewDidLoad()

    view1 = UIView()
    view1.backgroundColor = UIColor.redColor()
    view1.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(view1)

    view2 = UIView()
    view2.backgroundColor = UIColor.blueColor()
    view2.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(view2)

    view3 = UIView()
    view3.backgroundColor = UIColor.greenColor()
    view3.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(view3)

    views = ["v1": view1, "v2": view2, "v3": view3]

    setupFixedConstraints()
    setupVariableConstraintsForSize(nil)
}

private func setupFixedConstraints() {
    // width and height
    NSLayoutConstraint.activateConstraints(NSLayoutConstraint.constraintsWithVisualFormat("[v2(width)]", options: [], metrics: metrics, views: views))
    NSLayoutConstraint.activateConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:[v2(height)]", options: [], metrics: metrics, views: views))

    // center x and center y
    NSLayoutConstraint(item: view2, attribute: .CenterX, relatedBy: .Equal, toItem: view, attribute: .CenterX, multiplier: 1, constant: 0).active = true
    NSLayoutConstraint(item: view2, attribute: .CenterY, relatedBy: .Equal, toItem: view, attribute: .CenterY, multiplier: 1, constant: 0).active = true
}

private func setupVariableConstraintsForSize(size: CGSize?) {
    // remove existing constraints
    NSLayoutConstraint.deactivateConstraints(variableConstraints)
    variableConstraints.removeAll()

    let size = size ?? view.frame.size

    if size.width > size.height {
        // landscape
        variableConstraints += NSLayoutConstraint.constraintsWithVisualFormat("[v1(==v2)][v2][v3(==v2)]", options: [.AlignAllTop, .AlignAllBottom], metrics: metrics, views: views)
    } else {
        // portrait
        variableConstraints += NSLayoutConstraint.constraintsWithVisualFormat("V:[v1(==v2)][v2][v3(==v2)]", options: [.AlignAllLeading, .AlignAllTrailing], metrics: metrics, views: views)
    }

    // activate constraints
    NSLayoutConstraint.activateConstraints(variableConstraints)
}

override func viewWillTransitionToSize(size: CGSize, withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator) {
    setupVariableConstraintsForSize(size)
    super.viewWillTransitionToSize(size, withTransitionCoordinator: coordinator)
}