ios – 如何以编程方式快速设置自动布局中的UIView大小？

我使用以下代码制作了两个带有自动布局的UIView：

class ViewController: UIViewController {

    var view_constraint_V:NSArray = [NSLayoutConstraint]();
    var originalValue:CGFloat = 0.0;
    var offsetValue:CGFloat = -100;

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view,typically from a nib.
        var topView = UIView()
        topView.setTranslatesAutoresizingMaskIntoConstraints(false)
        topView.backgroundColor = UIColor.blackColor()

        var bottomView = UIView()
        bottomView.setTranslatesAutoresizingMaskIntoConstraints(false)
        bottomView.backgroundColor = UIColor.lightGrayColor()

        let button   = UIButton()
        button.backgroundColor = UIColor.darkGrayColor()
        button.setTitle("Click me!",forState: UIControlState.normal)
        button.addTarget(self,action: "buttonAction:",forControlEvents: UIControlEvents.TouchUpInside)
        button.setTranslatesAutoresizingMaskIntoConstraints(false)

        self.view.addSubview(topView);
        self.view.addSubview(bottomView);
        bottomView.addSubview(button)

        // constraints
        let viewsDictionary = ["top":topView,"bottom":bottomView,"button":button]

        //position constraints
        let view_constraint_H:NSArray = NSLayoutConstraint.constraintsWithVisualFormat("H:|-10-[top]-10-|",options: NSLayoutFormatOptions(0),metrics: nil,views: viewsDictionary)
        let view_constraint_H2:NSArray = NSLayoutConstraint.constraintsWithVisualFormat("H:|-10-[bottom]-10-|",views: viewsDictionary)

        view_constraint_V = NSLayoutConstraint.constraintsWithVisualFormat("V:|-20-[top(bottom)]-[bottom]-10-|",options: NSLayoutFormatOptions.AlignAllLeading,views: viewsDictionary)

        view.addConstraints(view_constraint_H)
        view.addConstraints(view_constraint_H2)
        view.addConstraints(view_constraint_V)

        originalValue = (view_constraint_V[1] as NSLayoutConstraint).constant;
      //println((view_constraint_V[1] as NSLayoutConstraint))
        (view_constraint_V[1] as NSLayoutConstraint).constant = offsetValue

        // Position button
        let control_constraint_H:NSArray = NSLayoutConstraint.constraintsWithVisualFormat("H:|-30-[button]-30-|",views: viewsDictionary)
        let control_constraint_V:NSArray = NSLayoutConstraint.constraintsWithVisualFormat("V:|-30-[button(50)]",views: viewsDictionary)

        bottomView.addConstraints(control_constraint_H)
        bottomView.addConstraints(control_constraint_V)

    }
    /**
        Example of dynamically changing the constraints when clicking on a button.
    */
    func buttonAction(sender:UIButton!)
    {
        if (view_constraint_V[1].constant == offsetValue) {
            (view_constraint_V[1] as NSLayoutConstraint).constant = originalValue
        } else {
            (view_constraint_V[1] as NSLayoutConstraint).constant = offsetValue
        }
    }
}

现在,我想以编程方式将顶视图大小设置为底视图大小的1/3,但我不知道如何执行此操作.

解决方法

这将有效：

let heightConstraint = NSLayoutConstraint(item: topView,attribute: NSLayoutAttribute.Height,relatedBy: NSLayoutRelation.Equal,toItem: bottomView,multiplier: 0.33,constant: 0)
self.view.addConstraint(heightConstraint)

let widthConstraint = NSLayoutConstraint(item: topView,attribute: NSLayoutAttribute.Width,constant: 0)

self.view.addConstraint(widthConstraint)