当我结合 UIPanGestureRecognizer 和自动布局时，我的 UIViews 搞砸了

Question

我想要一个球来跟踪我的手指，因为我在 iPhone 或 iPad 上为每个允许的设备方向沿着圆形轨迹拖动它。当设备旋转时，视图似乎正确居中，但球不会停留在圆周上，当我拖动它时似乎会去任何地方。

编辑

现在根据需要显示。我唯一的额外代码更改是删除不必要的声明 var shapeLayer = CAShapeLayer()

made perfect sense until I tried constraining both ball and trajectory to the view's centre and adding the ball’s centre coordinates as offsets at run time. I followed 中的数学。

有三件事我不明白。

首先，根据两个变量trackRadius和角度theta计算圆的周长，并使用theta的sin和cos求出x 和 y 坐标不会将球放在正确的位置。

其次，使用atan求视图中心与触摸点之间的角度theta，使用trackRadius和theta求x 和 y 坐标不会将球放置或移动到圆周上的新位置。

第三，每当我拖动球时，调试区域中都会显示一条消息 Xcode is Unable to simultaneously satisfy constraints，尽管在拖动球之前没有报告任何约束问题。

这里的问题可能不止一个。我的脑袋开始痛了，如果有人能指出我做错了什么，我将不胜感激。

这是我的代码。

import UIKit

class ViewController: UIViewController {

override var supportedInterfaceOrientations: UIInterfaceOrientationMask { return .all }
var shapeLayer                      = CAShapeLayer()
let track                           = ShapeView()
var ball                            = ShapeView()
var theta                           = CGFloat()

private let trackRadius: CGFloat    = 125
private let ballRadius: CGFloat     = 10

override func viewDidLoad() {
    super.viewDidLoad()
    createTrack()
    createBall()
}

private func createTrack() {
    track.translatesAutoresizingMaskIntoConstraints = false
    track.shapeLayer.path = UIBezierPath(ovalIn: CGRect(x: -trackRadius, y: -trackRadius, width: 2 * trackRadius, height: 2 * trackRadius)).cgPath
    track.shapeLayer.fillColor      = UIColor.clear.cgColor
    track.shapeLayer.strokeColor    = UIColor.red.cgColor
    view.addSubview(track)

    track.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
    track.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
}

private func createBall() {

    let offset = placeBallOnCircumference()

    drawBall()
    constrainBall(offset: offset)

    let touch = UIPanGestureRecognizer(target: self, action:#selector(dragBall(recognizer:)))
    view.addGestureRecognizer(touch)
}

private func placeBallOnCircumference() -> CGPoint {
    let theta: Double = 0                                         // at 0 radians
    let x = CGFloat(cos(theta)) * trackRadius                     // find x and y coords on
    let y = CGFloat(sin(theta)) * trackRadius                     // circle circumference
    return CGPoint(x: x, y: y)
}

func dragBall(recognizer: UIPanGestureRecognizer) {

    var offset = CGPoint()

    let finger : CGPoint = recognizer.location(in: self.view)
    theta  = CGFloat(atan2(Double(finger.x), Double(finger.y)))   // get angle from finger tip to centre
    offset.x = CGFloat(cos(theta)) * trackRadius                  // use angle and radius to get x and
    offset.y = CGFloat(sin(theta)) * trackRadius                  //  y coords on circle circumference

    drawBall()
    constrainBall(offset: offset)
}

private func drawBall() {
    ball.shapeLayer.path = UIBezierPath(ovalIn: CGRect(x: 0, y: 0, width: 2 * ballRadius, height: 2 * ballRadius)).cgPath
    ball.shapeLayer.fillColor    = UIColor.cyan.cgColor
    ball.shapeLayer.strokeColor  = UIColor.black.cgColor
    view.addSubview(ball)
}

private func constrainBall(offset: CGPoint) {
    ball.translatesAutoresizingMaskIntoConstraints = false
    NSLayoutConstraint.activate([
        ball.centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: offset.x),
        ball.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: offset.y),
        ball.widthAnchor.constraint(equalToConstant: trackRadius),
        ball.heightAnchor.constraint(equalToConstant: trackRadius)
        ])
    }
}

Answer 1

主要错误在于

theta = CGFloat(atan2(Double(finger.x), Double(finger.y)))   // get angle from finger tip to centre

没有考虑 center 的视图（或轨迹），并且 atan2() 的参数是错误的（y 排在第一位）。应该是：

theta = atan2(finger.y - track.center.y, finger.x - track.center.x)

另一个问题是你添加的约束越来越多在 func constrainBall() 中，而不删除以前的。您应该保留对约束的引用并修改它们。

最后注意球的width/height约束应该是2*ballRadius，而不是trackRadius。

将它们放在一起（并删除一些不必要的类型转换），它看起来像这样：

var ballXconstraint: NSLayoutConstraint!
var ballYconstraint: NSLayoutConstraint!

override func viewDidLoad() {
    super.viewDidLoad()
    createTrack()
    createBall()

    let touch = UIPanGestureRecognizer(target: self, action:#selector(dragBall(recognizer:)))
    view.addGestureRecognizer(touch)
}

private func createTrack() {
    track.translatesAutoresizingMaskIntoConstraints = false
    track.shapeLayer.path = UIBezierPath(ovalIn: CGRect(x: 0, y: 0, width: 2 * trackRadius, height: 2 * trackRadius)).cgPath
    track.shapeLayer.fillColor      = UIColor.clear.cgColor
    track.shapeLayer.strokeColor    = UIColor.red.cgColor
    view.addSubview(track)

    track.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
    track.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
    track.widthAnchor.constraint(equalToConstant: 2 * trackRadius).isActive = true
    track.heightAnchor.constraint(equalToConstant: 2 * trackRadius).isActive = true
}

private func createBall() {

    // Create ball:
    ball.translatesAutoresizingMaskIntoConstraints = false
    ball.shapeLayer.path = UIBezierPath(ovalIn: CGRect(x: 0, y: 0, width: 2 * ballRadius, height: 2 * ballRadius)).cgPath
    ball.shapeLayer.fillColor    = UIColor.cyan.cgColor
    ball.shapeLayer.strokeColor  = UIColor.black.cgColor
    view.addSubview(ball)

    // Width/Height contraints:
    ball.widthAnchor.constraint(equalToConstant: 2 * ballRadius).isActive = true
    ball.heightAnchor.constraint(equalToConstant: 2 * ballRadius).isActive = true

    // X/Y constraints:
    let offset = pointOnCircumference(0.0)
    ballXconstraint = ball.centerXAnchor.constraint(equalTo: track.centerXAnchor, constant: offset.x)
    ballYconstraint = ball.centerYAnchor.constraint(equalTo: track.centerYAnchor, constant: offset.y)
    ballXconstraint.isActive = true
    ballYconstraint.isActive = true
}

func dragBall(recognizer: UIPanGestureRecognizer) {

    let finger = recognizer.location(in: self.view)

    // Angle from track center to touch location:
    theta = atan2(finger.y - track.center.y, finger.x - track.center.x)

    // Update X/Y contraints of the ball:
    let offset = pointOnCircumference(theta)
    ballXconstraint.constant = offset.x
    ballYconstraint.constant = offset.y
}


private func pointOnCircumference(_ theta: CGFloat) -> CGPoint {
    let x = cos(theta) * trackRadius
    let y = sin(theta) * trackRadius
    return CGPoint(x: x, y: y)
}

当我结合 UIPanGestureRecognizer 和自动布局时，我的 UIViews 搞砸了

my UIViews muck-up when I combine UIPanGestureRecognizer and autolayout

uiview

ios

uipangesturerecognizer

autolayout

swift