当我结合使用UIPanGestureRecognizer和自动布局时,我的UIViews混乱了

Question

当我在iPhone或iPad上为每个允许的设备方向拖动它时,我想要一个球来跟踪我的手指.当旋转设备时,视图似乎正确居中,但是当我拖动它时,球不会停留在圆周上并且似乎在任何地方.

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编辑

Martin R的答案现在按要求显示.我唯一的额外代码更改是删除不必要的声明var shapeLayer = CAShapeLayer()

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在我尝试将球和轨迹都限制在视图中心并将球的中心坐标作为偏移量添加到运行时之前,这个例子中的数学非常有意义.我遵循了有关如何约束视图的这些建议.

有三件事我不明白.

首先,从两个变量计算圆的周长trackRadius和角度theta,并使用sin和cos的theta发现x和y坐标不会把球在合适的位置.

其次,atan用于找到theta视图中心与被触摸点之间的角度,并使用trackRadiuswith theta来查找x和y坐标不会将球放置或沿圆周移动到新的位置.

第三,每当我拖动球时,调试区域中的消息都会显示Xcode is Unable to simultaneously satisfy constraints,尽管在拖动之前没有报告任何约束问题.

这里可能存在多个问题.我的大脑开始受到伤害,如果有人能够指出我做错了什么,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

主要错误是

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

不考虑视图（或轨道）中心，并且 的参数atan2()是错误的（y 首先）。它应该是：

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

另一个问题是您在 中添加了越来越多的约束func constrainBall()，而没有删除以前的约束。您应该保留对约束的引用并修改它们。

最后请注意，球的宽度/高度约束应该是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)
}