当我沿着圆形轨迹拖动手指时,我想要一个球来跟踪我的手指,以适应 iPhone 或 iPad 上每个允许的设备方向。当设备旋转时,视图似乎正确居中,但球不会停留在圆周上,并且当我拖动它时,它似乎会去任何地方。
EDIT
马丁·R的回答 https://stackoverflow.com/a/40890891/2348597现在根据需要显示此内容。我唯一的额外代码更改是删除不必要的声明var shapeLayer = CAShapeLayer()
数学中这个例子 https://stackoverflow.com/a/37614895/2348597直到我尝试将球和轨迹限制到视图中心并在运行时添加球的中心坐标作为偏移量为止,这是完全有意义的。我跟着这些关于如何约束视图的建议 https://stackoverflow.com/a/40661596/2348597.
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
and cos
of theta
找到x
and y
坐标不会将球放置在正确的位置。
二、使用atan
找到角度theta
在视图中心和触摸点之间,并使用trackRadius
with theta
找到x
and y
坐标不会将球放置或移动到沿圆周的新位置。
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
,尽管在拖动之前没有报告任何约束问题。
这里可能存在不止一个问题。我的大脑开始受伤,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)
])
}
}