使用CGPath创建一个子视图，然后在该子视图上添加UIPanGestureRecognizer

Question

I have seen several answers about adding a GestureRecognzier to subViews but my problem is that I don't have the subView's frame available beforehand. I am drawing a CGPath and at the Touches Ended method, I want to create a new subView with frame equal to CGPath bounding box. After that, I want to drag that subView with PanGestureRecognizer . I am trying to implement Evernote crop functionality where the user selects a certain area of view and move it to other position. Is this the right approach to that solution?

Answer 1

Not quite understand the relationship between UIGestureRecognizer and .frame . you can simply add UIGestureRecognizer to object, once its init work finished. Try to add gesture in TouchEnd method directly after drawing subview.

import UIKit

class GestureResearchVC: UIViewController{

    var subViewByCGPath: UIView?

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

    func createSubView(){
        //creat subview
        subViewByCGPath = UIView(frame: CGRect(x: 100, y: 100, width: 100, height: 100))
        subViewByCGPath?.backgroundColor = UIColor.yellow
        let circlePath = UIBezierPath(arcCenter: CGPoint(x: 50,y: 50), radius: CGFloat(20), startAngle: CGFloat(0), endAngle:CGFloat(M_PI * 2), clockwise: true)

        let shapeLayer = CAShapeLayer()
        shapeLayer.path = circlePath.cgPath
        shapeLayer.strokeColor = UIColor.red.cgColor

        subViewByCGPath?.layer.addSublayer(shapeLayer)
        self.view.addSubview(subViewByCGPath!)

        //add pan gesture to subViewByCGPath
        let gesture = UIPanGestureRecognizer(target: self, action: #selector(panGestureAction(rec:)))
        subViewByCGPath?.addGestureRecognizer(gesture)
}

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        if subViewByCGPath == nil {
            print("touch end once")
            createSubView()
        }else{
            print("touch end repeatedly")
        }
    }

    func panGestureAction(rec: UIPanGestureRecognizer){
        print("pannnnnnn~")
        let transPoint = rec.translation(in: self.view)
        let x = rec.view!.center.x + transPoint.x
        let y = rec.view!.center.y + transPoint.y

        rec.view!.center = CGPoint(x: x, y: y)
        rec.setTranslation(CGPoint(x: 0, y: 0), in: self.view)

        //distinguish state
        switch rec.state {
            case .began:
                print("began")
            case .changed:
                print("changed")
            case .ended:
                print("ended")
            default:
                print("???")
        }
    }
}