可拖动的label

//
//  DragLabel.swift
//
//  Created by 浩哥 on 2018/4/18.
//  Copyright © 2018年 HarrySun. All rights reserved.
//

import UIKit

class DragLabel: UILabel {

    override func touchesMoved(_ touches: Set, with event: UIEvent?) {
        super.touchesMoved(touches, with: event)
        let touch = touches.first
        let current =  touch?.location(in: self)
        let previous = touch?.previousLocation(in: self)
        var center = self.center
        guard let currentX = current?.x,
            let currentY = current?.y,
            let previousX = previous?.x,
            let previousY = previous?.y else {
                return
        }
        
        center.x += CGFloat(currentX - previousX)
        center.y += CGFloat(currentY - previousY)
        
        // 控制控件的可拖动范围
        if let superview = self.superview, frame.origin.x < superview.bounds.origin.x {
            center.x = frame.size.width / 2
        }
        if let superview = self.superview, frame.origin.x > superview.bounds.size.width - frame.size.width {
            center.x = superview.bounds.size.width - frame.size.width / 2
        }
        if let superview = self.superview, frame.origin.y < superview.bounds.origin.y {
            center.y = frame.size.height / 2
        }
        if let superview = self.superview, frame.origin.y > superview.bounds.size.height - frame.size.height - 20 {
            center.y = superview.bounds.size.height - frame.size.height / 2 - 20
        }
        
        self.center = center
    }
}