• 粒子动画效果.gif

• 粒子动画效果11.gif

Swift---面向协议开发

1. 先创建一个snow.swift文件 这是一个协议

import UIKit
import QuartzCore
protocol snow { // 空的协议
}

extension snow where Self : UIView { 对协议进行拓展 where Self 限定此协议的使用范围只能值UIView
    func createSnow() {
        // 1.创建粒子发射器
        let emitter = self.layer as! CAEmitterLayer
        // 1.1 设置粒子发射器的位置
        emitter.emitterPosition = CGPoint(x: 0, y: 0)
        // 1.2 设置粒子发射器的范围
        emitter.emitterSize = bounds.size
        // 1.3 设置粒子的形状
        emitter.emitterShape = kCAEmitterLayerRectangle
        
        // 2. 创建粒子
        let emitterCell = CAEmitterCell()
        
        // 2.1载入粒子
        emitterCell.contents = UIImage(named: "snowflake1")!.cgImage
        // 2.2设置粒子的出生速率
        emitterCell.birthRate = 400
        // 2.3设置每个粒子的生命周期
        emitterCell.lifetime = 3.5
        // 2.4粒子的颜色
        emitterCell.color = UIColor.white.cgColor
        // 2.5RGBA设置
        emitterCell.redRange = 0.0 // RGBA设置
        emitterCell.blueRange = 0.1
        emitterCell.greenRange = 0.0
        emitterCell.alphaRange = 0.5
        emitterCell.velocity = 9.8 // 重力加速度也就是物理里面G
        emitterCell.velocityRange = 550 // 加速范围
        emitterCell.emissionRange = CGFloat(M_PI_2) // 下落是旋转的角度
        emitterCell.emissionLongitude = CGFloat(-M_PI) //
        emitterCell.yAcceleration = 70
        emitterCell.xAcceleration = 0
        emitterCell.scale = 0.33 // 发射比例
        emitterCell.scaleRange = 1.25
        emitterCell.scaleSpeed = -0.25
        emitterCell.alphaRange = 0.5 // 透明度调整
        emitterCell.alphaSpeed = -0.15
        emitter.emitterCells = [emitterCell] // 载入
    }

}

2. 创建一个继承UIView的SnowView

class SnowView: UIView , snow{

    override init(frame: CGRect) {
        super.init(frame: frame)
        createSnow()
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    // 这个方法一定要重写 不然会在这个位置___let emitter = self.layer as! CAEmitterLayer____报类型不匹配的错误
    override class var layerClass: AnyClass {
        return CAEmitterLayer.self
    }
}

3.创建snowView.添加到控制器的View上

class ViewController: UIViewController {

    var snowview: SnowView?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        snowview = SnowView(frame: CGRect(x: 0, y: 0, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height))
        let snowClipView = UIView(frame: view.bounds)
        snowClipView.clipsToBounds = true
        snowClipView.addSubview(snowview!)
        view.addSubview(snowClipView)
        
    }

}