在 Swift 中結束 CAEmitterLayer 的正確方法是什么？

Question

我經常在 Swift 中看到連續發射器的例子，我在 Obj-C 中找到了一個例子，將發射器單元的出生率設置為 0.0，但它似乎不起作用，所以我一定是做錯了什么. 在我的示例中，我可以看到出生率設置為 0 的消息有 16 次，但粒子繼續無休止地流動。

@IBAction func particleBtnAction(_ sender: Any) {

    let emitter = CAEmitterLayer()
    emitter.emitterPosition = CGPoint(x: self.view.frame.size.width / 2, y: -10)
    emitter.emitterShape = kCAEmitterLayerLine
    emitter.emitterSize = CGSize(width: self.view.frame.size.width, height: 2.0)
    emitter.emitterCells = generateEmitterCells()
    self.view.layer.addSublayer(emitter)

    // perform selector after 1.5 seconds when particles start
    perform(#selector(endParticles), with: emitter, afterDelay: 1.5)

}

private func generateEmitterCells() -> [CAEmitterCell] {

    var cells:[CAEmitterCell] = [CAEmitterCell]()
    for index in 0..<16 {
        let cell = CAEmitterCell()
        cell.birthRate = 4.0
        cell.lifetime = 1.0
        cell.lifetimeRange = 0
        cell.velocity = 0.7
        cell.velocityRange = 0
        cell.emissionLongitude = CGFloat(Double.pi)
        cell.emissionRange = 0.5
        cell.spin = 3.5
        cell.spinRange = 0
        cell.scaleRange = 0.25
        cell.scale = 0.1
        cells.append(cell)
    }
    return cells
}

@objc func endParticles(emitterLayer:CAEmitterLayer) {

    for emitterCell in emitterLayer.emitterCells! {
        emitterCell.birthRate = 0.0
        print("birth rate set to 0")
    }

}

Answer 1

將CAEmitterLayer的lifetime設置為零會停止發射任何新的發射器emitterCells ：

@objc func endParticles(emitterLayer:CAEmitterLayer) {
    emitterLayer.lifetime = 0.0
}

Answer 2

您可以使用鍵路徑為每個單元格分配一個名稱並遍歷它們，在您想要更改它們時更改每個單元格的屬性：

private func generateEmitterCells() -> [CAEmitterCell] {

    var cells:[CAEmitterCell] = [CAEmitterCell]()
    for index in 0..<16 {
        let cell = CAEmitterCell()
        cell.birthRate = 4.0
        cell.lifetime = 1.0
        cell.lifetimeRange = 0
        cell.velocity = 0.7
        cell.velocityRange = 0
        cell.emissionLongitude = CGFloat(Double.pi)
        cell.emissionRange = 0.5
        cell.spin = 3.5
        cell.spinRange = 0
        cell.scaleRange = 0.25
        cell.scale = 0.1
        cell.name = "cell\(index)" // cell name
        cells.append(cell)
    }
    return cells
}

@objc func endParticles(emitterLayer:CAEmitterLayer) {

    for i in 0..<(emitterLayer.emitterCells?.count ?? 0){

        emitterLayer.setValue(0.0, forKeyPath: "emitterCells.cell\(i).birthRate")
        print("birth rate set to 0")

    }

}

Answer 3

當您想要結束粒子時，您可以嘗試設置 isHidden 屬性

emitter.isHidden = true

但請注意，所有細胞都會立即消失，無論它們何時被發射，或者它們的生命周期。

另一種可能性是將所有與比例相關的屬性設置為 0，然后壽命和出生率就無關緊要，因為新發射的細胞將不可見。

cell.scaleSpeed = 0
cell.scaleRange = 0
cell.scale = 0