Question

是否可以根据条件决定要在对象中定义哪个属性？例如：

props="{
   'prop1': {label: 'Prop1'},
   hasProp2 ? '(prop2': {label: 'Prop2'}) : ('prop3': {label: 'Prop3'}),
   'prop4': {label: 'Prop4'}
}"

假设hasProp2是computed property，其函数返回true或false。如何在对象内部使用ternary operator或基本if statement，甚至有可能？

Answer 1

您可以非常简单地对其进行测试

class DrawingImageView: UIImageView {
    var points: [CGPoint]?
    var path: UIBezierPath?
    var pathLayer: CAShapeLayer!    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        pathLayer = CAShapeLayer()
        pathLayer.fillColor = UIColor.clear.cgColor
        pathLayer.strokeColor = UIColor.clear.withAlphaComponent(0.5).cgColor
        pathLayer.lineWidth = 15
        pathLayer.lineJoin =  .round 
        pathLayer.lineCap =  .round 
        pathLayer.allowsEdgeAntialiasing = true
        pathLayer.allowsGroupOpacity = true
        pathLayer.shadowColor = UIColor.black.cgColor
        pathLayer.shadowOpacity = 1
        pathLayer.shadowOffset = CGSize.zero
        pathLayer.shadowRadius = 5
        self.layer.addSublayer(pathLayer)

        if let touch = touches.first {
            points = [touch.location(in: self)]
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch = touches.first {
            if let coalescedTouches = event?.coalescedTouches(for: touch) {
                points? += coalescedTouches.map { $0.location(in: self) }
            } else {
                points?.append(touch.location(in: self))
            }

            if let predictedTouches = event?.predictedTouches(for: touch) {
                let predictedPoints = predictedTouches.map { $0.location(in: self) }
                pathLayer.path = UIBezierPath.interpolateHermiteFor(points: points! + predictedPoints, closed: false).cgPath
            } else {
                pathLayer.path = UIBezierPath.interpolateHermiteFor(points: points!, closed: false).cgPath
            }
        }
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        pathLayer.path = UIBezierPath.interpolateHermiteFor(points: points!, closed: false).cgPath
        points?.removeAll()
    }
}

如您所见，这是有可能的。 Vue是反应性的，也将起作用。

在对象内部使用三元运算符定义其属性

1 个答案: