Question

我有以下代码：

import SpriteKit
import Foundation

class GameScene: SKScene {
    var occupiedCoordinates: NSMutableArray = NSMutableArray()

    func addShape () {

        //...

        shape.position = CGPoint(x:actualX, y:actualY)
        self.occupiedCoordinates.addObject(NSValue(CGPoint:shape.position))
        let halfDuration = random(min: CGFloat(0.5), max: CGFloat(5))

        //...

        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2*halfDuration), dispatch_get_main_queue(), ^{
            self.occupiedCoordinates.removeObjectAtIndex(0)
            });
    }

}

我使用原始剪切GCD: Dispatch After，我在dispatch_after()

行中收到以下消息

'^' is not a prefix unary operator

任何想法是什么问题？

Answer 1

^{...}是Objective-C语法。您不需要^。

Answer 2

这是将一个闭包（即一个objective-c块）传递给swift函数的正确方法：

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2 * halfDuration), dispatch_get_main_queue(), { () -> () in
    self.occupiedCoordinates.removeObjectAtIndex(0)
})

或者您也可以使用此紧凑形式：

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2 * halfDuration), dispatch_get_main_queue()) {
    self.occupiedCoordinates.removeObjectAtIndex(0)
}

建议阅读：Closures

Swift dispatch_after throw不是前缀一元运算符错误

2 个答案: