swift - 在 macOS 中使用空格键添加 SKSpriteNode

Question

我正在使用基本的 Breakout 游戏框架。我想使用空格键添加球。我已经到了球出现的地步，但我没有施加冲动，所以它们弹跳起来。我还希望它们的生命周期为 x 秒。这是代码的相关压缩部分。

我在 OSX/macOS 上使用 Xcode 9 而不是 iOS swift 4 10.13.2

    override func keyDown(with event: NSEvent) {
        let keyEvent = event.characters
        if keyEvent == " "{print("space bar")

            // Create sprite
            let myBall = SKSpriteNode(imageNamed: "greenball")
            myBall.zPosition = 1
            myBall.xScale = 1
            myBall.yScale = 1

            // Determine where to spawn the ball along the Y axis
            let actualY:CGFloat = CGFloat(arc4random_uniform(624))-312.0

            // Position the ball
            myBall.position = CGPoint(x: 460.0, y: actualY)

            // Determine speed of the ball
            let actualDuration:CGFloat = 4.0

            myBall.physicsBody?.isDynamic = true
            myBall.physicsBody?.affectedByGravity = true
            myBall.physicsBody?.friction = 1
            myBall.physicsBody?.restitution = 1
            myBall.physicsBody?.mass = 0.0035744346678257

            addChild(myBall)

            myBall.physicsBody?.applyImpulse(CGVector(dx: 300.0, dy: -300.0))//<--this does not fore ??
        }
    }

Answer 1

您需要始终记住创建一个物理体。我会推荐使用!代替 ？当你处理可选项时。利用 ？只有当你希望你的结果为零时，否则你希望你的程序在调试期间崩溃，以便你知道你有错误。

override func keyDown(with event: NSEvent) {
    let keyEvent = event.characters
    if keyEvent == " "{print("space bar")

        // Create sprite
        let myBall = SKSpriteNode(imageNamed: "greenball")
        myBall.zPosition = 1
        myBall.xScale = 1
        myBall.yScale = 1

        // Determine where to spawn the ball along the Y axis
        let actualY:CGFloat = CGFloat(arc4random_uniform(624))-312.0

        // Position the ball
        myBall.position = CGPoint(x: 460.0, y: actualY)

        // Determine speed of the ball
        let actualDuration:CGFloat = 4.0
        myBall.physicsBody = SKPhysicsBody(circleOfRadius:myBall.size.width /2 )
        myBall.physicsBody!.isDynamic = true
        myBall.physicsBody!.affectedByGravity = true
        myBall.physicsBody!.friction = 1
        myBall.physicsBody!.restitution = 1
        myBall.physicsBody!.mass = 0.0035744346678257

        addChild(myBall)

        myBall.physicsBody!.applyImpulse(CGVector(dx: 300.0, dy: -300.0))//<--this does not fore ??
    }
}

如果你决定不想偷懒，想写出更干净的代码，那么我建议做 if let 或 guard let

override func keyDown(with event: NSEvent) {
    let keyEvent = event.characters
    if keyEvent == " "{
        print("space bar")

        // Create sprite
        let myBall = SKSpriteNode(imageNamed: "greenball")
        myBall.zPosition = 1
        myBall.xScale = 1
        myBall.yScale = 1

        // Determine where to spawn the ball along the Y axis
        let actualY:CGFloat = CGFloat(arc4random_uniform(624))-312.0

        // Position the ball
        myBall.position = CGPoint(x: 460.0, y: actualY)

        // Determine speed of the ball
        let actualDuration:CGFloat = 4.0
        if let physicsBody = SKPhysicsBody(circleOfRadius:myBall.size.width/1)
        {
            physicsBody.isDynamic = true
            physicsBody.affectedByGravity = true
            physicsBody.friction = 1
            physicsBody.restitution = 1
            physicsBody.mass = 0.0035744346678257 //<-- You really shouldnt mess with this unless you know what you are doing with mass
            myBall.physicsBody = physicsBody
        }
        addChild(myBall)

        myBall.physicsBody?.applyImpulse(CGVector(dx: 300.0, dy: -300.0))//<--this does not fore ??
    }
}