我已经在将碰撞处理封装到一个处理程序类中,这与在该示例代码中处理碰撞的方式非常相似.
在这个项目中,我找到了一个名为RPCollIDerType的结构的代码:
struct RPCollIDerType: OptionSetType,Hashable,CustomDeBUGStringConvertible { // MARK: Static propertIEs /// A dictionary to specify which `CollIDerType`s should be notifIEd of contacts with other `CollIDerType`s. static var requestedContactNotifications = [RPCollIDerType: [RPCollIDerType]]() /// A dictionary of which `CollIDerType`s should collIDe with other `CollIDerType`s. static var definedCollisions = [RPCollIDerType: [RPCollIDerType]]() // MARK: PropertIEs let rawValue: UInt32 // MARK: Options static var Obstacle: RPCollIDerType { return self.init(rawValue: 1 << 0) } static var PlayerBot: RPCollIDerType { return self.init(rawValue: 1 << 1) } static var TaskBot: RPCollIDerType { return self.init(rawValue: 1 << 2) } // MARK: Hashable var hashValue: Int { return Int(rawValue) } // MARK: SpriteKit Physics ConvenIEnce /// A value that can be assigned to a 'SKPhysicsBody`'s `categoryMask` property. var categoryMask: UInt32 { return rawValue } /// A value that can be assigned to a 'SKPhysicsBody`'s `collisionMask` property. var collisionMask: UInt32 { // Combine all of the collision requests for this type using a bitwise or. let mask = RPCollIDerType.definedCollisions[self]?.reduce(RPCollIDerType()) { initial,collIDerType in return initial.union(collIDerType) } // ProvIDe the rawValue of the resulting mask or 0 (so the object doesn't collIDe with anything). return mask?.rawValue ?? 0 } /// A value that can be assigned to a 'SKPhysicsBody`'s `contactMask` property. var contactMask: UInt32 { // Combine all of the contact requests for this type using a bitwise or. let mask = RPCollIDerType.requestedContactNotifications[self]?.reduce(RPCollIDerType()) { initial,collIDerType in return initial.union(collIDerType) } // ProvIDe the rawValue of the resulting mask or 0 (so the object doesn't need contact callbacks). return mask?.rawValue ?? 0 } // MARK: ContactNotifiableType ConvenIEnce /** Returns `true` if the `ContactNotifiableType` associated with this `CollIDerType` should be notifIEd of contact with the passed `CollIDerType`. */ func notifyOnContactWithCollIDerType(collIDerType: RPCollIDerType) -> Bool { if let requestedContacts = RPCollIDerType.requestedContactNotifications[self] { return requestedContacts.contains(collIDerType) } return false }}
每次设置SKPhysicsBody的.collisionBitmask / .contactBitmask / .categoryBitmask属性时都会使用此结构:(我已使用组件和实体设计指南实现了这一点)
class RPPhysicsComponent: GKComponent { var physicsBody: SKPhysicsBody init(physicsBody: SKPhysicsBody,collIDerType: RPCollIDerType) { self.physicsBody = physicsBody self.physicsBody.categoryBitMask = collIDerType.categoryMask self.physicsBody.collisionBitMask = collIDerType.collisionMask self.physicsBody.contactTestBitMask = collIDerType.contactMask }}
到现在为止还挺好.来自Objective-C我的问题是我不完全理解RPCollIDerType Struct之后的代码行:
/// A value that can be assigned to a 'SKPhysicsBody`'s `collisionMask` property.var collisionMask: UInt32 { // Combine all of the collision requests for this type using a bitwise or. let mask = RPCollIDerType.definedCollisions[self]?.reduce(RPCollIDerType()) { initial,collIDerType in return initial.union(collIDerType) } // ProvIDe the rawValue of the resulting mask or 0 (so the object doesn't collIDe with anything). return mask?.rawValue ?? 0}
这是否意味着每次我调用计算(这是他们在swift中调用的,对吧?)属性 – 当我将它分配给SKPhysicsBody时我会这样做 – 它将它添加到那些静态类词典中.但我在解释’mask’/’reduce’/’union’命令时遇到了问题.
这到底是做什么的?
解决方法 collisionMask是computed属性,它返回一个UInt32值,该值可以用作物理主体的碰撞位掩码.如果将计算属性分解为其功能部分,则更容易理解该计算属性的工作原理.但是首先,让我们添加一个PlayerBotBot应该与defineCollisions字典碰撞的RPCollIDerType对象数组:
RPCollIDerType.definedCollisions[.PlayerBot] = [.Obstacle,.TaskBot]
此时,definedCollisions字典包含一个单独的项目,其中PlayerBot和[.Obstacle,.TaskBot]分别作为键和值.可以把它想象成可以与PlayerBot碰撞的类别是Obstacle和TaskBot.
我们现在可以使用.PlayerBot从字典中检索值(即数组):
let array = RPCollIDerType.definedCollisions[.PlayerBot]
由于collisionMask是在RPCollIDerType中定义的,因此self用作字典键.此外,数组是可选的,因为对应于该键的值可能不存在于字典中.
然后,代码使用reduce方法将RPCollIDerType对象数组合成一个RPCollIDerType对象. reduce有两个参数:一个初始值(与数组元素的类型相同)和一个以值作为参数并返回值的函数(或闭包).在这种情况下,初始值是一个新的RPCollIDerType对象,闭包的参数和返回值也是RPCollIDerType对象:
array?.reduce(RPCollIDerType(),aFunction)
Apple的代码使用尾随闭包而不是传递函数来减少.从文档中,
If you need to pass a closure Expression to a function as the function’s final argument and the closure Expression@H_@R_403_6939@_67@ is long,it can be useful to write it as a trailing closure instead. A trailing closure is a closure Expression that is@H_@R_403_6939@_67@ written outsIDe of (and after) the parentheses of the function call it supports.
reduce迭代数组并使用初始值和每个数组元素作为参数调用闭包,返回的值用作下一次迭代的初始值:
let mask = array?.reduce(RPCollIDerType()) { initial,collIDerType in return initial.union(collIDerType)}
其中initial保持RPCollIDerType数组元素的中间并集,collIDerType是数组的当前元素.
此时,mask是一个RPCollIDerType对象,我们可以将其转换为UInt32
mask?.rawValue
这是collisionMask计算属性的返回值.
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