Swift 实现一个兼容iOS、tvOS、OSX的抽象层

级别： ★☆☆☆☆
标签：「iOS」「Swift」「抽象层」
作者： dac_1033
审校： QiShare团队

有时开发一个工具包或者一个framework时，会要求兼容iOS、tvOS、OSX等苹果相关的平台，这些平台里的库、类及方法的名字和功能都很相近，如果想封装一套代码可以同时运行在三个平台上，那么就需要对相关的库、类及方法进行一个简单的抽象。在git上学习三方库源码的过程中，遇到过类似的实现，大致的抽象过程实现如下：

import Foundation

#if os(iOS) || os(tvOS)

import UIKit

    // MARK: - 关于类型

    public typealias NSUIScreen = UIScreen

    public typealias NSUIFont = UIFont
    public typealias NSUIColor = UIColor
    public typealias NSUIEvent = UIEvent
    public typealias NSUITouch = UITouch
    public typealias NSUIImage = UIImage

    public typealias NSUIGestureRecognizer = UIGestureRecognizer
    public typealias NSUIGestureRecognizerState = UIGestureRecognizer.State
    public typealias NSUIGestureRecognizerDelegate = UIGestureRecognizerDelegate
    public typealias NSUITapGestureRecognizer = UITapGestureRecognizer
    public typealias NSUIPanGestureRecognizer = UIPanGestureRecognizer

#if !os(tvOS)
    public typealias NSUIPinchGestureRecognizer = UIPinchGestureRecognizer
    public typealias NSUIRotationGestureRecognizer = UIRotationGestureRecognizer
#endif
    
    public typealias NSUIDisplayLink = CADisplayLink


    // MARK: - 关于类型方法扩展

    extension NSUITapGestureRecognizer {
        
        @objc final func nsuiNumberOfTouches() -> Int {
            return numberOfTouches
        }
        
        @objc final var nsuiNumberOfTapsRequired: Int {
            get {
                return self.numberOfTapsRequired
            }
            set {
                self.numberOfTapsRequired = newValue
            }
        }
    }
    
    extension NSUIPanGestureRecognizer {
        
        @objc final func nsuiNumberOfTouches() -> Int {
            return numberOfTouches
        }
        
        @objc final func nsuiLocationOfTouch(_ touch: Int, inView: UIView?) -> CGPoint {
            return super.location(ofTouch: touch, in: inView)
        }
    }
    
#if !os(tvOS)
    extension NSUIRotationGestureRecognizer
    {
        @objc final var nsuiRotation: CGFloat
        {
            get { return rotation }
            set { rotation = newValue }
        }
    }
#endif
    
#if !os(tvOS)
    extension NSUIPinchGestureRecognizer
    {
        @objc final var nsuiScale: CGFloat
        {
            get
            {
                return scale
            }
            set
            {
                scale = newValue
            }
        }
        
        @objc final func nsuiLocationOfTouch(_ touch: Int, inView: UIView?) -> CGPoint
        {
            return super.location(ofTouch: touch, in: inView)
        }
    }
#endif

    extension UIView
    {
        @objc final var nsuiGestureRecognizers: [NSUIGestureRecognizer]?
        {
            return self.gestureRecognizers
        }
    }
    
    extension UIScreen
    {
        @objc final var nsuiScale: CGFloat
        {
            return self.scale
        }
    }


    // MARK: - 定义新类NSUIView

    open class NSUIView: UIView
    {
        public final override func touchesBegan(_ touches: Set<NSUITouch>, with event: NSUIEvent?)
        {
            self.nsuiTouchesBegan(touches, withEvent: event)
        }

        public final override func touchesMoved(_ touches: Set<NSUITouch>, with event: NSUIEvent?)
        {
            self.nsuiTouchesMoved(touches, withEvent: event)
        }

        public final override func touchesEnded(_ touches: Set<NSUITouch>, with event: NSUIEvent?)
        {
            self.nsuiTouchesEnded(touches, withEvent: event)
        }

        public final override func touchesCancelled(_ touches: Set<NSUITouch>, with event: NSUIEvent?)
        {
            self.nsuiTouchesCancelled(touches, withEvent: event)
        }

        @objc open func nsuiTouchesBegan(_ touches: Set<NSUITouch>, withEvent event: NSUIEvent?)
        {
            super.touchesBegan(touches, with: event!)
        }

        @objc open func nsuiTouchesMoved(_ touches: Set<NSUITouch>, withEvent event: NSUIEvent?)
        {
            super.touchesMoved(touches, with: event!)
        }

        @objc open func nsuiTouchesEnded(_ touches: Set<NSUITouch>, withEvent event: NSUIEvent?)
        {
            super.touchesEnded(touches, with: event!)
        }

        @objc open func nsuiTouchesCancelled(_ touches: Set<NSUITouch>?, withEvent event: NSUIEvent?)
        {
            super.touchesCancelled(touches!, with: event!)
        }

        @objc var nsuiLayer: CALayer?
        {
            return self.layer
        }
    }

#endif


#if os(OSX)
    import Cocoa
    import Quartz

  public typealias NSUIScreen = NSScreen
    
    public typealias NSUIFont = NSFont
    public typealias NSUIColor = NSColor
    public typealias NSUIEvent = NSEvent
    public typealias NSUITouch = NSTouch
    
    public typealias NSUIGestureRecognizer = NSGestureRecognizer
    public typealias NSUIGestureRecognizerState = NSGestureRecognizer.State
    public typealias NSUIGestureRecognizerDelegate = NSGestureRecognizerDelegate
    public typealias NSUITapGestureRecognizer = NSClickGestureRecognizer
    public typealias NSUIPanGestureRecognizer = NSPanGestureRecognizer
    public typealias NSUIPinchGestureRecognizer = NSMagnificationGestureRecognizer
    public typealias NSUIRotationGestureRecognizer = NSRotationGestureRecognizer
    
    
    public class NSUIDisplayLink
    {
        private var timer: Timer?
        private var displayLink: CVDisplayLink?
        private var _timestamp: CFTimeInterval = 0.0
        
        private weak var _target: AnyObject?
        private var _selector: Selector
        
        public var timestamp: CFTimeInterval
        {
            return _timestamp
        }

        init(target: AnyObject, selector: Selector)
        {
            _target = target
            _selector = selector
            
            if CVDisplayLinkCreateWithActiveCGDisplays(&displayLink) == kCVReturnSuccess
            {
                
                CVDisplayLinkSetOutputCallback(displayLink!, { (displayLink, inNow, inOutputTime, flagsIn, flagsOut, userData) -> CVReturn in
                    
                    let _self = unsafeBitCast(userData, to: NSUIDisplayLink.self)
                    
                    _self._timestamp = CFAbsoluteTimeGetCurrent()
                    _self._target?.performSelector(onMainThread: _self._selector, with: _self, waitUntilDone: false)
                    
                    return kCVReturnSuccess
                    }, Unmanaged.passUnretained(self).toOpaque())
            }
            else
            {
                timer = Timer(timeInterval: 1.0 / 60.0, target: target, selector: selector, userInfo: nil, repeats: true)
            }
        }
        
        deinit
        {
            stop()
        }

        open func add(to runloop: RunLoop, forMode mode: RunLoopMode)
        {
            if displayLink != nil
            {
                CVDisplayLinkStart(displayLink!)
            }
            else if timer != nil
            {
                runloop.add(timer!, forMode: mode)
            }
        }

        open func remove(from: RunLoop, forMode: RunLoopMode)
        {
            stop()
        }
        
        private func stop()
        {
            if displayLink != nil
            {
                CVDisplayLinkStop(displayLink!)
            }
            if timer != nil
            {
                timer?.invalidate()
            }
        }
    }
    
    
    extension NSUITapGestureRecognizer
    {
        final func nsuiNumberOfTouches() -> Int
        {
            return 1
        }
        
        final var nsuiNumberOfTapsRequired: Int
        {
            get
            {
                return self.numberOfClicksRequired
            }
            set
            {
                self.numberOfClicksRequired = newValue
            }
        }
    }

    extension NSUIPanGestureRecognizer
    {
        final func nsuiNumberOfTouches() -> Int
        {
            return 1
        }
        
        /// FIXME: Currently there are no more than 1 touch in OSX gestures, and not way to create custom touch gestures.
        final func nsuiLocationOfTouch(_ touch: Int, inView: NSView?) -> NSPoint
        {
            return super.location(in: inView)
        }
    }
    
    extension NSUIRotationGestureRecognizer
    {
        /// FIXME: Currently there are no velocities in OSX gestures, and not way to create custom touch gestures.
        final var velocity: CGFloat
        {
            return 0.1
        }
        
        final var nsuiRotation: CGFloat
        {
            get { return -rotation }
            set { rotation = -newValue }
        }
    }
    
    extension NSUIPinchGestureRecognizer
    {
        final var nsuiScale: CGFloat
        {
            get
            {
                return magnification + 1.0
            }
            set
            {
                magnification = newValue - 1.0
            }
        }
        
        /// FIXME: Currently there are no more than 1 touch in OSX gestures, and not way to create custom touch gestures.
        final func nsuiLocationOfTouch(_ touch: Int, inView view: NSView?) -> NSPoint
        {
            return super.location(in: view)
        }
    }

    extension NSView
    {
        final var nsuiGestureRecognizers: [NSGestureRecognizer]?
        {
            return self.gestureRecognizers
        }
    }
    
    extension NSScreen
    {
        final var nsuiScale: CGFloat
        {
            return self.backingScaleFactor
        }
    }
    
    
    open class NSUIView: NSView
    {
        public final override var isFlipped: Bool
        {
            return true
        }

        func setNeedsDisplay()
        {
            self.setNeedsDisplay(self.bounds)
        }

        
        public final override func touchesBegan(with event: NSEvent)
        {
            self.nsuiTouchesBegan(event.touches(matching: .any, in: self), withEvent: event)
        }

        public final override func touchesEnded(with event: NSEvent)
        {
            self.nsuiTouchesEnded(event.touches(matching: .any, in: self), withEvent: event)
        }

        public final override func touchesMoved(with event: NSEvent)
        {
            self.nsuiTouchesMoved(event.touches(matching: .any, in: self), withEvent: event)
        }

        open override func touchesCancelled(with event: NSEvent)
        {
            self.nsuiTouchesCancelled(event.touches(matching: .any, in: self), withEvent: event)
        }

        open func nsuiTouchesBegan(_ touches: Set<NSUITouch>, withEvent event: NSUIEvent?)
        {
            super.touchesBegan(with: event!)
        }

        open func nsuiTouchesMoved(_ touches: Set<NSUITouch>, withEvent event: NSUIEvent?)
        {
            super.touchesMoved(with: event!)
        }

        open func nsuiTouchesEnded(_ touches: Set<NSUITouch>, withEvent event: NSUIEvent?)
        {
            super.touchesEnded(with: event!)
        }

        open func nsuiTouchesCancelled(_ touches: Set<NSUITouch>?, withEvent event: NSUIEvent?)
        {
            super.touchesCancelled(with: event!)
        }
        
        open var backgroundColor: NSUIColor?
        {
            get
            {
                return self.layer?.backgroundColor == nil
                    ? nil
                    : NSColor(cgColor: self.layer!.backgroundColor!)
            }
            set
            {
                self.wantsLayer = true
                self.layer?.backgroundColor = newValue == nil ? nil : newValue!.cgColor
            }
        }

        final var nsuiLayer: CALayer?
        {
            return self.layer
        }
    }
    
#endif

1. 用宏定义 #if 来判断os(iOS)、os(tvOS)、os(OSX)，以区分不同平台；
2. 在swift中，可以用typealias对不同平台上的类型起同样的别名，如NSUIFont作为别名分别对应UIFont和NSFont；
3. 在swift中，可以用 extension 扩展类的方法以达到在不同平台上，类中方法同名的目的。例如在使用platform这个类的地方，调用NSUIScreen. nsuiScale;
4. 在上述代码中，os(OSX)平台上没有的UIDisplayLink对应的雷，但是代码中全新定义了一个NSUIDisplayLink，NSUIDisplayLink中的方法也与UIDisplayLink中相应方法同名。

这样，一个简单的跨平台抽象层就可以使用了，在需要这个platform时，如果你的代码里还用到其他夸端使用的类型，加载platform里就可以了。

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