<p>在oc中为了增强已有类的功能，我们经常使用分类。使用分类，我们可以在不破坏原有类的结构的前提下，对原有类进行模块化的扩展。</p>    <p>但是在swift中没有分类这种写法了。相对应的是swift中只有扩展( Extensions )。</p>    <p>下面是swift中扩展( Extensions )的说明</p>    <p>扩展就是向一个已有的类、结构体、枚举类型或者协议类型添加新功能（functionality）。这包括在没有权限获取原始源代码的情况下扩展类型的能力（即逆向建模）。扩展和 Objective-C 中的分类（categories）类似。（不过与 Objective-C 不同的是，Swift 的扩展没有名字。）</p>    <p>那么我们怎么在swift中实现oc中的分类呢？我们可以向苹果学习。</p>    <p>同样是UIView类，我们分别看看oc和swift不同的实现方式。</p>    <h3>1.我们先看看oc中的 UIView</h3>    <p>这是 UIView 中的声明的代码</p>    <pre>  <code class="language-swift">#ifndef SDK_HIDE_TIDE  NS_CLASS_AVAILABLE_IOS(2_0) @interface UIView : UIResponder <NSCoding, UIAppearance, UIAppearanceContainer, UIDynamicItem, UITraitEnvironment, UICoordinateSpace, UIFocusEnvironment>  #else  NS_CLASS_AVAILABLE_IOS(2_0) @interface UIView : UIResponder <NSCoding, UIAppearance, UIAppearanceContainer, UIDynamicItem, UITraitEnvironment, UICoordinateSpace>  #endif    + (Class)layerClass;                        // default is [CALayer class]. Used when creating the underlying layer for the view.    - (instancetype)initWithFrame:(CGRect)frame NS_DESIGNATED_INITIALIZER;  - (nullable instancetype)initWithCoder:(NSCoder *)aDecoder NS_DESIGNATED_INITIALIZER;    @property(nonatomic,getter=isUserInteractionEnabled) BOOL userInteractionEnabled;  // default is YES. if set to NO, user events (touch, keys) are ignored and removed from the event queue.  @property(nonatomic)                                 NSInteger tag;                // default is 0  @property(nonatomic,readonly,strong)                 CALayer  *layer;              // returns view's layer. Will always return a non-nil value. view is layer's delegate    #ifndef SDK_HIDE_TIDE  - (BOOL)canBecomeFocused NS_AVAILABLE_IOS(9_0); // NO by default  @property (readonly, nonatomic, getter=isFocused) BOOL focused NS_AVAILABLE_IOS(9_0);  #endif  + (UIUserInterfaceLayoutDirection)userInterfaceLayoutDirectionForSemanticContentAttribute:(UISemanticContentAttribute)attribute NS_AVAILABLE_IOS(9_0);  @property (nonatomic) UISemanticContentAttribute semanticContentAttribute NS_AVAILABLE_IOS(9_0);  @end</code></pre>    <p>其他的属性和方法都是使用分类的方式进行扩展的。</p>    <p>下面是页面渲染相关的属性和方法</p>    <pre>  <code class="language-swift">@interface UIView(UIViewRendering)    - (void)drawRect:(CGRect)rect;    - (void)setNeedsDisplay;  - (void)setNeedsDisplayInRect:(CGRect)rect;    @property(nonatomic)                 BOOL              clipsToBounds;              // When YES, content and subviews are clipped to the bounds of the view. Default is NO.  @property(nullable, nonatomic,copy)            UIColor          *backgroundColor UI_APPEARANCE_SELECTOR; // default is nil. Can be useful with the appearance proxy on custom UIView subclasses.  @property(nonatomic)                 CGFloat           alpha;                      // animatable. default is 1.0  @property(nonatomic,getter=isOpaque) BOOL              opaque;                     // default is YES. opaque views must fill their entire bounds or the results are undefined. the active CGContext in drawRect: will not have been cleared and may have non-zeroed pixels  @property(nonatomic)                 BOOL              clearsContextBeforeDrawing; // default is YES. ignored for opaque views. for non-opaque views causes the active CGContext in drawRect: to be pre-filled with transparent pixels  @property(nonatomic,getter=isHidden) BOOL              hidden;                     // default is NO. doesn't check superviews  @property(nonatomic)                 UIViewContentMode contentMode;                // default is UIViewContentModeScaleToFill  @property(nonatomic)                 CGRect            contentStretch NS_DEPRECATED_IOS(3_0,6_0) __TVOS_PROHIBITED; // animatable. default is unit rectangle {{0,0} {1,1}}. Now deprecated: please use -[UIImage resizableImageWithCapInsets:] to achieve the same effect.    @property(nullable, nonatomic,strong)          UIView           *maskView NS_AVAILABLE_IOS(8_0);    /*   -tintColor always returns a color. The color returned is the first non-default value in the receiver's superview chain (starting with itself).   If no non-default value is found, a system-defined color is returned.   If this view's -tintAdjustmentMode returns Dimmed, then the color that is returned for -tintColor will automatically be dimmed.   If your view subclass uses tintColor in its rendering, override -tintColorDidChange in order to refresh the rendering if the color changes.   */  @property(null_resettable, nonatomic, strong) UIColor *tintColor NS_AVAILABLE_IOS(7_0);    /*   -tintAdjustmentMode always returns either UIViewTintAdjustmentModeNormal or UIViewTintAdjustmentModeDimmed. The value returned is the first non-default value in the receiver's superview chain (starting with itself).   If no non-default value is found, UIViewTintAdjustmentModeNormal is returned.   When tintAdjustmentMode has a value of UIViewTintAdjustmentModeDimmed for a view, the color it returns from tintColor will be modified to give a dimmed appearance.   When the tintAdjustmentMode of a view changes (either the view's value changing or by one of its superview's values changing), -tintColorDidChange will be called to allow the view to refresh its rendering.   */  @property(nonatomic) UIViewTintAdjustmentMode tintAdjustmentMode NS_AVAILABLE_IOS(7_0);    /*   The -tintColorDidChange message is sent to appropriate subviews of a view when its tintColor is changed by client code or to subviews in the view hierarchy of a view whose tintColor is implicitly changed when its superview or tintAdjustmentMode changes.   */  - (void)tintColorDidChange NS_AVAILABLE_IOS(7_0);    @end</code></pre>    <h3>2.这是swift中的代码</h3>    <p>UIView类中的声明</p>    <pre>  <code class="language-swift">@available(iOS 2.0, *)      public class UIView : UIResponder, NSCoding, UIAppearance, UIAppearanceContainer, UIDynamicItem, UITraitEnvironment, UICoordinateSpace, UIFocusEnvironment {        public class func layerClass() -> AnyClass // default is [CALayer class]. Used when creating the underlying layer for the view.        public init(frame: CGRect)      public init?(coder aDecoder: NSCoder)        public var userInteractionEnabled: Bool // default is YES. if set to NO, user events (touch, keys) are ignored and removed from the event queue.      public var tag: Int // default is 0      public var layer: CALayer { get } // returns view's layer. Will always return a non-nil value. view is layer's delegate        @available(iOS 9.0, *)      public func canBecomeFocused() -> Bool // NO by default      @available(iOS 9.0, *)      public var focused: Bool { get }        @available(iOS 9.0, *)      public class func userInterfaceLayoutDirectionForSemanticContentAttribute(attribute: UISemanticContentAttribute) -> UIUserInterfaceLayoutDirection      @available(iOS 9.0, *)      public var semanticContentAttribute: UISemanticContentAttribute  }</code></pre>    <p>页面渲染的代码</p>    <pre>  <code class="language-swift">extension UIView {        public func drawRect(rect: CGRect)        public func setNeedsDisplay()      public func setNeedsDisplayInRect(rect: CGRect)        public var clipsToBounds: Bool // When YES, content and subviews are clipped to the bounds of the view. Default is NO.      @NSCopying public var backgroundColor: UIColor? // default is nil. Can be useful with the appearance proxy on custom UIView subclasses.      public var alpha: CGFloat // animatable. default is 1.0      public var opaque: Bool // default is YES. opaque views must fill their entire bounds or the results are undefined. the active CGContext in drawRect: will not have been cleared and may have non-zeroed pixels      public var clearsContextBeforeDrawing: Bool // default is YES. ignored for opaque views. for non-opaque views causes the active CGContext in drawRect: to be pre-filled with transparent pixels      public var hidden: Bool // default is NO. doesn't check superviews      public var contentMode: UIViewContentMode // default is UIViewContentModeScaleToFill      // animatable. default is unit rectangle {{0,0} {1,1}}. Now deprecated: please use -[UIImage resizableImageWithCapInsets:] to achieve the same effect.        @available(iOS 8.0, *)      public var maskView: UIView?        /*       -tintColor always returns a color. The color returned is the first non-default value in the receiver's superview chain (starting with itself).       If no non-default value is found, a system-defined color is returned.       If this view's -tintAdjustmentMode returns Dimmed, then the color that is returned for -tintColor will automatically be dimmed.       If your view subclass uses tintColor in its rendering, override -tintColorDidChange in order to refresh the rendering if the color changes.       */      @available(iOS 7.0, *)      public var tintColor: UIColor!        /*       -tintAdjustmentMode always returns either UIViewTintAdjustmentModeNormal or UIViewTintAdjustmentModeDimmed. The value returned is the first non-default value in the receiver's superview chain (starting with itself).       If no non-default value is found, UIViewTintAdjustmentModeNormal is returned.       When tintAdjustmentMode has a value of UIViewTintAdjustmentModeDimmed for a view, the color it returns from tintColor will be modified to give a dimmed appearance.       When the tintAdjustmentMode of a view changes (either the view's value changing or by one of its superview's values changing), -tintColorDidChange will be called to allow the view to refresh its rendering.       */      @available(iOS 7.0, *)      public var tintAdjustmentMode: UIViewTintAdjustmentMode        /*       The -tintColorDidChange message is sent to appropriate subviews of a view when its tintColor is changed by client code or to subviews in the view hierarchy of a view whose tintColor is implicitly changed when its superview or tintAdjustmentMode changes.       */      @available(iOS 7.0, *)      public func tintColorDidChange()  }</code></pre>    <h3>3.创建我们自己的extension</h3>    <p>下面就让我们尝试一下，写一个自己的swift分类</p>    <p>在get和set UIView 的x和y属性的时候代码很繁琐，如下：</p>    <pre>  <code class="language-swift">//get x  var x = self.view.frame.origin.x    //set x  var rect = self.view.frame  rect.origin.x = 100  self.view.frame = rect</code></pre>    <p>我们希望这里的代码是这样的</p>    <pre>  <code class="language-swift">//get x  var x = self.view.x  //set x  self.view.x = 100</code></pre>    <p>在oc中我们可以写一个分类来实现，这个难度不大。懒的自己写的可以参照这个 <a href="/misc/goto?guid=4959731214079769712" rel="nofollow,noindex">https://github.com/findM/UIView-Positioning</a></p>    <p>在swift中我们需要写一个extension来实现</p>    <p>3.1 新建swift文件</p>    <p style="text-align:center"><img src="https://simg.open-open.com/show/2b7d4d1a76dffd1dc12e7172ecbefa51.png"></p>    <p style="text-align:center">新建swift文件.png</p>    <p>3.2 代码实现</p>    <pre>  <code class="language-swift">import Foundation  import UIKit    //private var PERSON_ID_NUMBER_PROPERTY = 0    extension UIView {      public var x: CGFloat{          get{              return self.frame.origin.x          }          set{              var r = self.frame              r.origin.x = newValue              self.frame = r          }      }      public var y: CGFloat{          get{              return self.frame.origin.y          }          set{              var r = self.frame              r.origin.y = newValue              self.frame = r          }      }      //其他的篇幅原因就不在这里一一实现了  }</code></pre>    <p> </p>    <p>来自：http://www.jianshu.com/p/0176efcc5e56</p>    <p> </p>