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。
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)。
下面是swift中扩展(Extensions)的说明
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。）
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。
同样是UIView类，我们分别看看oc和swift不同的实现方式。
1.我们先看看oc中的UIView
这是 UIView中的声明的代码
#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
其他的属性和方法都是使用分类的方式进行扩展的。
下面是页面渲染相关的属性和方法
@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
2.这是swift中的代码
UIView类中的声明
@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
}
页面渲染的代码
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()
}
3.创建我们自己的extension
下面就让我们尝试一下，写一个自己的swift分类
在get和set UIView的x和y属性的时候代码很繁琐，如下：
//get x
var x = self.view.frame.origin.x
//set x
var rect = self.view.frame
rect.origin.x = 100
self.view.frame = rect
我们希望这里的代码是这样的
//get x
var x = self.view.x
//set x
self.view.x = 100
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https://github.com/findM/UIView-Positioning
在swift中我们需要写一个extension来实现
3.1 新建swift文件
3.2 代码实现
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
}
全部的实现方法请参考这里https://github.com/findM/UIView-Positioning-Swift