继承

13 继承.playground/Contents.swift

@@ -1,3 +1,72 @@
 import UIKit
 
-var greeting = "Hello, playground"
+//class Animal {
+//    func speak() {
+//        print("Animal speak")
+//    }
+//    subscript(index: Int) -> Int {
+//        return index
+//    }
+//}
+//
+//var anim: Animal
+//anim = Animal()
+//anim.speak()
+//print(anim[6])
+//
+//class Cat: Animal {
+//    override func speak() {
+//        print("Cat speak")
+//    }
+//
+//    override subscript(index: Int) -> Int {
+//        return super[index] + 1
+//    }
+//}
+//
+//var cat = Cat()
+//cat.speak()
+//print(cat[6])
+
+class Animal {
+    class func speak() {
+        print("Animal speak")
+    }
+    static subscript(index: Int) -> Int {
+        return index
+    }
+}
+
+class Cat: Animal {
+    override class func speak() {
+        super.speak()
+        print("Cat speak")
+    }
+}
+
+class Circle {
+    static var radius: Int = 0
+    class var diameter: Int {
+        set {
+            print("Circle setDiameter")
+            radius = newValue / 2
+        }
+        get {
+            print("Circle getDiameter")
+            return radius * 2
+        }
+    }
+}
+
+class SubCircle: Circle {
+    override class var diameter: Int {
+        set {
+            print("SubCircle setDiameter")
+            super.diameter = newValue > 0 ? newValue : 0
+        }
+        get {
+            print("SubCircle getDiameter")
+            return super.diameter
+        }
+    }
+}

13 继承.playground/Resources/README.md

@@ -0,0 +1,225 @@
+### 继承（Inheritance）
+
+值类型（枚举、结构体）不支持继承，只有类支持继承。
+
+* 没有父类的类称为基类
+* 子类可以重写父类的**下标**、**方法**、**属性**，重写必须加上 `override` 关键字
+
+#### 重写实例方法、下标
+
+```swift
+class Animal {
+    func speak() {
+        print("Animal speak")
+    }
+    subscript(index: Int) -> Int {
+        return index
+    }
+}
+
+var anim: Animal
+anim = Animal()
+// Animal speak
+anim.speak()
+// 6
+print(anim[6])
+
+class Cat: Animal {
+    override func speak() {
+        super.speak()
+        print("Cat speak")
+    }
+    
+    override subscript(index: Int) -> Int {
+        return super[index] + 1
+    }
+}
+
+var cat = Cat()
+// Animal speak
+// Cat speak
+cat.speak()
+// 7
+print(cat[6])
+```
+
+#### 重写类型方法、下标
+
+* 被 `class` 修饰的类型方法、下标，允许被子类重写
+* 被 `static` 修饰的类型方法、下标，不允许被子类重写
+
+```swift
+class Animal {
+    // class 修饰的方法可以子类被重写
+    class func speak() {
+        print("Animal speak")
+    }
+    // static 修饰的方法不可以子类被重写
+    static subscript(index: Int) -> Int {
+        return index
+    }
+}
+
+class Cat: Animal {
+    override class func speak() {
+        super.speak()
+        print("Cat speak")
+    }
+}
+```
+
+
+
+#### 重写属性
+
+1. 子类可以将父类的属性（存储、计算）重写为 **计算属性**。
+2. 子类不可以将父类属性重写为 **存储属性**
+3. 只能重写 `var` 属性，不能重写 `let` 属性
+4. 重写时，属性名、类型要一致
+5. 子类重写后的属性权限 **不能小于** 父类属性的权限
+   1. 如果父类属性是只读，那么子类重写后的属性可以是只读的，也可以是可读写的
+   2. 如果父类是可读写的，那么子类重写后的属性也必须是可读写的
+
+##### 重写实例属性
+
+```swift
+class SubCircle : Circle { 
+	override var radius: Int {
+		set {
+			print("SubCircle setRadius")
+			super.radius = newValue > 0 ? newValue : 0 
+		}
+		get {
+			print("SubCircle getRadius") 
+			return super.radius
+		} 
+	}
+	override var diameter: Int { 
+		set {
+			print("SubCircle setDiameter")
+			super.diameter = newValue > 0 ? newValue : 0 
+		}
+		get {
+			print("SubCircle getDiameter") 
+			return super.diameter
+		} 
+	}
+}
+
+circle = SubCircle() 
+// SubCircle setRadius
+circle.radius = 6
+// SubCircle getDiameter 
+// Circle getDiameter 
+// SubCircle getRadius 
+// 12
+print(circle.diameter) 
+// SubCircle setDiameter
+// Circle setDiameter 
+// SubCircle setRadius 
+circle.diameter = 20
+// SubCircle getRadius 
+// 10
+print(circle.radius)
+```
+
+##### 重写类型属性
+
+1. 被 `class` 修饰的计算类型属性，可以被子类重写
+
+2. 被 `static` 修饰的类型属性（存储、计算），不可以被子类重写
+
+```swift
+class Circle {
+    static var radius: Int = 0
+    class var diameter: Int {
+        set {
+            print("Circle setDiameter")
+            radius = newValue / 2
+        }
+        get {
+            print("Circle getDiameter")
+            return radius * 2
+        }
+    }
+}
+
+class SubCircle: Circle {
+    override class var diameter: Int {
+        set {
+            print("SubCircle setDiameter")
+            super.diameter = newValue > 0 ? newValue : 0
+        }
+        get {
+            print("SubCircle getDiameter")
+            return super.diameter
+        }
+    }
+}
+```
+
+#### 属性观察器
+
+可以在子类中为父类属性（除了只读计算属性、let属性）增加属性观察器
+
+```swift
+class Circle {
+  // 父类是存储属性
+	var radius: Int = 1 
+}
+
+class SubCircle : Circle { 
+	override var radius: Int {
+		willSet {
+			print("SubCircle willSetRadius", newValue) 
+		}
+		didSet {
+			print("SubCircle didSetRadius", oldValue, radius)
+		} 
+	}
+}
+var circle = SubCircle()
+// SubCircle willSetRadius 10 
+// SubCircle didSetRadius 1 10 
+circle.radius = 10
+```
+
+```swift
+class Circle {
+  // 父类存储属性也有属性观察器
+	var radius: Int = 1 { 
+		willSet {
+			print("Circle willSetRadius", newValue) 
+		}
+		didSet {
+			print("Circle didSetRadius", oldValue, radius) 
+		}
+	} 
+}
+
+class SubCircle : Circle { 
+	override var radius: Int {
+		willSet {
+			print("SubCircle willSetRadius", newValue) 
+		}
+		didSet {
+			print("SubCircle didSetRadius", oldValue, radius)
+		}
+	}
+}
+
+var circle = SubCircle()
+// SubCircle willSetRadius 10 
+// Circle willSetRadius 10 
+// Circle didSetRadius 1 10 
+// SubCircle didSetRadius 1 10 
+circle.radius = 10
+```
+
+
+
+#### final
+
+被 `final` 修饰的方法、下标、属性，禁止被重写
+
+被 `final` 修饰的类，禁止被继承

13 继承.playground/contents.xcplayground

@@ -1,4 +1,4 @@
 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
-<playground version='5.0' target-platform='ios' buildActiveScheme='true' executeOnSourceChanges='false' importAppTypes='true'>
+<playground version='5.0' target-platform='ios' buildActiveScheme='true' importAppTypes='true'>
     <timeline fileName='timeline.xctimeline'/>
 </playground>

13 继承.playground/timeline.xctimeline

@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<Timeline
-   version = "3.0">
-   <TimelineItems>
-   </TimelineItems>
-</Timeline>

13 继承.playground/xcuserdata/jiulinxiri.xcuserdatad/xcschemes/xcschememanagement.plist

@@ -1,16 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
-<plist version="1.0">
-<dict>
-	<key>SchemeUserState</key>
-	<dict>
-		<key>13 继承 (Playground).xcscheme</key>
-		<dict>
-			<key>isShown</key>
-			<false/>
-			<key>orderHint</key>
-			<integer>0</integer>
-		</dict>
-	</dict>
-</dict>
-</plist>