消滅永生不死吸血鬼物件的 ARC

消滅永⽣生不死吸⾎血⿁鬼物件的
ARC
1
Swift Girls
彼得潘

彼得潘簡介
App程式設計入⾨門:iPhone.iPad
Swift程式設計入⾨門
正職: 作家
副業: 專欄欄作家，⼯工程師，講師，顧問，家教，App評審，
App接案，企業包班，創業家，iOS APP ⾦金金牌擺渡⼈人
iOS App⼯工程師/外包廠商的⾯面試鑑賞師，

相關教學資源
• FB粉絲團: 愛瘋⼀一切為蘋果的彼得潘 
http://www.facebook.com/iphone.peterpan
• 個⼈人網站 
http://apppeterpan.strikingly.com
• medium: 彼得潘的App Neverland 
https://medium.com/@apppeterpan
• GitBook: 彼得潘的iOS App開發便便利利貼 
https://www.gitbook.com/book/apppeterpan/iosappcodestickies/
• FB社團: 彼得潘的蘋果App開發教室 
https://www.facebook.com/groups/peterpanappclass/

相關教學資源
• 電⼦子報 
http://strikingly.us12.list-manage.com/subscribe?u=afa877b4a57124636b33826b0&id=4dd6b92dbb
• SlideShare 
http://www.slideshare.net/deeplovepan
• email: apppeterpan@gmail.com
• FB: https://www.facebook.com/deeplove.pan
• LINE: deeplovepeterpan

iOS的記憶體
• ⼩小⼩小的iPhone -> 少少的記憶體
• iPhone 7 plus: 3GB 
iMac: 32GB
• App執⾏行行時只能得到⼀一部分的記憶體，不
能獨佔所有的記憶體
5

物件和記憶體
• App執⾏行行時，產⽣生的⼀一個個物件，佔據著記憶體。
• 儲存屬性設定的資料
• 儲存⽅方法的程式碼
class Baby {
var age = 1
var name = "peter"
func eat() {
}
func sleep() {
}
}
6

指到物件的屬性
class Baby {
var age = 0
var myRabbit = Rabbit()
}
class Rabbit {
var age = 0
}
7

每個物件佔據不同⼤大⼩小的記憶體
class Baby {
var age = 0
var weight = 10
var height = 100
}
class Rabbit {
var age = 0
}
8

⼈人⼝口爆炸
正常⼈人只能活100歲
9

• 只會建立物件
• 不會殺死物件
• 超過系統允許使⽤用的記憶體上限
• App被強制終結⽣生命 -> crash
物件爆炸
10

memory leak
記憶體爆炸
永⽣生不死的物件
11
ex:漏⽔水

噬⾎血童話(美)
https://www.youtube.com/watch?v=0fLf64z0OKY
⾎血⾊色入侵(瑞典)
https://www.youtube.com/watch?v=FNsJH_TMN_Q
12

記憶體爆炸實例例
ViewController.swift
@IBAction func createBaby(sender: Any) {
for i in 0…1000000 {
let cuteBaby = Baby()
babyArray.append(cuteBaby)
}
}
13

記憶體爆炸實例例
實機測試，
模擬器記憶體充⾜足，
不易易測出
App Crash
2015-11-10 13:58:52.515 ArcDemo[751:222661] Received memory warning.
2015-11-10 13:58:52.516 ArcDemo[751:222661] Received memory warning.
Message from debugger: Terminated due to memory issue
14

偵測記憶體⽤用量量
15

偵測記憶體⽤用量量
• instrument的Activity Monitor
16

記憶體爆掉前的警告
UIViewController
func didReceiveMemoryWarning()
減少記憶體⽤用量量，比⽅方移除⽤用不到的view
17
UIApplicationDelegate
func applicationDidReceiveMemoryWarning(_ application:
UIApplication)

ARC
• Automatic Reference Counting
• ⾃自動追蹤reference物件的數字。當數字為0
時，物件即死亡
• 只作⽤用在物件，不會作⽤用在 struct & enum
(struct & enum 是 value type，是複製的概
念念）
18
https://www.raywenderlich.com/134411/arc-memory-management-swift

以是否還有⼈人關⼼心物件，
決定物件的⽣生死
cuteDog
handsomeDog
cuteDog 什什麼是reference ?
19
class Dog {
var name:String
init(name:String) {
self.name = name
}
}
var cuteDog:Dog? = Dog(name: "⼩小⽩白")
var handsomeDog = cuteDog
cuteDog = nil
handsomeDog = nil
變數儲存物件的記憶體位置

邁向死亡的最後⼀一哩路路deinit
Dog.swift
class Dog {
func eat() {
}
deinit {
print("主⼈人，我即將死去，謝謝你愛過我")
}
}
請在project測試，在 playground 不容易易測試
20

物件死亡
override func viewDidLoad() {
super.viewDidLoad()
var cuteDog:Dog? = Dog()
cuteDog?.eat()
print("史努比，我會養你⼀一輩⼦子的。")
cuteDog = nil
print("sorry，你我緣份已盡。")
}
21

兩兩個只能活⼀一個
super.viewDidLoad()
var cuteDog:Dog = Dog()
cuteDog.eat()
cuteDog = Dog()
print("sorry，我愛上了了另⼀一隻狗，你我緣份已盡。")
}
史努比，我會養你⼀一輩⼦子的。
主⼈人，我即將死去，謝謝你愛過我
sorry，我愛上了了另⼀一隻狗，你我緣份已盡。
22

function裡宣告的變數(常數) 
或function的參參數
test method執⾏行行完
後，變數cuteDog就⽤用不
到了了，因此也就沒有變
數指到⼩小狗物件。
func test() {
let cuteDog:Dog? = Dog()
cuteDog?.eat()
}
super.viewDidLoad()
self.test()
print("after test")
}
史努比，我會養你⼀一輩⼦子的。
主⼈人，我即將死去
after test
23
local 變數(常數)

類別的屬性
屬性將和類別建立的物件共存亡
super.viewDidLoad()
var cuteBaby:Baby = Baby()
}
class Baby {
var cuteDog = Dog()
deinit {
print("即將死去的寶寶")
}
}
Baby.swift
即將死去的寶寶
主⼈人，我即將死去
24

屬性將和類別建立的物件共存亡
25
cuteDog
cuteBaby

class Baby {
var name:String = "peter"
var cuteDog:Dog?
deinit {
print("baby (self.name) dead")
}
}
class Dog {
var name:String = ""
deinit {
print("dog (self.name) dead")
}
}
class ViewController: UIViewController {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
var cuteBaby1:Baby? = Baby()
cuteBaby1?.name = "andy"
cuteBaby1?.cuteDog = Dog()
cuteBaby1?.cuteDog?.name = "tony"
var cuteBaby2:Baby? = Baby()
cuteBaby2?.name = "jeff"
cuteBaby2?.cuteDog = cuteBaby1?.cuteDog
cuteBaby1 = nil
}
26
例例⼦子

全域變數(常數)
class ViewController: UIViewController {
唯有設為nil或改變它指向的⽬目標，
才能切斷他和物件的關聯聯
27

當物件被加到array或dictionary時，
也會增加reference
當物件存在array裡，
表⽰示物件
正被需要，關⼼心著
class ViewController: UIViewController,
UITextFieldDelegate {
var babyArray = [Baby]()
super.viewDidLoad()
let baby = Baby()
self.babyArray.append(baby)
}
28

當物件從array或dictionary移除時，
或是array或dictionary死亡時，
物件的reference將減少
class ViewController: UIViewController,
UITextFieldDelegate {
var babyArray = [Baby]()
super.viewDidLoad()
let baby = Baby()
self.babyArray.append(baby)
self.babyArray = []
}
29

reference cycle
class Baby {
var pet:Dog?
deinit {
print("⼈人⽣生⾃自古誰無死，留留取丹丹⼼心照汗青")
}
}
Baby.swift
Dog.swift
class Dog {
var owner:Baby?
deinit {
print("主⼈人，我即將死去，謝謝你愛過我")
}
} 30

reference cycle
super.viewDidLoad()
var cuteBaby:Baby? = Baby()
cuteDog?.owner = cuteBaby
cuteBaby?.pet = cuteDog
}
不死的⼈人和狗
31

reference cycle
32
pet
cuteBaby cuteDog
owner

Xcode 8 的
Memory Graph Debugger
33
https://developer.apple.com/library/content/documentation/DeveloperTools/Conceptual/debugging_with_xcode/chapters/special_debugging_workﬂows.html

Xcode 8 的
Memory Graph Debugger
34

記錄物件如何⽣生成 ?
35

找到不死的吸⾎血⿁鬼寶寶
36

利利⽤用weak解決cycle
Baby.swift
class Baby {
weak var pet:Dog?
deinit {
}
}
1. 不關⼼心物件，不會增加reference
2. 當物件死亡時，變數會被設成nil
37

38
pet
cuteBaby cuteDog
owner

super.viewDidLoad()
var cuteBaby:Baby? = Baby()
cuteDog?.owner = cuteBaby
cuteBaby?.pet = cuteDog
print("我親愛的(cuteBaby?.pet)")
cuteDog = nil
print("我親愛的(cuteBaby?.pet)")
}
我親愛的Optional(ArcDemo.Dog)
我親愛的nil
⼈人⽣生⾃自古誰無死，留留取丹丹⼼心照汗青
39
ex: 當埃及艷后死掉後，
忘記埃及艷后的名字，
才不會難過程式才不會危險

weak只能宣告optional的變數
40

利利⽤用unowned解決cycle
指到的物件死亡時，不會被⾃自動設為nil。
如果存取死亡物件將讓App crash
適合宣告非optional的變數(常數)
41

unowned
class Baby {
unowned var pet:Dog
init(pet:Dog) {
self.pet = pet
}
deinit {
}
}
Baby.swift
42

unowned
43
存取已經死掉的物件 -> 殭屍是很危險的

Address Sanitizer
讓程式停在有問題的程式碼
(存取有問題的記憶體)
44

closure的reference cycle
class Rabbit {
let name: String
var actionClosure: (() -> ())!
init(name: String) {
self.name = name
self.actionClosure = {
print("我是全天下最可愛的(self.name)")
}
}
func performAction() {
actionClosure()
}
deinit {
print("死了了都要愛")
}
}
Rabbit.swift
在closure裡存取外部物件，
因為之後可能會⽤用到物件，因此延長物件壽
命(增加它的reference)
45

closure的reference cycle
super.viewDidLoad()
var cuteRabbit:Rabbit? = Rabbit(name: "彼得兔")
}
cuteRabbit的actionClosure連結到兔⼦子物件，所以當cuteRabbit設為nil時，
仍然有reference，因此兔⼦子不會死
46

讓兔⼦子死掉的第⼀一種⽅方法
super.viewDidLoad()
var cuteRabbit:Rabbit? = Rabbit(name: "彼得兔")
cuteRabbit?.actionClosure = nil
}
八百萬種死法
常常忘記先將closure設為nil
closure不⾒見見得能設為nil，比⽅方它不是optional，
或者它是傳入function的參參數
47

capture list
self.name = name
self.actionClosure = { [unowned self] in
print("我是全天下最可愛的(self.name)")
}
}
Rabbit.swift
利利⽤用[ ]指定不關⼼心，不想增加reference的物件
利利⽤用unowned
[ ] 裡可有多個物件，以逗號分隔
48

capture list
self.name = name
self.actionClosure = { [weak self] in
if self != nil {
print("我是全天下最可愛的(self!.name)")
}
}
}
Rabbit.swift
weak將成為optional
49

當傳入function的參參數為closure時
若若此closure⽤用到某個物件，也會增加物件的reference
要等function執⾏行行完，物件的reference才會減少

super.viewDidLoad()
cuteBaby.name = "Jeff"
let urlStr = "https://res.cloudinary.com/hrscywv4p/image/upload/
c_limit,f_auto,h_3000,q_80,w_1200/v1/271374/http_s3.amazonaws.com_feather-files-
aviary-prod-us-
east-1_f5da8ea5e_2015-03-12_723490bbf79e44a788f5cd2516fefd46_myvzle.jpg"
let url = URL(string: urlStr)
let urlRequest = URLRequest(url: url!, cachePolicy:.returnCacheDataElseLoad,
timeoutInterval: 30)
let task = URLSession.shared.dataTask(with: urlRequest) {
(data:Data?, response:URLResponse?, err:Error?) -> Void in
print("cuteBaby in closure (cuteBaby)”)
}
task.resume()
print("viewDidLoad finish")
}
cuteBaby的reference count增加
viewDidLoad finish
cuteBaby in closure Test.Baby
baby Jeff dead

super.viewDidLoad()
cuteBaby.name = "Jeff"
aviary-prod-us-
let task = URLSession.shared.dataTask(with: urlRequest) { [weak cuteBaby]
print("cuteBaby in closure (cuteBaby)”)
}
task.resume()
}
cuteBaby的reference count不增加
viewDidLoad finish
baby Jeff dead
cuteBaby in closure nil

super.viewDidLoad()
aviary-prod-us-
let task = URLSession.shared.dataTask(with: urlRequest) { [weak self]
if let data = data {
self?.imageView.image = UIImage(data: data)
}
}
task.resume()
}
ex: controller download image
從 controller A 回到前⼀一⾴頁時， controller A 應該要⾺馬上死掉，
不該等圖片下載完才死掉

畫⾯面上的元件
當元件被加到view上時，表⽰示其正被需要，關⼼心著，不能死，所以會增加reference
當元件從view上移除，或是容納它的view死亡時，reference將減少
所以IBOutlet連結到程式時，預設是weak。
54

消滅永生不死吸血鬼物件的 ARC

Recommended

Recommended

More Related Content

More from 彼得潘 Pan

More from 彼得潘 Pan (15)

消滅永生不死吸血鬼物件的 ARC