iOS UIViewController 和 Android Activity 生命周期對(duì)比

iOS和Android大體上的邏輯是相同的，細(xì)微上會(huì)有一些差別荤堪；

iOS UIViewController

• - (instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
• - (instancetype)init
• - (void)loadView;
• - (void)viewDidLoad;
• - (void)viewWillAppear:(BOOL)animated;
• - (void)viewDidAppear:(BOOL)animated;
• - (void)viewWillDisappear:(BOOL)animated;
• - (void)viewDidDisappear:(BOOL)animated;
• - (void)dealloc

打印如下:

-[MyViewController initWithNibName:bundle:]
-[MyViewController init]
-[MyViewController loadView]
-[MyViewController viewDidLoad]
-[MyViewController viewWillAppear:]
-[MyViewController viewDidAppear:]
-[MyViewController viewWillDisappear:]
-[MyViewController viewDidDisappear:]
-[MyViewController dealloc]

present方式

下面演示了從源控制器 OneViewController present 到目標(biāo)控制器 MyViewController 澄阳，再dismiss返回 OneViewController的過(guò)程

OneViewController 加載完成顯示順序:

-[OneViewController initWithNibName:bundle:]
-[OneViewController init]
-[OneViewController loadView]
-[OneViewController viewDidLoad]
-[OneViewController viewWillAppear:]
-[OneViewController viewDidAppear:]

從 OneViewController 通過(guò) present 方式到 MyViewController 過(guò)程如下:

-[MyViewController initWithNibName:bundle:]
-[MyViewController init]
-[MyViewController loadView]
-[MyViewController viewDidLoad]
-[OneViewController viewWillDisappear:]
-[MyViewController viewWillAppear:]
-[MyViewController viewDidAppear:]
-[OneViewController viewDidDisappear:]

可以看到需要等到目標(biāo)控制器完成 viewDidLoad 方法（即加載 view 完成）碎赢，源控制器才會(huì) Disappear速梗，目標(biāo)控制器 Appear

目標(biāo)控制器 dismiss 過(guò)程如下姻锁，即從目標(biāo)控制器返回到源控制器:

-[MyViewController viewWillDisappear:]
-[OneViewController viewWillAppear:]
-[OneViewController viewDidAppear:]
-[MyViewController viewDidDisappear:]
-[MyViewController dealloc]

可以看到，目標(biāo)控制器 WillDisappear 烁设，等到源控制器 viewDidAppear 了钓试，目標(biāo)控制器才會(huì)真正的 DidDisappear 和銷毀 dealloc

小結(jié)

• 同一個(gè)時(shí)刻弓熏，只有一個(gè)控制器 viewDidAppear ，只有一個(gè)控制器 viewDidAppear 另外一個(gè)控制器才會(huì) viewDidDisappear
• 一個(gè)控制器 A 的 viewWillDisappear 作為一個(gè)信號(hào)疚颊，另外一個(gè)控制器 B 才會(huì) viewWillAppear 和 viewDidAppear材义，控制器B viewDidAppear 作為信號(hào)，控制器 A 才會(huì) viewDidDisappear (可能還有 dealloc)

-[A viewWillDisappear:]
-[B viewWillAppear:]
-[B viewDidAppear:]
-[A viewDidDisappear:]
-[A dealloc]

navigation方式

下面演示了從源控制器 OneViewController 到目標(biāo)控制器 MyViewController 油挥，再返回 ViewController的過(guò)程

OneViewController控制器加載順序: 和 present方式相同

-[OneViewController initWithNibName:bundle:]
-[OneViewController init]
-[OneViewController loadView]
-[OneViewController viewDidLoad]
-[OneViewController viewWillAppear:]
-[OneViewController viewDidAppear:]

從 OneViewController push 到 MyViewController

-[MyViewController initWithNibName:bundle:]
-[MyViewController init]
-[MyViewController loadView]
-[MyViewController viewDidLoad]
-[OneViewController viewWillDisappear:]
-[MyViewController viewWillAppear:]
-[OneViewController viewDidDisappear:]
-[MyViewController viewDidAppear:]

從 MyViewController pop 到 OneViewController

-[MyViewController viewWillDisappear:]
-[OneViewController viewWillAppear:]
-[MyViewController viewDidDisappear:]
-[OneViewController viewDidAppear:]
-[MyViewController dealloc]

對(duì)比:

UIViewController生命周期對(duì)比.png

總結(jié)：

• 控制器A 切換到 到 控制器B 的大致順序?yàn)?
  • 1、[A viewWillDisappear]
  • 2惋鹅、[B viewWillAppear]
  • 3殉簸、[B viewDidAppear]
  • 4、[A viewDidDisappear]
• 如果是 present/dismiss 方式返十，順序?yàn)?1234
• 如果是 push/pop 方式椭微，順序?yàn)?code>1243

1蝇率、需要一個(gè)控制器 viewWillDisappear 作為信號(hào)刽沾，另外一個(gè)控制器開(kāi)會(huì)開(kāi)始處理侧漓；
2、控制器A到控制器B藤违，

• present/dismiss方式纵揍，需要 B viewDidAppear泽谨，然后A viewDidDisappear
• push/pop方式特漩，需要 A viewDidDisappear涂身，然后 B viewDidAppear

Android Activity

參考官方圖示

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activity 基本的四種狀態(tài)

• resumed : If an activity is in the foreground of the screen (at the top of the stack), it is active or running.
• paused: If an activity has lost focus but is still visible (that is, a new non-full-sized or transparent activity has focus on top of your activity), it is paused. A paused activity is completely alive (it maintains all state and member information and remains attached to the window manager), but can be killed by the system in extreme low memory situations.
• stopped: If an activity is completely obscured by another activity, it is stopped. It still retains all state and member information, however, it is no longer visible to the user so its window is hidden and it will often be killed by the system when memory is needed elsewhere.
• If an activity is paused or stopped, the system can drop the activity from memory by either asking it to finish, or simply killing its process. When it is displayed again to the user, it must be completely restarted and restored to its previous state.

下面為一開(kāi)始進(jìn)入MainActivity蛤售，跳轉(zhuǎn)到 LoginActivity陕凹，又返回到 MainActivity

// 1杜耙、MainActivity 創(chuàng)建
E/MainActivity: onCreate -- 
E/MainActivity: onStart -- 
E/MainActivity: onResume -- 

// 2、MainActivity 跳轉(zhuǎn)到 LoginActivity
E/MainActivity: onPause -- 
E/LoginActivity: onCreate -- 
E/LoginActivity: onStart -- 
E/LoginActivity: onResume -- 
E/MainActivity: onStop -- 

// 3记靡、LoginActivity 返回到 MainActivity
E/LoginActivity: onPause -- 
E/MainActivity: onRestart --
E/MainActivity: onStart -- 
E/MainActivity: onResume -- 
E/LoginActivity: onStop -- 
E/LoginActivity: onDestroy -- 

• onCreate() : activity 第一次被創(chuàng)建的時(shí)候摸吠，一般用作創(chuàng)建views嚎花、綁定數(shù)據(jù)紊选、獲取Bundle里面的數(shù)據(jù)等（頁(yè)面?zhèn)鬟f的數(shù)據(jù)）
  • 下一步: onStart()
• onRestart() : activity被stopped，然后又需要重新 onStart()献烦，看上面的例子
  • 下一步: onStart()
• onStart() : activity 變的對(duì)用戶可見(jiàn)visible
  • 下一步:
    • onResume() : activity 進(jìn)入前臺(tái) foreground
    • onStop() : activity 被隱藏了 hidden巩那，不可見(jiàn)了 (iOS沒(méi)有這個(gè)邏輯?)
• onResume() : activity 在 activity stack的最上面此蜈，可以和用戶進(jìn)行交互了；
  • 下一步 onPause()
• onPause() : 將要跳轉(zhuǎn)到另外一個(gè)activity令境，包含跳轉(zhuǎn)和返回
  • 下一步:
    • onResume() : 返回
    • onStop() : activity 被隱藏了 hidden顾瞪，不可見(jiàn)了 (iOS沒(méi)有這個(gè)邏輯?)
• onStop() : activity 對(duì)用戶不可見(jiàn)了；1瞧甩、開(kāi)啟了一個(gè)新的activity覆蓋在當(dāng)前的activity上面弥鹦；2彬坏、從當(dāng)前的activity返回到上一個(gè)activity
  • 下一步:
    • onRestart() : 類似 2 情況的 上一個(gè)activity
    • onDestroy() : 類似 2 情況的 當(dāng)前的activity
• onDestroy() : activity 被銷毀了，執(zhí)行 finish()

小結(jié)

頁(yè)面A 跳轉(zhuǎn)到 頁(yè)面B

• iOS : 頁(yè)面B 會(huì)走到 view加載完成方法 (viewDidLoad)务冕，然后頁(yè)面A才會(huì)將要消失(viewWillDisappear)
• Android : 然后頁(yè)面A才會(huì)將要消失(onPause)禀忆，然后才會(huì)走頁(yè)面B的方法

頁(yè)面B 跳轉(zhuǎn)到 頁(yè)面A類似

Android類似iOS的present方式跳轉(zhuǎn)頁(yè)面: 都是目標(biāo)控制器已經(jīng)顯示了，源控制器才會(huì)已經(jīng)消失了落恼；

Android比iOS多了一個(gè)onRestart()方法箩退，即重新啟動(dòng)