轉載請注明出處：http://www.lxweimin.com/p/1449e3ec2720
生命周期是個老生常談的問題了，今天做個匯總，全當是記個筆記，以后查找起來方便一些。下面我將分三個部分來介紹。
為了演示方便我創建了兩個Activity：ActivityA ActivityB
除生命周期函數之外也包含了onSaveInstanceState、onRestoreInstanceState、onNewIntent、onConfigurationChanged的回調
1. 特殊場景下的生命周期
1.1 按電源鍵關屏
01-18 23:16:21.003 7037-7037/com.landptf.blog E/ActivityA: onPause()
01-18 23:16:21.033 7037-7037/com.landptf.blog E/ActivityA: onSaveInstanceState()
01-18 23:16:21.033 7037-7037/com.landptf.blog E/ActivityA: onStop()
1.2 按Home鍵回到主界面
01-18 23:18:46.413 7037-7037/com.landptf.blog E/ActivityA: onPause()
01-18 23:18:46.693 7037-7037/com.landptf.blog E/ActivityA: onSaveInstanceState()
01-18 23:18:46.693 7037-7037/com.landptf.blog E/ActivityA: onStop()
1.3 按菜單鍵或長按Home鍵查看后臺程序列表
01-18 23:19:50.093 7037-7037/com.landptf.blog E/ActivityA: onPause()
01-18 23:19:50.173 7037-7037/com.landptf.blog E/ActivityA: onSaveInstanceState()
01-18 23:19:50.173 7037-7037/com.landptf.blog E/ActivityA: onStop()
1.4 Android 7.0 分屏相關
長按后分屏將分別執行
01-18 10:36:50.950 1453-1453/com.landptf.blog E/ActivityA: onDestroy()
01-18 10:36:50.954 1453-1453/com.landptf.blog E/ActivityA: onCreate()
01-18 10:36:50.961 1453-1453/com.landptf.blog E/ActivityA: onStart()
01-18 10:36:50.961 1453-1453/com.landptf.blog E/ActivityA: onRestoreInstanceState()
01-18 10:36:50.962 1453-1453/com.landptf.blog E/ActivityA: onResume()
01-18 10:36:50.962 1453-1453/com.landptf.blog E/ActivityA: onPause()
01-18 10:36:50.995 1453-1453/com.landptf.blog E/ActivityA: onResume()
01-18 10:36:51.831 1453-1453/com.landptf.blog E/ActivityA: onPause()
01-18 10:36:54.355 1453-1453/com.landptf.blog E/ActivityA: onResume()
從log中可以看出，activity先銷毀之后重建，并且執行兩次焦點切換事件
然后反復點擊屏幕上的兩個應用焦點將來回切換
01-18 10:39:26.193 1453-1453/com.landptf.blog E/ActivityA: onPause()
01-18 10:39:28.400 1453-1453/com.landptf.blog E/ActivityA: onResume()
01-18 10:39:29.534 1453-1453/com.landptf.blog E/ActivityA: onPause()
01-18 10:39:30.437 1453-1453/com.landptf.blog E/ActivityA: onResume()
注：如果是視頻類應用不可以在onPause()方法里暫停
1.5 屏幕旋轉
- 切橫屏
01-18 10:44:27.840 1453-1453/com.landptf.blog E/ActivityA: onPause()
01-18 10:44:27.841 1453-1453/com.landptf.blog E/ActivityA: onSaveInstanceState()
01-18 10:44:27.859 1453-1453/com.landptf.blog E/ActivityA: onStop()
01-18 10:44:27.860 1453-1453/com.landptf.blog E/ActivityA: onDestroy()
01-18 10:44:27.871 1453-1453/com.landptf.blog E/ActivityA: onCreate()
01-18 10:44:27.877 1453-1453/com.landptf.blog E/ActivityA: onStart()
01-18 10:44:27.878 1453-1453/com.landptf.blog E/ActivityA: onRestoreInstanceState()
01-18 10:44:27.879 1453-1453/com.landptf.blog E/ActivityA: onResume()
Activity重建
- 切豎屏
同上 與切橫屏時完全相同的生命周期 - 設置config為orientation|keyboardHidden|screenSize后切橫豎屏
android:configChanges="orientation|keyboardHidden|screenSize"
01-18 11:15:50.523 30577-30577/com.landptf.blog E/ActivityA: onConfigurationChanged()
1.6 內存不足導致被系統回收
當內存不足時會優先將處于后臺的Activity回收，ActivityA在后臺，ActivityB在前臺時，若ActivityA被回收后按Back鍵返回到ActivityA時，ActivityA會重建，執行過程如下：
01-18 10:36:50.954 1453-1453/com.landptf.blog E/ActivityA: onCreate()
01-18 10:36:50.961 1453-1453/com.landptf.blog E/ActivityA: onStart()
01-18 10:36:50.961 1453-1453/com.landptf.blog E/ActivityA: onRestoreInstanceState()
01-18 10:36:50.962 1453-1453/com.landptf.blog E/ActivityA: onResume()
1.7 新Activity未完全遮擋舊Activity時的生命周期
- 設置ActivityB的theme為
android:theme="@style/Theme.AppCompat.Dialog"
01-18 11:29:05.977 10621-10621/com.landptf.blog E/ActivityA: onPause()
01-18 11:29:05.980 10621-10621/com.landptf.blog E/ActivityB: onCreate()
01-18 11:29:05.983 10621-10621/com.landptf.blog E/ActivityB: onStart()
01-18 11:29:05.983 10621-10621/com.landptf.blog E/ActivityB: onResume()
- 在ActivityB的onCreate()方法中添加
getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
使其背景透明，此時從A啟動B，生命周期如下：
01-18 11:41:12.200 22238-22238/com.landptf.blog E/ActivityA: onPause()
01-18 11:41:12.202 22238-22238/com.landptf.blog E/ActivityB: onCreate()
01-18 11:41:12.207 22238-22238/com.landptf.blog E/ActivityB: onStart()
01-18 11:41:12.208 22238-22238/com.landptf.blog E/ActivityB: onResume()
可以看到兩種方式的生命周期完全相同，都不會執行ActivityA的onStop()方法
2. 與啟動模式相關的生命周期
該博客內容重點不在于講解Activity的啟動模式，有興趣的同學可以自行學習
- singleTop
設置ActivityA的launchMode為singleTop，首次啟動ActivityA會執行
01-19 09:58:16.175 11336-11336/com.landptf.blog E/ActivityA: onCreate()
01-19 09:58:16.179 11336-11336/com.landptf.blog E/ActivityA: onStart()
01-19 09:58:16.179 11336-11336/com.landptf.blog E/ActivityA: onResume()
當ActivityA處于棧頂時，再次打開ActivityA后，會執行
01-19 09:58:18.903 11336-11336/com.landptf.blog E/ActivityA: onPause()
01-19 09:58:18.903 11336-11336/com.landptf.blog E/ActivityA: onNewIntent()
01-19 09:58:18.903 11336-11336/com.landptf.blog E/ActivityA: onResume()
首先失去焦點然后回調onNewIntent方法，并沒有重建
- singleTask
設置ActivityA的launchMode為singleTask執行如下操作
ActivityA -> ActivityB -> ActivityA
ActivityA啟動
01-19 10:04:49.923 16914-16914/com.landptf.blog E/ActivityA: onCreate()
01-19 10:04:49.927 16914-16914/com.landptf.blog E/ActivityA: onStart()
01-19 10:04:49.927 16914-16914/com.landptf.blog E/ActivityA: onResume()
ActivityB啟動，此時ActivityA處于棧底，ActivityB處于棧頂
01-19 10:05:12.023 16914-16914/com.landptf.blog E/ActivityA: onPause()
01-19 10:05:12.027 16914-16914/com.landptf.blog E/ActivityB: onCreate()
01-19 10:05:12.031 16914-16914/com.landptf.blog E/ActivityB: onStart()
01-19 10:05:12.031 16914-16914/com.landptf.blog E/ActivityB: onResume()
01-19 10:05:12.415 16914-16914/com.landptf.blog E/ActivityA: onSaveInstanceState()
01-19 10:05:12.415 16914-16914/com.landptf.blog E/ActivityA: onStop()
再啟動ActivityA
01-19 10:05:49.103 16914-16914/com.landptf.blog E/ActivityB: onPause()
01-19 10:05:49.107 16914-16914/com.landptf.blog E/ActivityA: onNewIntent()
01-19 10:05:49.107 16914-16914/com.landptf.blog E/ActivityA: onRestart()
01-19 10:05:49.107 16914-16914/com.landptf.blog E/ActivityA: onStart()
01-19 10:05:49.107 16914-16914/com.landptf.blog E/ActivityA: onResume()
01-19 10:05:49.467 16914-16914/com.landptf.blog E/ActivityB: onStop()
01-19 10:05:49.467 16914-16914/com.landptf.blog E/ActivityB: onDestroy()
前面兩步都是正常的執行流程，重點看最后一步，從log中發現ActivityB執行了onDestory方法，因此可以斷定ActivityB已經銷毀，而ActivityA重建但是并沒有執行onCreate方法替代的是onNewIntent方法
- singleInstance
設置ActivityA的launchMode為singleInstance執行如下操作
ActivityA -> ActivityB -> ActivityA
前兩步同上，我們直接看第三步的執行流程，此時ActivityA處于棧底，ActivityB處于棧頂
01-19 10:11:52.963 24180-24180/com.landptf.blog E/ActivityB: onPause()
01-19 10:11:52.963 24180-24180/com.landptf.blog E/ActivityA: onNewIntent()
01-19 10:11:52.963 24180-24180/com.landptf.blog E/ActivityA: onRestart()
01-19 10:11:52.963 24180-24180/com.landptf.blog E/ActivityA: onStart()
01-19 10:11:52.963 24180-24180/com.landptf.blog E/ActivityA: onResume()
01-19 10:11:53.735 24180-24180/com.landptf.blog E/ActivityB: onSaveInstanceState()
01-19 10:11:53.735 24180-24180/com.landptf.blog E/ActivityB: onStop()
可以看出區別在于ActivityB并沒有執行onDestroy方法，也就是說ActivityB并沒有銷毀
此時按Back鍵返回，ActivityB回到了前臺
01-19 10:15:45.947 28069-28069/com.landptf.blog E/ActivityA: onPause()
01-19 10:15:45.951 28069-28069/com.landptf.blog E/ActivityB: onRestart()
01-19 10:15:45.951 28069-28069/com.landptf.blog E/ActivityB: onStart()
01-19 10:15:45.951 28069-28069/com.landptf.blog E/ActivityB: onResume()
01-19 10:15:46.747 28069-28069/com.landptf.blog E/ActivityA: onStop()
01-19 10:15:46.747 28069-28069/com.landptf.blog E/ActivityA: onDestroy()
此時ActivityA已銷毀，再次按Back鍵則返回到主界面
3. 正常流程的生命周期
正常流程上的生命周期，也就是設置launchMode為standard（默認啟動模式，可以省略）
首先啟動ActivityA
01-19 10:20:36.159 318-318/com.landptf.blog E/ActivityA: onCreate()
01-19 10:20:36.163 318-318/com.landptf.blog E/ActivityA: onStart()
01-19 10:20:36.163 318-318/com.landptf.blog E/ActivityA: onResume()
再啟動ActivityB
01-19 10:21:15.323 318-318/com.landptf.blog E/ActivityA: onPause()
01-19 10:21:15.323 318-318/com.landptf.blog E/ActivityB: onCreate()
01-19 10:21:15.327 318-318/com.landptf.blog E/ActivityB: onStart()
01-19 10:21:15.327 318-318/com.landptf.blog E/ActivityB: onResume()
01-19 10:21:15.727 318-318/com.landptf.blog E/ActivityA: onSaveInstanceState()
01-19 10:21:15.727 318-318/com.landptf.blog E/ActivityA: onStop()
這里面注意一點ActivityA的onPause方法在ActivityB的onCreate方法之前執行，因此不要在onPause方法里做耗時操作，否則會影響新Activity的啟動時間
按Back鍵返回到ActivityA
01-19 10:23:32.755 318-318/com.landptf.blog E/ActivityB: onPause()
01-19 10:23:32.755 318-318/com.landptf.blog E/ActivityA: onRestart()
01-19 10:23:32.755 318-318/com.landptf.blog E/ActivityA: onStart()
01-19 10:23:32.755 318-318/com.landptf.blog E/ActivityA: onResume()
01-19 10:23:33.203 318-318/com.landptf.blog E/ActivityB: onStop()
01-19 10:23:33.203 318-318/com.landptf.blog E/ActivityB: onDestroy()
同樣是ActivityB的onPause方法先執行
以上便是我能想到的有關Activity生命周期相關的內容，有錯誤或者不足的地方歡迎大家指出
調試代碼已上傳github，歡迎訪問
