概述：
先祭出神圖：
從上面的圖中可以看到一些東西
- onResume：Activity快要顯示了盗痒，但是官方說用這種方式判斷是否顯示不準(zhǔn)確周伦，應(yīng)該使用
onWindowFocusChanged來監(jiān)聽磕蛇。 - onPause：是失去焦點(diǎn)不可與用戶交互
- onStop：是Activity不可見的分界線，比如被一個(gè)透明的activity覆蓋就不會(huì)調(diào)用原activity的onStop方法
然后從幾個(gè)場(chǎng)景分析
創(chuàng)建一個(gè)Activity达罗，這個(gè)創(chuàng)建的Activity的生命周期：
07-19 17:01:04.555 11692-11692/com.ironman.activitylifecycle D/activity-life-cycle: onCreate
07-19 17:01:04.666 11692-11692/com.ironman.activitylifecycle D/activity-life-cycle: onStart
07-19 17:01:04.667 11692-11692/com.ironman.activitylifecycle D/activity-life-cycle: onResume
從一個(gè)activity打開另一個(gè)activity
07-19 17:38:45.576 12000-12000/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onPause
07-19 17:38:45.617 12000-12000/com.ironman.activitylifecycle D/activity-life-cycle: ScrollingActivity-onCreate
07-19 17:38:45.757 12000-12000/com.ironman.activitylifecycle D/activity-life-cycle: ScrollingActivity-onStart
07-19 17:38:45.758 12000-12000/com.ironman.activitylifecycle D/activity-life-cycle: ScrollingActivity-onResume
07-19 17:38:46.395 12000-12000/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onStop
會(huì)先運(yùn)行當(dāng)前activity的onPause低斋，讓他失去焦點(diǎn)不能與用戶交互，然后調(diào)用創(chuàng)建以及顯示第二個(gè)activity的方法愉择，然后調(diào)用第一個(gè)activity的onStop方法讓第一個(gè)Activity不顯示劫乱。
官方文檔里有一段對(duì)onPause方法的描述：
Called as part of the activity lifecycle when an activity is going into the background, but has not (yet) been killed. The counterpart to onResume().When activity B is launched in front of activity A, this callback will be invoked on A. B will not be created until A's onPause() returns, so be sure to not do anything lengthy here.
也就是不要在onPause里做太多耗時(shí)的工作，如果啟動(dòng)另一個(gè)activity锥涕，他會(huì)等著當(dāng)前activity的onPause執(zhí)行完才會(huì)去創(chuàng)建另一個(gè)Activity衷戈。
從一個(gè)activity打開一個(gè)透明的activity
07-19 18:55:09.797 10352-10352/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onPause
07-19 18:55:09.824 10352-10352/com.ironman.activitylifecycle D/activity-life-cycle: TransparentActivity-onCreate
07-19 18:55:09.829 10352-10352/com.ironman.activitylifecycle D/activity-life-cycle: TransparentActivity-onStart
07-19 18:55:09.830 10352-10352/com.ironman.activitylifecycle D/activity-life-cycle: TransparentActivity-onResume
可以看到前一個(gè)activity的onStop是沒有被調(diào)用的。
從一個(gè)activity打開一個(gè)dialog
打開一個(gè)dialog并不會(huì)觸發(fā)activity生命周期层坠，dialog是這個(gè)activity內(nèi)部的view并不會(huì)導(dǎo)致這個(gè)activity顯示或者隱藏殖妇。
點(diǎn)擊home鍵
07-19 18:24:53.644 18605-18605/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onPause
07-19 18:24:54.023 18605-18605/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onStop
從home鍵返回：
07-19 19:28:55.453 18586-18586/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onRestart
07-19 19:28:55.464 18586-18586/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onStart
07-19 19:28:55.464 18586-18586/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onResume
按返回鍵
1. 從第二個(gè)頁(yè)面返回到第一個(gè)頁(yè)面：
07-19 18:12:31.523 18605-18605/com.ironman.activitylifecycle D/activity-life-cycle: ScrollingActivity-onPause
07-19 18:12:31.535 18605-18605/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onRestart
07-19 18:12:31.535 18605-18605/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onStart
07-19 18:12:31.536 18605-18605/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onResume
07-19 18:12:32.022 18605-18605/com.ironman.activitylifecycle D/activity-life-cycle: ScrollingActivity-onStop
07-19 18:12:32.022 18605-18605/com.ironman.activitylifecycle D/activity-life-cycle: ScrollingActivity-onDestroy
可以看到先調(diào)用的是當(dāng)前acitivity的onPause，然后在恢復(fù)前一個(gè)activity破花，前一個(gè)activity是從onRestart來的谦趣，所以只是stop了并沒有銷毀疲吸，當(dāng)前一個(gè)activity的onResum運(yùn)行完畢了之后返回的那個(gè)activity就被銷毀了。
2.如果是從透明的activity返回：
07-19 19:00:02.664 10352-10352/com.ironman.activitylifecycle D/activity-life-cycle: TransparentActivity-onPause
07-19 19:00:02.687 10352-10352/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onResume
07-19 19:00:02.717 10352-10352/com.ironman.activitylifecycle D/activity-life-cycle: TransparentActivity-onStop
07-19 19:00:02.717 10352-10352/com.ironman.activitylifecycle D/activity-life-cycle: TransparentActivity-onDestroy
相對(duì)于非透明的activity蔚润，少運(yùn)行了onRestart和onStart兩個(gè)方法
按返回鍵退出app：
07-19 18:18:50.679 18605-18605/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onPause
07-19 18:18:51.067 18605-18605/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onStop
07-19 18:18:51.073 18605-18605/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onDestroy
其實(shí)就是單頁(yè)面的銷毀的生命周期磅氨，依次onPause, onStop, onDestroy
關(guān)閉屏幕（也就是點(diǎn)擊電源鍵）
07-19 19:01:45.613 10352-10352/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onPause
07-19 19:01:45.676 10352-10352/com.ironman.activitylifecycle D/activity-life-cycle: MainActivity-onStop
總結(jié)一下
- 創(chuàng)建一個(gè)activity會(huì)依次執(zhí)行onCreate, onStart, onResume
- 從一個(gè)activity啟動(dòng)另一個(gè)activity會(huì)先調(diào)用當(dāng)前activity的onResume，然后在創(chuàng)建并顯示要啟動(dòng)的activity嫡纠。
- 從非透明activity返回的時(shí)候會(huì)先調(diào)用當(dāng)前的onPause烦租，然后調(diào)用前一個(gè)activitiy的onRestart、onStart除盏、onResme叉橱，然后在調(diào)用這個(gè)Activity的onStop，onDestroy者蠕。
- 從透明的activity返回的時(shí)候會(huì)先調(diào)用當(dāng)前activity的onPause窃祝，然后調(diào)用前一個(gè)activity的onResume，然后調(diào)用這個(gè)透明activity的onStop踱侣，onDestroy粪小。
- 透明的Activity比較特殊，他會(huì)讓別的activity的一些生命周期不被調(diào)用比如onStop等待抡句。
- onResume方法里不能有太耗時(shí)的操作探膊，因?yàn)楫?dāng)啟動(dòng)另一個(gè)activity的時(shí)候，當(dāng)前的onResume沒有返回不會(huì)去創(chuàng)建要啟動(dòng)的那個(gè)activity待榔。
