Android Activity啟動(dòng)模式全面解析

更新時(shí)間：2016年02月22日 09:56:39 投稿：mrr

這篇文章主要介紹了Android Activity啟動(dòng)模式全面解析的相關(guān)資料,需要的朋友可以參考下

在android里，有4種activity的啟動(dòng)模式，分別為：

“standard” (默認(rèn))

“singleTop”

“singleTask”

“singleInstance”

在Android應(yīng)用中, Activity是最核心的組件, 如何生成一個(gè)Activity實(shí)例, 可以選擇不同的啟動(dòng)模式, 即LaunchMode. 啟動(dòng)模式主要包括: standard, singleTop, singleTask, singleInstance.

標(biāo)準(zhǔn)模式在每次啟動(dòng)時(shí), 都會(huì)創(chuàng)建實(shí)例; 三種單例模式, 會(huì)根據(jù)情況選擇創(chuàng)建還是復(fù)用實(shí)例. 在Activity啟動(dòng)中, 創(chuàng)建實(shí)例的生命周期: onCreate -> onStart -> onResume; 重用實(shí)例的生命周期: onNewIntent -> onResume.

在AndroidManifest的Activity中, 使用launchMode屬性, 可以設(shè)置啟動(dòng)模式, 默認(rèn)是standard模式; 使用taskAffinity屬性, 并添加包名, 可以設(shè)置Activity棧, 默認(rèn)是當(dāng)前包名, 只能應(yīng)用于single模式.

希望通過本文, 可以更好的理解Activity的啟動(dòng)模式(LaunchMode).

全面解析Activity啟動(dòng)模式(LaunchMode)

觀察Activity棧的腳本, 參考第5點(diǎn) .

adb shell dumpsys activity | sed -n -e '/Stack #/p' -e '/Running activities/,/Run #0/p'

1. Standard

標(biāo)準(zhǔn)模式, 啟動(dòng)Activity的默認(rèn)模式, 被啟動(dòng)的Activity 會(huì)運(yùn)行于啟動(dòng)的Activity 棧, 因此必須使用Activity的Context啟動(dòng), 不能使用Application, 否則會(huì)報(bào)錯(cuò).

如MainActivity啟動(dòng)TestAActivity.

Stack #1:

Running activities (most recent first):
TaskRecord{3caa65e3 #2711 A=me.chunyu.spike.wcl_activity_launchmode_demo U=0 sz=2}
Run #1: ActivityRecord{36b06e99 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestAActivity t2711}
Run #0: ActivityRecord{27396226 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2711}
Stack #0:
Running activities (most recent first):
TaskRecord{27d796c9 #2695 A=com.miui.home U=0 sz=1}
Run #0: ActivityRecord{2e5712cb u0 com.miui.home/.launcher.Launcher t2695}

棧內(nèi)由下到上: MainActivity -> TestAActivity.

2. SingleTop

棧頂復(fù)用模式. 只有Activity位于棧頂, 重復(fù)啟動(dòng)時(shí), 會(huì)使用默認(rèn)實(shí)例, 即單例模式; 如果位于棧內(nèi), 則仍然會(huì)創(chuàng)建實(shí)例.

MainActivity啟動(dòng)TestA, TestA啟動(dòng)TestB, TestB啟動(dòng)自身, TestB是單例. 觀察棧內(nèi)情況, TestB只有一份實(shí)例, 第二次創(chuàng)建復(fù)用.

Stack #1:

Running activities (most recent first):
TaskRecord{12abf566 #2712 A=me.chunyu.spike.wcl_activity_launchmode_demo U=0 sz=3}
Run #2: ActivityRecord{187d7ff7 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestBActivity t2712}
Run #1: ActivityRecord{a551034 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestAActivity t2712}
Run #0: ActivityRecord{22f9cce4 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2712}

棧內(nèi): MainActivity -> TestAActivity -> TestBActivity

MainActivity啟動(dòng)TestA, TestA啟動(dòng)TestB, TestB啟動(dòng)TestC, TestC啟動(dòng)TestB, TestB是單例. 觀察棧內(nèi)情況, 由于TestC是棧頂, TestC啟動(dòng)TestB, TestB不是棧頂, 重新創(chuàng)建TestB實(shí)例, 則保留兩份TestB.

Stack #1:

Running activities (most recent first):
TaskRecord{1792f5f0 #2715 A=me.chunyu.spike.wcl_activity_launchmode_demo U=0 sz=5}
Run #4: ActivityRecord{1e70110b u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestBActivity t2715}
Run #3: ActivityRecord{c7f4dce u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestCActivity t2715}
Run #2: ActivityRecord{254536cd u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestBActivity t2715}
Run #1: ActivityRecord{36b2da15 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestAActivity t2715}
Run #0: ActivityRecord{3a1c4a6a u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2715}

棧內(nèi): MainActivity -> TestAActivity -> TestBActivity ->TestCActivity -> TestBActivity

3. SingleTask

棧內(nèi)復(fù)用模式, 只要Activity在一個(gè)棧中存在, 多次調(diào)用時(shí), 都不會(huì)創(chuàng)建實(shí)例, 即單例模式.

情況包含以下幾種:

(1) 任務(wù)棧不存在, 初次啟動(dòng)SingleTask實(shí)例, 會(huì)創(chuàng)建任務(wù)棧和實(shí)例.

MainActivity啟動(dòng)TestA, TestA啟動(dòng)TestB, TestB是SingleTask, 并且任務(wù)棧不同. 觀察可知, 系統(tǒng)包含兩個(gè)任務(wù)棧, TestB位于其他任務(wù)棧中.

Stack #1:

Running activities (most recent first):
TaskRecord{d5d53d4 #2727 A=me.chunyu.spike.stack U=0 sz=1}
Run #2: ActivityRecord{1d720e55 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestBActivity t2727}
TaskRecord{a3f797d #2726 A=me.chunyu.spike.wcl_activity_launchmode_demo U=0 sz=2}
Run #1: ActivityRecord{ffd689d u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestAActivity t2726}
Run #0: ActivityRecord{192310ac u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2726}

使用taskAffinity屬性, 添加新的Activity棧, 與SingleTask配合使用, Standard模式無效.

新任務(wù)棧是 me.chunyu.spike.stack .

(2) 任務(wù)棧存在, 初次啟動(dòng)SingleTask實(shí)例, 會(huì)直接入棧, 與Standard模式相同.

(3) 任務(wù)棧相同, 再次啟動(dòng)SingleTask實(shí)例, 實(shí)例會(huì)置于棧頂, 并清除其上面實(shí)例, 具有clearTop的效果.

MainActivity啟動(dòng)TestA, TestA啟動(dòng)TestB, TestB是SingleTask, TestB啟動(dòng)TestC, TestC重新啟動(dòng)TestB, 則TestC會(huì)出棧. 觀察可知, TestC出棧, TestB位于棧頂.

Stack #1:

Running activities (most recent first):
TaskRecord{18230815 #2737 A=me.chunyu.spike.wcl_activity_launchmode_demo U=0 sz=3}
Run #4: ActivityRecord{1126c300 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestBActivity t2737}
Run #3: ActivityRecord{3114fee8 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestAActivity t2737}
Run #2: ActivityRecord{f8e235d u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2737}

TestC啟動(dòng)TestB, SingleTask模式, 導(dǎo)致clearTop, TestC出棧.

(4) 任務(wù)棧不同, 再次啟動(dòng)SingleTask實(shí)例, 會(huì)導(dǎo)致任務(wù)棧切換, 后臺(tái)置于前臺(tái).

這比較難理解.MainActivity啟動(dòng)TestA, TestA啟動(dòng)TestB(SingleTask實(shí)例, 不同任務(wù)棧), TestB啟動(dòng)TestC(與B類似), 則MainActivity和TestA相同棧, TestB和TestC相同棧, 此時(shí)棧頂是TestC. 按Home鍵, 再次啟動(dòng)應(yīng)用, 則默認(rèn)任務(wù)棧會(huì)啟動(dòng), TestA啟動(dòng), TestA啟動(dòng)TestC. 應(yīng)用當(dāng)前狀態(tài)如下.

Stack #1:

Running activities (most recent first):
TaskRecord{1d05e6c9 #2754 A=me.chunyu.spike.stack U=0 sz=2}
Run #4: ActivityRecord{3f77e822 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestCActivity t2754}
TaskRecord{3fe736d0 #2753 A=me.chunyu.spike.wcl_activity_launchmode_demo U=0 sz=2}
Run #3: ActivityRecord{15f0470e u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestAActivity t2753}
TaskRecord{1d05e6c9 #2754 A=me.chunyu.spike.stack U=0 sz=2}
Run #2: ActivityRecord{181229e6 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestBActivity t2754}
TaskRecord{3fe736d0 #2753 A=me.chunyu.spike.wcl_activity_launchmode_demo U=0 sz=2}
Run #1: ActivityRecord{28628d61 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2753}
TaskRecord{2d646058 #2719 A=com.android.incallui U=0 sz=1}

TestC至于棧頂, 點(diǎn)擊Back鍵, 不是返回TestA(啟動(dòng)TestC的實(shí)例), 而是TestB, 即優(yōu)先返回相同棧的實(shí)例. 再次是TestA, 然后是MainActivity, 依次出棧.

4. SingleInstance

單實(shí)例模式, 啟動(dòng)時(shí), 系統(tǒng)會(huì)為其創(chuàng)造一個(gè)單獨(dú)的任務(wù)棧, 以后每次使用, 都會(huì)使用這個(gè)單例, 直到其被銷毀, 屬于真正的單例模式.

示例: MainActivity啟動(dòng)TestA, TestA啟動(dòng)TestB(SingleInstance模式),

TestB啟動(dòng)TestC, TestC再啟動(dòng)TestB, 則仍啟動(dòng)上一次的TestB,

TestC合并入默認(rèn)棧(MainActivity+TestA).

Stack #1:

Running activities (most recent first):
TaskRecord{384e3928 #2765 A=me.chunyu.spike.wcl_activity_launchmode_demo U=0 sz=1}
Run #3: ActivityRecord{1ffc5b6b u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestBActivity t2765}
TaskRecord{2ad03544 #2764 A=me.chunyu.spike.wcl_activity_launchmode_demo U=0 sz=3}
Run #2: ActivityRecord{293d8c37 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestCActivity t2764}
Run #1: ActivityRecord{158bc0f3 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestAActivity t2764}
Run #0: ActivityRecord{77691cf u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2764}

5. startActivityForResult

Thx@回調(diào)的幸福時(shí)光

startActivityForResult不同于startActivity, 使用LaunchMode模式啟動(dòng)Activity時(shí), 也會(huì)有一些不同, 可以正常傳遞數(shù)據(jù), 但是無法連續(xù)創(chuàng)建自己時(shí), 會(huì)生成多份實(shí)例.

TestB(singleTask模式)使用startActivity創(chuàng)建自己時(shí), 會(huì)使用默認(rèn)實(shí)例, 即單例; 而使用startActivityForResult創(chuàng)建自己時(shí), 會(huì)生成一份新的示例.

Stack #1:

Running activities (most recent first):
TaskRecord{323200ac #2786 A=me.chunyu.clwang.stack U=0 sz=3}
Run #4: ActivityRecord{3f9e14f3 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestBActivity t2786}
Run #3: ActivityRecord{30d8f17b u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestBActivity t2786}
Run #2: ActivityRecord{11b95b5c u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestBActivity t2786}
TaskRecord{c86e175 #2785 A=me.chunyu.spike.wcl_activity_launchmode_demo U=0 sz=2}
Run #1: ActivityRecord{3558d7c4 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.TestAActivity t2785}
Run #0: ActivityRecord{1b8620c u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2785}

由此可知, 因?yàn)閟tartActivityForResult需要返回值, 會(huì)保留實(shí)例, 覆蓋單例效果.

注意: 4.x版本通過startActivityForResult啟動(dòng)singleTask, 無法正常獲取返回值, 參考 .

5.x以上版本修復(fù)此問題, 考慮兼容性, 不推薦使用startActivityForResult和singleTask.

啟動(dòng)模式做為Activity的重要屬性, 還是需要比較透徹的掌握.

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