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android6.0源码分析之Activity启动过程

發(fā)布時(shí)間：2025/3/15 编程问答 35 豆豆

生活随笔收集整理的這篇文章主要介紹了 android6.0源码分析之Activity启动过程小編覺(jué)得挺不錯(cuò)的,現(xiàn)在分享給大家,幫大家做個(gè)參考.

Activity最為Android開(kāi)發(fā)者最熟悉的組件，由ActivityManagerService服務(wù)進(jìn)行調(diào)度管理，而ActivityManagerService的啟動(dòng)過(guò)程在activitymanagerservice服務(wù)源碼分析一文中進(jìn)行了詳細(xì)分析，本文基于其對(duì)Activity的啟動(dòng)過(guò)程進(jìn)行分析，同時(shí)也將分析AMS對(duì)Activity的調(diào)度管理。

1、 Activity的啟動(dòng)模式

啟動(dòng)模式實(shí)際上就是為了控制Activity與Task之間的關(guān)系，目前共有一下四種模式：standard、singleTop、singleTask以及singleInstance，默認(rèn)的模式為standard模式。?
注意：建議一般的開(kāi)發(fā)者不要輕易使用后兩種模式，因?yàn)椴煌哪Ｊ?#xff0c;其出棧的順序不同，可能會(huì)導(dǎo)致用戶(hù)按下返回鍵時(shí)，會(huì)有不一樣的用戶(hù)體驗(yàn)，對(duì)于啟動(dòng)模式的分析，推薦仔細(xì)閱讀深入講解Android中Activity launchMode,這篇文章使用圖文并用的方式，很好的分析了Activity各種模式的區(qū)別，本文不再分析啟動(dòng)模式。

2、Activity的啟動(dòng)時(shí)機(jī)

Activity作為android非常重要的組件，那么我們會(huì)在哪些時(shí)機(jī)啟動(dòng)它呢？?
通常有如下幾種情形：?
1.?android AM命令?
android系統(tǒng)為開(kāi)發(fā)者提供了adb工具，而在adb的基礎(chǔ)上執(zhí)行adb shell就可以從PC上對(duì)手機(jī)側(cè)執(zhí)行shell命令。如啟動(dòng)瀏覽器：am start -n com.android.browser/com.android.browser.BrowserActivity。?
2.?啟動(dòng)AMS服務(wù)時(shí)?
在啟動(dòng)AMS服務(wù)時(shí)，在最后調(diào)用AMS的systemReady的最后階段會(huì)啟動(dòng)Home界面，此時(shí)就會(huì)啟動(dòng)一個(gè)Activity。?
3.?調(diào)用startActivity()和startActivityForResult()方法時(shí)?
這是我們最常用也最熟悉的啟動(dòng)Activity的方式。

3、AM命令行啟動(dòng)Activity的過(guò)程分析

在adb中可以使用AM命令，同時(shí)在應(yīng)用程序中，也可以通過(guò)AM命令來(lái)啟動(dòng)指定的Activity，AM是一個(gè)腳本命令，它還可以啟動(dòng)Service，發(fā)送廣播等。

3.1 Am 框架層調(diào)用流程分析

adb執(zhí)行Am命令后，最終會(huì)執(zhí)行Am.java的main方法，其代碼如下：

它調(diào)用的是抽象父類(lèi)BaseCommand類(lèi)的run方法:

跟其他命令腳本類(lèi)似，如果參數(shù)為空，顯示使用說(shuō)明，否則調(diào)用onRun()方法，它是一個(gè)抽象方法，在Am.java中有實(shí)現(xiàn):

命令參數(shù)不同，其執(zhí)行的操作不同，就本節(jié)來(lái)說(shuō)，其參數(shù)為start，所以將會(huì)執(zhí)行runStart()方法來(lái)啟動(dòng)Activity:

startActivityAsUser()最后也是調(diào)用AMS的startActivityAndWait()方法，所以Am命令框架層的調(diào)用結(jié)束，其調(diào)用時(shí)序如下：?

3.2 AMS啟動(dòng)Activity流程分析

Am命令將啟動(dòng)Activity的工作交給了AMS來(lái)進(jìn)行，首先看startActivityAndWait()方法，它直接調(diào)用StackSupervisor類(lèi)的startActivityMayWait()方法，其代碼如下：

首先通過(guò)PKMS查找匹配的ActivityInfo，然后獲取調(diào)用者的pid,uid等信息，由于本文的caller為空，得到的是Am所在進(jìn)程的pid和uid。接著調(diào)用startActivityLocked()方法啟動(dòng)Activity，最后再調(diào)用mService.wait()方法來(lái)等待啟動(dòng)結(jié)果，并對(duì)返回值進(jìn)行一些處理，此處的等待主要是Am參數(shù)中有一個(gè)-W選項(xiàng)，若無(wú)此選項(xiàng)，則不會(huì)有這個(gè)等待，最后再將啟動(dòng)結(jié)果res返回。?
繼續(xù)分析startActivityLocked()方法:

<code class="hljs r has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">//ActivityStackSupervisor.java final int startActivityLocked(...){int err = ActivityManager.START_SUCCESS;ProcessRecord callerApp = null;if (caller != null) {//如果caller不為空，從AMS中找到它所屬的ProcessRecord即進(jìn)程，本文此處為nullcallerApp = mService.getRecordForAppLocked(caller);if (callerApp != null) {callingPid = callerApp.pid;callingUid = callerApp.info.uid;} else {err = ActivityManager.START_PERMISSION_DENIED;}}...//sourceRecord用于描述啟動(dòng)目標(biāo)Activity的那個(gè)ActivityActivityRecord sourceRecord = null;//resultRecord用于描述接收啟動(dòng)結(jié)果的Activity，即onActivityResult將被調(diào)用以通知啟動(dòng)結(jié)果ActivityRecord resultRecord = null;...//獲取Intent設(shè)置的啟動(dòng)標(biāo)志final int launchFlags = intent.getFlags();//此部分與LaunchMode類(lèi)似，它用于控制Activity啟動(dòng)結(jié)果的通知if ((launchFlags & Intent.FLAG_ACTIVITY_FORWARD_RESULT) != 0 && sourceRecord != null) {...}...//檢查權(quán)限final int startAnyPerm = mService.checkPermission(START_ANY_ACTIVITY, callingPid, callingUid);...//可為AMS設(shè)置IActivityController類(lèi)型的監(jiān)聽(tīng)者，AMS有任何動(dòng)靜都將回調(diào)該監(jiān)聽(tīng)者if (mService.mController != null) {try {Intent watchIntent = intent.cloneFilter();//交給回調(diào)對(duì)象處理，由它判斷能否繼續(xù)后面的行程abort |= !mService.mController.activityStarting(watchIntent,aInfo.applicationInfo.packageName);} catch (RemoteException e) {mService.mController = null;}}if (abort) {//通知resultRecordif (resultRecord != null) {resultStack.sendActivityResultLocked(-1, resultRecord, resultWho, requestCode,Activity.RESULT_CANCELED, null);} ActivityOptions.abort(options);return ActivityManager.START_SUCCESS;}//創(chuàng)建一個(gè)ActivityRecord對(duì)象ActivityRecord r = new ActivityRecord(mService,this,callerApp,callingUid,...);...final ActivityStack stack = mFocusedStack;if (voiceSession == null && (stack.mResumedActivity == null|| stack.mResumedActivity.info.applicationInfo.uid != callingUid)) {//判斷是否有權(quán)限切換Applicationif (!mService.checkAppSwitchAllowedLocked(callingPid, callingUid,realCallingPid, realCallingUid, "Activity start")) {PendingActivityLaunch pal =new PendingActivityLaunch(r, sourceRecord,startFlags,stack);//將Pending的請(qǐng)求保存到AMS的mPendingActivityLaunches變量中mPendingActivityLaunches.add(pal);ActivityOptions.abort(options);return ActivityManager.START_SWITCHES_CANCELED;}}if (mService.mDidAppSwitch) {mService.mAppSwitchesAllowedTime = 0;} else {mService.mDidAppSwitch = true;}//啟動(dòng)處于Pending狀態(tài)的ActivitydoPendingActivityLaunchesLocked(false);//調(diào)用此函數(shù)繼續(xù)啟動(dòng)Activityerr = startActivityUncheckedLocked(r, sourceRecord, voiceSession, voiceInteractor,startFlags, true, options, inTask);//做一些結(jié)果處理...return err; } </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; 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padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; 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padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; 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padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li></ul>

此段代碼的主要工作就是處理sourceRecord和resultRecord，然后再處理app switch屬性，如果當(dāng)前禁止app switch，則將本次啟動(dòng)保存起來(lái)，等允許app switch時(shí)再處理，最后再調(diào)用startActivityUncheckedLocked()方法處理本次Activity啟動(dòng)請(qǐng)求：

首先根據(jù)Activity的啟動(dòng)模式以及傳入的參數(shù)來(lái)確定是否需要?jiǎng)?chuàng)建新的Task以及l(fā)aunchFlags，然后調(diào)用startActivityLocked()方法繼續(xù)啟動(dòng)(這里的方法參數(shù)與前面同名方法的不一樣，屬于重載函數(shù))，繼續(xù)分析啟動(dòng)過(guò)程：

此方法將根據(jù)傳入的參數(shù)來(lái)找到此Activity所在的任務(wù)，以及進(jìn)行相應(yīng)判斷將其加入到相應(yīng)的history stack的最頂端(棧頂)，最后再調(diào)用ActivityStack的resumeTopActivitiesLocked方法來(lái)啟動(dòng)棧頂?shù)腁ctivity，繼續(xù)分析resumeTopActivitiesLocked方法:

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">//ActivityStack.java boolean resumeTopActivitiesLocked(ActivityStack targetStack, ActivityRecord target,Bundle targetOptions){if (targetStack == null) {//如果目的任務(wù)為NULL,則啟動(dòng)當(dāng)前聚焦的任務(wù)targetStack = mFocusedStack;}//啟動(dòng)targetStackboolean result = false;if (isFrontStack(targetStack)) {result = targetStack.resumeTopActivityLocked(target, targetOptions);}for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {final ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {final ActivityStack stack = stacks.get(stackNdx);if (stack == targetStack) {//上面已經(jīng)啟動(dòng)了continue;}if (isFrontStack(stack)) {stack.resumeTopActivityLocked(null);}}}return result; } </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li></ul>

此方法很簡(jiǎn)單就是根據(jù)當(dāng)前任務(wù)，調(diào)用相應(yīng)的resumeTopActivityLocked()方法來(lái)啟動(dòng)，而resumeTopActivityLocked也只是簡(jiǎn)單的調(diào)用了resumeTopActivityInnerLocked方法，所以分析resumeTopActivityInnerLocked方法：

<code class="hljs r has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">//ActivityStack.java private boolean resumeTopActivityInnerLocked(ActivityRecord prev, Bundle options){//找到第一個(gè)還沒(méi)有結(jié)束的Activityfinal ActivityRecord next = topRunningActivityLocked(null);...//確保擁有此Activity的任務(wù)已經(jīng)啟動(dòng)if (mService.mStartedUsers.get(next.userId) == null) {return false;}...//設(shè)置啟動(dòng)的UidmStackSupervisor.setLaunchSource(next.info.applicationInfo.uid);...ActivityStack lastStack = mStackSupervisor.getLastStack();if (next.app != null && next.app.thread != null) {//進(jìn)程，線(xiàn)程都存在//將此Activity置為VisiblemWindowManager.setAppVisibility(next.appToken, true);// schedule launch ticks to collect information about slow apps.next.startLaunchTickingLocked();ActivityRecord lastResumedActivity =lastStack == null ? null :lastStack.mResumedActivity;ActivityState lastState = next.state;next.state = ActivityState.RESUMED;mResumedActivity = next;next.task.touchActiveTime();mRecentTasks.addLocked(next.task);mService.updateLruProcessLocked(next.app, true, null);updateLRUListLocked(next);mService.updateOomAdjLocked();...try {// Deliver all pending results.ArrayList<ResultInfo> a = next.results;if (a != null) {final int N = a.size();if (!next.finishing && N > 0) {next.app.thread.scheduleSendResult(next.appToken, a);}}if (next.newIntents != null) {next.app.thread.scheduleNewIntent(next.newIntents, next.appToken);}...next.sleeping = false;mService.showAskCompatModeDialogLocked(next);next.app.pendingUiClean = true;next.app.forceProcessStateUpTo(mService.mTopProcessState);next.clearOptionsLocked();//因?yàn)檫M(jìn)程，線(xiàn)程都存在，所以只需恢復(fù)此Activitynext.app.thread.scheduleResumeActivity(next.appToken, next.app.repProcState,mService.isNextTransitionForward(), resumeAnimOptions);} catch (Exception e) {// 如果發(fā)生異常，需要重啟此Activity，注意此方法最后一個(gè)參數(shù)為falsemStackSupervisor.startSpecificActivityLocked(next, true, false);return true;}} else {//因?yàn)檫M(jìn)程或者線(xiàn)程為空，所以需要重新啟動(dòng)activity，此處最后一個(gè)參數(shù)為truemStackSupervisor.startSpecificActivityLocked(next, true, true);}return true; }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li></ul>

如代碼可知：如果當(dāng)前需要啟動(dòng)的Activity所在的進(jìn)程和線(xiàn)程都已經(jīng)創(chuàng)建，則調(diào)用ActivityThread的scheduleResumeActivity方法來(lái)恢復(fù)此Activity，此時(shí)如果發(fā)生異常，則調(diào)用startSpecificActivityLocked來(lái)重新啟動(dòng)此Activity，當(dāng)然，我們注意到，當(dāng)Activity所在的進(jìn)程或者線(xiàn)程為啟動(dòng)時(shí)，它也是調(diào)用startSpecificActivityLocked方法來(lái)重新啟動(dòng)此Activity，但區(qū)別在此方法的最后一個(gè)參數(shù)，即進(jìn)程和線(xiàn)程已經(jīng)啟動(dòng)了的為flase，否則為true，下面分析startSpecificActivityLocked()方法：

由代碼可知，它同樣會(huì)先判斷線(xiàn)程和進(jìn)程是否已啟動(dòng)，如果已啟動(dòng)，調(diào)用realStartActivityLocked來(lái)啟動(dòng)Activity，否則調(diào)用AMS的startProcessLocked來(lái)啟動(dòng)進(jìn)程，由于Am命令和AMS的Hone界面啟動(dòng)都是進(jìn)程未啟動(dòng)的情況，所以此處先分析分兩個(gè)階段分析,此階段的時(shí)序圖如下：?

3.2.1 AMS啟動(dòng)Activity所在進(jìn)程的流程分析

由于android下的Java進(jìn)程都是由Zygote進(jìn)程fork出來(lái)的，所以分析此流程之前，需要對(duì)Zygote的原理有一些了解，對(duì)Zygote進(jìn)程的分析請(qǐng)參考android源碼分析之Zygote進(jìn)程分析，先從AMS的startProcessLocked方法進(jìn)行分析：

由代碼可知，它調(diào)用了Process的start方法來(lái)啟動(dòng)進(jìn)程，繼續(xù)分析start方法：

繼續(xù)看startViaZygote方法：

同樣，它首先進(jìn)行一些參數(shù)處理，如runtime的參數(shù)等等，繼續(xù)分析zygoteSendArgsAndGetResult方法：

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">//Process.java private static ProcessStartResult zygoteSendArgsAndGetResult(ZygoteState zygoteState, ArrayList<String> args) throws ZygoteStartFailedEx{try {//通過(guò)socket通信，此處將進(jìn)程啟動(dòng)的啟動(dòng)寫(xiě)進(jìn)socket的輸出流final BufferedWriter writer = zygoteState.writer;final DataInputStream inputStream = zygoteState.inputStream;writer.write(Integer.toString(args.size()));writer.newLine();int sz = args.size();for (int i = 0; i < sz; i++) {String arg = args.get(i);if (arg.indexOf('\n') >= 0) {throw new ZygoteStartFailedEx("embedded newlines not allowed");}writer.write(arg);writer.newLine();}writer.flush();// Should there be a timeout on this?ProcessStartResult result = new ProcessStartResult();result.pid = inputStream.readInt();if (result.pid < 0) {throw new ZygoteStartFailedEx("fork() failed");}result.usingWrapper = inputStream.readBoolean();return result;} catch (IOException ex) {zygoteState.close();throw new ZygoteStartFailedEx(ex);} }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li></ul>

此方法，將會(huì)與ZygoteInit中runSelectLoop()方法啟動(dòng)的socket進(jìn)程通信，而Zygote進(jìn)程將會(huì)為此Activity創(chuàng)建新的進(jìn)程，而子進(jìn)程創(chuàng)建好后，會(huì)調(diào)用ActivityThread的主線(xiàn)程的main方法，所以繼續(xù)分析ActivityThread的main方法：

此段代碼將會(huì)創(chuàng)建一個(gè)主線(xiàn)程對(duì)象ActivityThread，并將啟動(dòng)Looper以及獲取主線(xiàn)程的Handler來(lái)進(jìn)行消息處理，并調(diào)用attach方法來(lái)進(jìn)行線(xiàn)程處理，繼續(xù)分析attach方法：

它調(diào)用了AMS的attachApplication方法來(lái)對(duì)線(xiàn)程進(jìn)行包裝，繼續(xù)查看attachApplication方法：

只是調(diào)用了attachApplicationLocked方法：

此處回調(diào)了ActivityThread的bindApplication方法，通過(guò)bindApplication方法來(lái)對(duì)應(yīng)用進(jìn)行相應(yīng)的初始化，然后調(diào)用了ActivityStackSupervisor的attachApplicationLocked方法，它最后會(huì)調(diào)用realStartActivityLocked方法來(lái)真正啟動(dòng)Activity，本節(jié)不對(duì)Activity的調(diào)度做分析，所以先分析bindApplication方法。

首先通過(guò)sendMessage發(fā)送BIND_APPLICATION信號(hào)給ApplicationThread，ApplicationThread的handler會(huì)對(duì)此進(jìn)行處理。至此，有關(guān)進(jìn)程和線(xiàn)程的流程分析結(jié)束，其時(shí)序圖如下：?

3.2.2 AMS對(duì)Activity的調(diào)度分析

上一節(jié)分析了進(jìn)程的創(chuàng)建和主線(xiàn)程的初始化過(guò)程，本節(jié)將分析AMS對(duì)Activity生命周期的管理調(diào)度，此處涉及到的主要有如下幾個(gè)類(lèi)：ActivityStackSupervisor，ActivityStack，ActivityThread，ApplicationThread，ApplicationThread.H，Instrumentation等。

系統(tǒng)通過(guò)AMS來(lái)管理應(yīng)用進(jìn)程的生命周期，當(dāng)然包括應(yīng)用的Activity、Service等的生命周期。AMS是一個(gè)獨(dú)立的進(jìn)程，因此它要管理應(yīng)用進(jìn)程，必然要進(jìn)行跨進(jìn)程交互。其交互如下圖：?
?
其中：?
ActivityManagerProxy——AMS的代理，供應(yīng)用進(jìn)程調(diào)用。通過(guò)ActivityManagerNative.getDefault()獲取。?
ApplicationThreadProxy——應(yīng)用進(jìn)程的代理，供AMS進(jìn)程調(diào)用。應(yīng)用啟動(dòng)時(shí)，會(huì)將應(yīng)用進(jìn)程的代理傳遞到AMS跨進(jìn)程通信，一般都會(huì)用到遠(yuǎn)程代理。ActivityManagerService繼承于Binder即它實(shí)現(xiàn)了IBinder接口，所以它可以用于進(jìn)程間通信。在app進(jìn)程啟動(dòng)時(shí)，會(huì)建立一個(gè)Binder線(xiàn)程池，專(zhuān)門(mén)用來(lái)處理Binder IPC事物。?
在3.2.1節(jié)中已經(jīng)分析了：AMS在啟動(dòng)好了進(jìn)程之后，會(huì)調(diào)用realStartActivityLocked方法來(lái)啟動(dòng)Activity，所以先看realStartActivityLocked方法：

由代碼可知：它是通過(guò)調(diào)用ActivityThread.ApplicationThread類(lèi)的scheduleLaunchActivity方法來(lái)啟動(dòng)Activity的：

此方法將發(fā)送一個(gè)LAUNCH_ACTIVITY的Message給ApplicationThread.H的handler進(jìn)行處理，而此handler將會(huì)調(diào)用ApplicationThread的handleLaunchActivity進(jìn)行啟動(dòng)處理：

如代碼：首先調(diào)用performLaunchActivity來(lái)啟動(dòng)Activity，即調(diào)用OnCreate()生命周期，然后會(huì)調(diào)用handleResumeActivity方法來(lái)調(diào)用OnResume()生命周期。首先看performLaunchActivity():

此方法將會(huì)通過(guò)類(lèi)加載器加載組件并新建Activity，然后通過(guò)調(diào)用Instrumentation的callActivityOnCreate方法來(lái)啟動(dòng)Activity，其方法定義如下：

此方法里調(diào)用了performCreate方法：

<code class="hljs scss has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">//Activity.java final void performCreate(Bundle icicle) {onCreate(icicle);mActivityTransitionState.readState(icicle);performCreateCommon(); }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

顯然，它最后會(huì)調(diào)用定義的Activity的OnCreate()方法，即執(zhí)行了OnCreate生命周期，同理其他生命周期的執(zhí)行過(guò)程與此類(lèi)似。OnCreate生命周期的時(shí)序圖如下：?

4、startActivity方法啟動(dòng)Activity的過(guò)程分析

本節(jié)將對(duì)我們熟悉的調(diào)用startActivity的啟動(dòng)方式進(jìn)行分析，同樣基于的源碼版本是android 6.0，這種情況下，應(yīng)用進(jìn)程已經(jīng)存在，不需要進(jìn)行應(yīng)用進(jìn)程的創(chuàng)建啟動(dòng)（區(qū)別于AMS啟動(dòng)Home桌面等啟動(dòng)新應(yīng)用的方式），首先看startActivity()代碼：

由代碼可知，startActivity()最終只是對(duì)startActivityForResult()方法進(jìn)行簡(jiǎn)單調(diào)用，所以只需對(duì)startActivityForResult()繼續(xù)分析：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">public void startActivityForResult(Intent intent,int requestCode,@Nullable Bundle options){if(mParent == null){//執(zhí)行Activity啟動(dòng)，并返回啟動(dòng)結(jié)果Instrumentation.ActivityResult ar = mInstrumentation.execStartActivity(this,mMainThread.getApplicationThread(),mToken,this,intent,requestCode,options);if(ar != null){//向主線(xiàn)程發(fā)送啟動(dòng)結(jié)果mMainThread.sendActivityResult(mToken,mEmbeddedID,requestCode,ar.getResultCode(),ar.getResultData());}if(requestCode > 0){//啟動(dòng)成功mStartedActivity = true;}cancelInputsAndStartExitTransition(options);}else{//如果mParent不為空，此時(shí)最后還是會(huì)調(diào)用Instrumentation的execStartActivity()方法if(options != null){mParent.startActivityFromChild(this,intent,requestCode,options);}else{mParent.startActivityFromChild(this,intent,requestCode);}} }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul>

最后還是會(huì)調(diào)用Instrumentation的execStartActivity()方法來(lái)啟動(dòng)Activity，并將啟動(dòng)的結(jié)果返回給該應(yīng)用的主線(xiàn)程，繼續(xù)分析execStartActivity()方法：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">public ActivityResult execStartActivity(Context who,IBinder contextThread,IBinder token,String target,Intent intent,int requestCode,Bundle options){//獲取通信存根類(lèi)，它派發(fā)消息給ActivityThread主線(xiàn)程，而主線(xiàn)程的mH的handler會(huì)進(jìn)行相應(yīng)處理IApplicationThread whoThread = (IApplicationThread)contextThread;...try{intent.migrateExtraStreanToClipData();intent.prepareToLeaveProcess();//調(diào)用AMS的startActivity()方法，即進(jìn)入AMS的調(diào)度管理int result = ActivityManagerNative.getDefault().startActivity(whoThread,who.getBasePackageName(),intent,intent.resolveTypeIfNeeded(who.getContentResolver()),token,target,requestCode,0,null,options); //檢查啟動(dòng)結(jié)果checkStartActivityResult(result,intent);}catch(RemoteException e){throw new RuntimeException("Failure from system",e);}return null; }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li></ul>

首先獲得IApplicationThread對(duì)象，它用于與主線(xiàn)程進(jìn)行通信，ActivityManagerNative.getDefault()獲取的是AMS對(duì)象，所以此處將啟動(dòng)任務(wù)交給了AMS進(jìn)行調(diào)度管理。startActivity方法會(huì)調(diào)用startActivityAsUser()方法：

至此，它的分析同第3節(jié)中的過(guò)程一致，此處不再做分析，只是本節(jié)的啟動(dòng)不需要啟動(dòng)進(jìn)程，所以它的執(zhí)行分支不一致。

原文地址：　http://blog.csdn.net/yangzhihuiguming/article/details/51722054

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