android 8.0重启软件,11 App启动流程-Android 8.0-2

以你之姓@ 2022-10-05 12:45 214阅读 0赞

1. ActivityThread启动Activity的过程

通过前篇的介绍，我们知道目前的代码逻辑运行在应用程序进程中。先来查看ActivityThread启动Activity的过程的时序图。

我们接着来查看ApplicationThread的scheduleLaunchActivity方法，其中ApplicationThread是ActivityThread的内部类，应用程序进程创建后会运行代表主线程的实例ActivityThread，它管理着当前应用程序进程的线程。ApplicationThread的scheduleLaunchActivity方法如下所示。

frameworks/base/core/java/android/app/ActivityThread.java

@Override

public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,

ActivityInfo info, Configuration curConfig, Configuration overrideConfig,

CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor,

int procState, Bundle state, PersistableBundle persistentState,

List pendingResults, List pendingNewIntents,

boolean notResumed, boolean isForward, ProfilerInfo profilerInfo) \{

updateProcessState(procState, false);

ActivityClientRecord r = new ActivityClientRecord();

r.token = token;

r.ident = ident;

r.intent = intent;

r.referrer = referrer;

...

updatePendingConfiguration(curConfig);

sendMessage(H.LAUNCH\_ACTIVITY, r);

scheduleLaunchActivity方法会将启动Activity的参数封装成ActivityClientRecord ，sendMessage方法向H类发送类型为LAUNCH\_ACTIVITY的消息，并将ActivityClientRecord 传递过去，sendMessage方法有多个重载方法，最终调用的sendMessage方法如下所示。

frameworks/base/core/java/android/app/ActivityThread.java

private void sendMessage(int what, Object obj, int arg1, int arg2, boolean async) \{

if (DEBUG\_MESSAGES) Slog.v(

TAG, "SCHEDULE " + what + " " + mH.codeToString(what)

\+ ": " + arg1 + " / " + obj);

Message msg = Message.obtain();

msg.what = what;

msg.obj = obj;

msg.arg1 = arg1;

msg.arg2 = arg2;

if (async) \{

msg.setAsynchronous(true);

mH.sendMessage(msg);

这里mH指的是H，它是ActivityThread的内部类并继承Handler，是应用程序进程中主线程的消息管理类。H的代码如下所示。

private class H extends Handler \{

public static final int LAUNCH\_ACTIVITY = 100;

public static final int PAUSE\_ACTIVITY = 101;

...

public void handleMessage(Message msg) \{

if (DEBUG\_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));

switch (msg.what) \{

case LAUNCH\_ACTIVITY: \{

Trace.traceBegin(Trace.TRACE\_TAG\_ACTIVITY\_MANAGER, "activityStart");

final ActivityClientRecord r = (ActivityClientRecord) msg.obj;//1

r.packageInfo = getPackageInfoNoCheck(

r.activityInfo.applicationInfo, r.compatInfo);//2

handleLaunchActivity(r, null, "LAUNCH\_ACTIVITY");//3

Trace.traceEnd(Trace.TRACE\_TAG\_ACTIVITY\_MANAGER);

\} break;

case RELAUNCH\_ACTIVITY: \{

Trace.traceBegin(Trace.TRACE\_TAG\_ACTIVITY\_MANAGER, "activityRestart");

ActivityClientRecord r = (ActivityClientRecord)msg.obj;

handleRelaunchActivity(r);

Trace.traceEnd(Trace.TRACE\_TAG\_ACTIVITY\_MANAGER);

\} break;

...

查看H的handleMessage方法中对LAUNCH\_ACTIVITY的处理，在注释1处将传过来的msg的成员变量obj转换为ActivityClientRecord。

在注释2处通过getPackageInfoNoCheck方法获得LoadedApk类型的对象并赋值给ActivityClientRecord 的成员变量packageInfo 。应用程序进程要启动Activity时需要将该Activity所属的APK加载进来，而LoadedApk就是用来描述已加载的APK文件。

在注释3处调用handleLaunchActivity方法，代码如下所示。

frameworks/base/core/java/android/app/ActivityThread.java

private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) \{

...

WindowManagerGlobal.initialize();

//启动Activity

Activity a = performLaunchActivity(r, customIntent);//1

if (a != null) \{

r.createdConfig = new Configuration(mConfiguration);

reportSizeConfigurations(r);

Bundle oldState = r.state;

//将Activity的状态置为Resume

handleResumeActivity(r.token, false, r.isForward,

!r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);//2

if (!r.activity.mFinished && r.startsNotResumed) \{

performPauseActivityIfNeeded(r, reason);

if (r.isPreHoneycomb()) \{

r.state = oldState;

\} else \{

try \{

//停止Activity启动

ActivityManager.getService()

.finishActivity(r.token, Activity.RESULT\_CANCELED, null,

Activity.DONT\_FINISH\_TASK\_WITH\_ACTIVITY);

\} catch (RemoteException ex) \{

throw ex.rethrowFromSystemServer();

注释1处的performLaunchActivity方法用来启动Activity ，注释2处的代码用来将Activity 的状态置为Resume。如果该Activity为null则会通知AMS停止启动Activity。来查看performLaunchActivity方法做了什么：

frameworks/base/core/java/android/app/ActivityThread.java

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) \{

//获取ActivityInfo类

ActivityInfo aInfo = r.activityInfo;//1

if (r.packageInfo == null) \{

//获取APK文件的描述类LoadedApk

r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,

Context.CONTEXT\_INCLUDE\_CODE);//2

ComponentName component = r.intent.getComponent();//3

...

//创建要启动Activity的上下文环境

ContextImpl appContext = createBaseContextForActivity(r);//4

Activity activity = null;

try \{

java.lang.ClassLoader cl = appContext.getClassLoader();

//用类加载器来创建该Activity的实例

activity = mInstrumentation.newActivity(

cl, component.getClassName(), r.intent);//5

...

\} catch (Exception e) \{

...

try \{

//创建Application

Application app = r.packageInfo.makeApplication(false, mInstrumentation);//6

...

if (activity != null) \{

...

/\*\*

\*7 初始化Activity

\*/

activity.attach(appContext, this, getInstrumentation(), r.token,

r.ident, app, r.intent, r.activityInfo, title, r.parent,

r.embeddedID, r.lastNonConfigurationInstances, config,

r.referrer, r.voiceInteractor, window, r.configCallback);

...

if (r.isPersistable()) \{

mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);//8

\} else \{

mInstrumentation.callActivityOnCreate(activity, r.state);

...

r.paused = true;

mActivities.put(r.token, r);

\} catch (SuperNotCalledException e) \{

throw e;

\} catch (Exception e) \{

...

return activity;

注释1处用来获取ActivityInfo，ActivityInfo用于存储代码和AndroidManifes设置的Activity和receiver节点信息，比如Activity的theme和launchMode。在注释2处获取APK文件的描述类LoadedApk。注释3处获取要启动的Activity的ComponentName类，ComponentName类中保存了该Activity的包名和类名。注释4处用来创建要启动Activity的上下文环境。注释5处根据ComponentName中存储的Activity类名，用类加载器来创建该Activity的实例。注释6处用来创建Application，makeApplication方法内部会调用Application的onCreate方法。注释7处调用Activity的attach方法初始化Activity，attach方法中会创建Window对象(PhoneWindow)并与Activity自身进行关联。注释8处会调用Instrumentation的callActivityOnCreate方法来启动Activity，如下所示。

frameworks/base/core/java/android/app/Instrumentation.java

public void callActivityOnCreate(Activity activity, Bundle icicle,

PersistableBundle persistentState) \{

prePerformCreate(activity);

activity.performCreate(icicle, persistentState);//1

postPerformCreate(activity);

注释1处调用了Activity的performCreate方法，代码如下所示。

frameworks/base/core/java/android/app/Activity.java

final void performCreate(Bundle icicle, PersistableBundle persistentState) \{

restoreHasCurrentPermissionRequest(icicle);

onCreate(icicle, persistentState);

mActivityTransitionState.readState(icicle);

performCreateCommon();

performCreate方法中会调用Activity的onCreate方法，讲到这里，根Activity就启动了，即应用程序就启动了。

根Activity启动过程就讲到这里，下面我们来学习根Activity启动过程中涉及到的进程。

2. 根Activity启动过程中涉及的进程

在应用程序进程没有创建的情况下，根Activity启动过程中会涉及到4个进程，分别是Zygote进程、Launcher进程、AMS所在进程(SyetemServer进程)、应用程序进程。它们之间的关系如下图所示。

![d9d658807882][]

image.png

首先Launcher进程向AMS请求创建根Activity，AMS会判断根Activity所需的应用程序进程是否存在并启动，如果不存在就会请求Zygote进程创建应用程序进程。应用程序进程准备就绪后会通知AMS，AMS会请求应用程序进程创建根Activity。上图中步骤2采用的是Socket通信，步骤1和步骤4采用的是Binder通信。

上图可能并不是很直观，为了更好的理解，下面给出这四个进程调用的时序图。

![d9d658807882][]

image.png

如果是普通Activity启动过程会涉及到几个进程呢？答案是两个，AMS所在进程和应用程序进程。实际上理解了根Activity的启动过程(根Activity的onCreate过程)，根Activity和普通Activity其他生命周期状态比如onStart、onResume等过程也会很轻松的掌握，这些知识点都是触类旁通的，想要具体了解这些知识点的同学可以自行阅读源码。

[d9d658807882]: /images/20221005/92231d484f974d23b6964cbfdc4b3493.png