Android 面试总结 - Activity的启动流程(2)

@Override

public int startActivityAsUser(IApplicationThread caller, String callingPackage,

String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,

String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,

Bundle bOptions, int userId) {

return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,

resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions, userId,

true /validateIncomingUser/);

}

ActivityTaskManagerService#startActivityAsUser

private int startActivityAsUser(IApplicationThread caller, String callingPackage,

@Nullable String callingFeatureId, Intent intent, String resolvedType,

IBinder resultTo, String resultWho, int requestCode, int startFlags,

ProfilerInfo profilerInfo, Bundle bOptions, int userId, boolean validateIncomingUser) {

assertPackageMatchesCallingUid(callingPackage);

enforceNotIsolatedCaller(“startActivityAsUser”);

userId = getActivityStartController().checkTargetUser(userId, validateIncomingUser,

Binder.getCallingPid(), Binder.getCallingUid(), “startActivityAsUser”);

// TODO: Switch to user app stacks here.

return getActivityStartController().obtainStarter(intent, “startActivityAsUser”)

.setCaller(caller)

.setCallingPackage(callingPackage)

.setCallingFeatureId(callingFeatureId)

.setResolvedType(resolvedType)

.setResultTo(resultTo)

.setResultWho(resultWho)

.setRequestCode(requestCode)

.setStartFlags(startFlags)

.setProfilerInfo(profilerInfo)

.setActivityOptions(bOptions)

.setUserId(userId)

.execute();

}

最后 return 的对象设置了那么多属性并在最后调用 excute() 执行。

return getActivityStartController().obtainStarter(intent, “startActivityAsUser”)

.setCaller(caller)

.setCallingPackage(callingPackage)

.setCallingFeatureId(callingFeatureId)

.setResolvedType(resolvedType)

.setResultTo(resultTo)

.setResultWho(resultWho)

.setRequestCode(requestCode)

.setStartFlags(startFlags)

.setProfilerInfo(profilerInfo)

.setActivityOptions(bOptions)

.setUserId(userId)

.execute();

先看看 getActivityStartController() 是个啥

ActivityStartController getActivityStartController() {

return mActivityStartController;

}

getActivityStartController().obtainStarter(intent, “startActivityAsUser”)

ActivityStarter obtainStarter(Intent intent, String reason) {

return mFactory.obtain().setIntent(intent).setReason(reason);

}

mFactory.obtain() 使用工厂模式从 DefaultFactory 类的缓存池(最大缓存数量为3) 中取出 ActivityStarter 对象

getActivityStartController().obtainStarter(intent, “startActivityAsUser”)

.setCaller(caller)

setCaller(caller) caller 是 IApplicationThread 类型的对象，等于 ActivityStarter 里缓存了与 app 进程连接的桥梁，之后可以进行跨进程调用 app 进程。

ApplicationThread是ActivityThread内部类，继承自IApplicationThread.Stub，作为服务端接受AMS发出的请求并执行，ApplicationThread是ActivityThread与AMS连接的桥梁。

再看最后的 execute()

return getActivityStartController().obtainStarter(intent, “startActivityAsUser”)

.setCaller(caller)

…

.execute();

ActivityStarter#execute

int execute() {

try {

…

res = executeRequest(mRequest);

…

return getExternalResult(mRequest.waitResult == null ? res

waitForResult(res, mLastStartActivityRecord));

} finally {

onExecutionComplete();

}

}

ActivityStarter#executeRequest

/**

*执行活动启动请求，开始启动活动的旅程。在这里

*首先执行几个初步检查。正常的活动启动流程将

*通过{@link#startActivityUnchecked}到{@link#startactivitynner}。

*/

private int executeRequest(Request request) {

…

// 在这里创建 ActivityRecord 对象，用于描述 Activity 信息

final ActivityRecord r = new ActivityRecord(mService, callerApp, callingPid, callingUid,

callingPackage, callingFeatureId, intent, resolvedType, aInfo,

mService.getGlobalConfiguration(), resultRecord, resultWho, requestCode,

request.componentSpecified, voiceSession != null, mSupervisor, checkedOptions,

sourceRecord);

…

mLastStartActivityResult = startActivityUnchecked(r, sourceRecord, voiceSession,

request.voiceInteractor, startFlags, true /* doResume */, checkedOptions, inTask,

restrictedBgActivity, intentGrants);

…

return mLastStartActivityResult;

}

ActivityStarter#startActivityUnchecked

private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,

IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,

int startFlags, boolean doResume, ActivityOptions options, Task inTask,

boolean restrictedBgActivity, NeededUriGrants intentGrants) {

int result = START_CANCELED;

final ActivityStack startedActivityStack;

try {

mService.deferWindowLayout();

Trace.traceBegin(Trace.TRACE_TAG_WINDOW_MANAGER, “startActivityInner”);

// 关键

result = startActivityInner(r, sourceRecord, voiceSession, voiceInteractor,

startFlags, doResume, options, inTask, restrictedBgActivity, intentGrants);

} finally {

Trace.traceEnd(Trace.TRACE_TAG_WINDOW_MANAGER);

startedActivityStack = handleStartResult(r, result);

mService.continueWindowLayout();

}

postStartActivityProcessing(r, result, startedActivityStack);

return result;

}

ActivityStarter#startActivityInner

int startActivityInner(final ActivityRecord r, ActivityRecord sourceRecord,

IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,

int startFlags, boolean doResume, ActivityOptions options, Task inTask,

boolean restrictedBgActivity, NeededUriGrants intentGrants) {

…

mRootWindowContainer.resumeFocusedStacksTopActivities(

mTargetStack, mStartActivity, mOptions);

…

return START_SUCCESS;

}

调用了RootWindowContainer#resumeFocusedStacksTopActivities

boolean resumeFocusedStacksTopActivities(

ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {

…

result |= focusedStack.resumeTopActivityUncheckedLocked(target, targetOptions);

…

return result;

}

调用 ActivityStack#resumeTopActivityUncheckedLocked

boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {

…

result = resumeTopActivityInnerLocked(prev, options);

…

return result;

}

private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {

…

//关键关键！！！ 传入了 next.app.getThread() 返回的是 IApplication

final ClientTransaction transaction =

ClientTransaction.obtain(next.app.getThread(), next.appToken);

transaction.setLifecycleStateRequest(

ResumeActivityItem.obtain(next.app.getReportedProcState(),

dc.isNextTransitionForward()));

mAtmService.getLifecycleManager().scheduleTransaction(transaction);

…

return true;

}

mStackSupervisor.startSpecificActivity(next, true, true);

ActivityStackSupervisor#startSpecificActivity

void startSpecificActivity(ActivityRecord r, boolean andResume, boolean checkConfig) {

…

realStartActivityLocked(r, wpc, andResume, checkConfig);

…

}

ActivityStackSupervisor#realStartActivityLocked

boolean realStartActivityLocked(ActivityRecord r, WindowProcessController proc,

boolean andResume, boolean checkConfig) throws RemoteException {

…

// Create activity launch transaction.

// 关键关键！！！ 传入了 proc.getThread() 返回的是 IApplication

// 赋值给 ClientTransaction 的 mClient 对象

final ClientTransaction clientTransaction = ClientTransaction.obtain(

proc.getThread(), r.appToken);

final DisplayContent dc = r.getDisplay().mDisplayContent;

clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),

System.identityHashCode®, r.info,

// TODO: Have this take the merged configuration instead of separate global

// and override configs.

mergedConfiguration.getGlobalConfiguration(),

mergedConfiguration.getOverrideConfiguration(), r.compat,

r.launchedFromPackage, task.voiceInteractor, proc.getReportedProcState(),

r.getSavedState(), r.getPersistentSavedState(), results, newIntents,

dc.isNextTransitionForward(), proc.createProfilerInfoIfNeeded(),

r.assistToken, r.createFixedRotationAdjustmentsIfNeeded()));

// Set desired final state.

final ActivityLifecycleItem lifecycleItem;

if (andResume) {

lifecycleItem = ResumeActivityItem.obtain(dc.isNextTransitionForward());

} else {

lifecycleItem = PauseActivityItem.obtain();

}

clientTransaction.setLifecycleStateRequest(lifecycleItem);

// Schedule transaction.

mService.getLifecycleManager().scheduleTransaction(clientTransaction);

…

}

通过缓存池获取 ClientTransaction 类型的对象，并通过 mService.getLifecycleManager()调用 scheduleTransaction 方法开始执行任务

mService 是 ActivityTaskManagerService 类型的对象

ActivityTaskManagerService#getLifecycleManager

ClientLifecycleManager getLifecycleManager() {

return mLifecycleManager;

}

返回的 ClientLifecycleManager 类型对象，再看它的 scheduleTransaction 做了啥

void scheduleTransaction(ClientTransaction transaction) throws RemoteException {

final IApplicationThread client = transaction.getClient();

transaction.schedule();

if (!(client instanceof Binder)) {

// If client is not an instance of Binder - it’s a remote call and at this point it is

// safe to recycle the object. All objects used for local calls will be recycled after

// the transaction is executed on client in ActivityThread.

transaction.recycle();

}

}

调用了 ClientTransaction 的 schedule 方法，简单粗暴。。。

要我们回头看 ClientTransaction 的 schedule 是怎么执行的

ATMS 进程切回 app 进程

public void schedule() throws RemoteException {

mClient.scheduleTransaction(this);

}

咦 又调用了 mClient 的 scheduleTransaction 。。。 额绕了一圈

又要回头看看 mClient 对象是啥了

在 ClientTransaction 中 mClient 是这样定义的

/** Target client. */

private IApplicationThread mClient;

IApplicationThread 对象 是与 app 进程沟通的桥梁！

刚刚在 调用 ActivityStack#resumeTopActivityUncheckedLocked 中将 IApplicationThread 传进 ClientTransaction 里了呢。

所以转了一圈 这个 ClientTransaction 对象会在 IApplicationThread 中调用，

同学们应该了解过 app 进程的 ApplicationThread 是 ActivityThread 内部类，并且实现了 IApplicationThread.Stub 。

mClient.scheduleTransaction(this); 实际上是 ApplicationThread#scheduleTransaction

这时候发生了跨进程：从 SystemServer 进程到 app 进程

ApplicationThread#scheduleTransaction

@Override

public void scheduleTransaction(ClientTransaction transaction) throws RemoteException {

ActivityThread.this.scheduleTransaction(transaction);

}

内部调用了 ActivityThread#scheduleTransaction

追代码发现 ActivityThread 并没有 scheduleTransaction 方法的具体实现，这时候需要看看 ActivityThread 的父类有没有

ActivityThread 继承了 ClientTransactionHandler

在 ClientTransactionHandler 中找到了 scheduleTransaction

void scheduleTransaction(ClientTransaction transaction) {

transaction.preExecute(this);

sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);

}

调用 sendMessage 方法并且 what 的值为 ActivityThread.H.EXECUTE_TRANSACTION

ClientTransactionHandler#sendMessage

abstract void sendMessage(int what, Object obj);

sendMessage 是抽象方法，找找在 ActivityThread 的具体实现

ActivityThread#sendMessage

void sendMessage(int what, Object obj) {

sendMessage(what, obj, 0, 0, false);

}

private void sendMessage(int what, Object obj, int arg1) {

sendMessage(what, obj, arg1, 0, false);

}

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

sendMessage(what, obj, arg1, arg2, false);

}

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);

}

private void sendMessage(int what, Object obj, int arg1, int arg2, int seq) {

if (DEBUG_MESSAGES) Slog.v(

TAG, “SCHEDULE " + mH.codeToString(what) + " arg1=” + arg1 + " arg2=" + arg2 +

"seq= " + seq);

Message msg = Message.obtain();

msg.what = what;

SomeArgs args = SomeArgs.obtain();

args.arg1 = obj;

args.argi1 = arg1;

args.argi2 = arg2;

args.argi3 = seq;

msg.obj = args;

mH.sendMessage(msg);

}

有一系列的重载方法，但最终都是调用 mH.sendMessage

final H mH = new H();

H 是 ActivityThread 的内部类，继承了 Handler

class H extends Handler

那刚刚 mH.sendMessage 发送的消息 ActivityThread.H.EXECUTE_TRANSACTION 会被 H 来处理

ActivityThread#H#handleMessage

public void handleMessage(Message msg) {

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

switch (msg.what) {

…

case EXECUTE_TRANSACTION:

final ClientTransaction transaction = (ClientTransaction) msg.obj;

mTransactionExecutor.execute(transaction);

if (isSystem()) {

// Client transactions inside system process are recycled on the client side

// instead of ClientLifecycleManager to avoid being cleared before this

// message is handled.

transaction.recycle();

}

// TODO(lifecycler): Recycle locally scheduled transactions.

break;

…

}

}

调用 TransactionExecutor 的 execute

public void execute(ClientTransaction transaction) {

…

executeCallbacks(transaction);

…

}

TransactionExecutor#executeCallbacks

/** Cycle through all states requested by callbacks and execute them at proper times. */

@VisibleForTesting

public void executeCallbacks(ClientTransaction transaction) {

// Callback 在 ActivityStackSupervisor#realStartActivityLocked中被添加 类型为 LaunchActivityItem

final List callbacks = transaction.getCallbacks();

if (callbacks == null || callbacks.isEmpty()) {

// No callbacks to execute, return early.

return;

}

final IBinder token = transaction.getActivityToken();

ActivityClientRecord r = mTransactionHandler.getActivityClient(token);

…

final int size = callbacks.size();

for (int i = 0; i < size; ++i) {

final ClientTransactionItem item = callbacks.get(i);

…

item.execute(mTransactionHandler, token, mPendingActions);

item.postExecute(mTransactionHandler, token, mPendingActions);

…

}

}

所以在这里执行的是 LaunchActivityItem 的 execute

LaunchActivityItem#execute

@Override

public void execute(ClientTransactionHandler client, IBinder token,

PendingTransactionActions pendingActions) {

Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, “activityStart”);

ActivityClientRecord r = new ActivityClientRecord(token, mIntent, mIdent, mInfo,

mOverrideConfig, mCompatInfo, mReferrer, mVoiceInteractor, mState, mPersistentState,

mPendingResults, mPendingNewIntents, mIsForward,

mProfilerInfo, client, mAssistToken, mFixedRotationAdjustments);

client.handleLaunchActivity(r, pendingActions, null /* customIntent */);

Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);

}

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自我介绍一下，小编13年上海交大毕业，曾经在小公司待过，也去过华为、OPPO等大厂，18年进入阿里一直到现在。**

深知大多数初中级Android工程师，想要提升技能，往往是自己摸索成长或者是报班学习，但对于培训机构动则近万的学费，着实压力不小。自己不成体系的自学效果低效又漫长，而且极易碰到天花板技术停滞不前！

因此收集整理了一份《2024年Android移动开发全套学习资料》，初衷也很简单，就是希望能够帮助到想自学提升又不知道该从何学起的朋友，同时减轻大家的负担。

[外链图片转存中…(img-ogA8Ekp0-1713203197740)]

[外链图片转存中…(img-odmTNVpY-1713203197743)]

[外链图片转存中…(img-KVy8B2LT-1713203197744)]

[外链图片转存中…(img-laY1Hriq-1713203197745)]

[外链图片转存中…(img-FGlDyGgI-1713203197746)]

既有适合小白学习的零基础资料，也有适合3年以上经验的小伙伴深入学习提升的进阶课程，基本涵盖了95%以上Android开发知识点，真正体系化！

由于文件比较大，这里只是将部分目录截图出来，每个节点里面都包含大厂面经、学习笔记、源码讲义、实战项目、讲解视频，并且会持续更新！

如果你觉得这些内容对你有帮助，可以扫码获取！！（备注：Android）

最后

我这里整理了一份完整的学习思维以及Android开发知识大全PDF。

[外链图片转存中…(img-g39eyF9c-1713203197747)]

当然实践出真知，即使有了学习线路也要注重实践，学习过的内容只有结合实操才算是真正的掌握。

《互联网大厂面试真题解析、进阶开发核心学习笔记、全套讲解视频、实战项目源码讲义》点击传送门即可获取！