Activity 启动流程(二)

Android知识总结

一、Activity到AMS阶段(API28)


调用Activity.startActivity启动Activity

    public void startActivity(Intent intent) {
        this.startActivity(intent, null);
    }

    public void startActivity(Intent intent, @Nullable Bundle options) {
        if (options != null) {
            startActivityForResult(intent, -1, options);
        } else {
            //options 为空时执行， requestCode == -1
            startActivityForResult(intent, -1);
        }
    }
    public void startActivityForResult(@RequiresPermission Intent intent, int requestCode) {
        startActivityForResult(intent, requestCode, null);
    }

    public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
            @Nullable Bundle options) {
        if (mParent == null) {//mParent表示当前Activity的父类，一般为null
            options = transferSpringboardActivityOptions(options);
            //调用Instrumentation.execStartActivity()，启动新的Activity。
            //mMainThread类型为ActivityThread, 在attach()时被回调时被赋值。
            Instrumentation.ActivityResult ar =
                mInstrumentation.execStartActivity(
                    this, mMainThread.getApplicationThread(), mToken, this,
                    intent, requestCode, options);
            if (ar != null) {
                mMainThread.sendActivityResult(
                    mToken, mEmbeddedID, requestCode, ar.getResultCode(),
                    ar.getResultData());
            }
            if (requestCode >= 0) {
                mStartedActivity = true;
            }

            cancelInputsAndStartExitTransition(options);
            // TODO Consider clearing/flushing other event sources and events for child windows.
        } else {
            if (options != null) {
                mParent.startActivityFromChild(this, intent, requestCode, options);
            } else {
                // existing applications that may have overridden it.
                mParent.startActivityFromChild(this, intent, requestCode);
            }
        }
    }
    
    //启动 Activity
    public void startActivityFromChild(@NonNull Activity child, @RequiresPermission Intent intent,
            int requestCode, @Nullable Bundle options) {
        options = transferSpringboardActivityOptions(options);
        Instrumentation.ActivityResult ar =
            mInstrumentation.execStartActivity(
                this, mMainThread.getApplicationThread(), mToken, child,
                intent, requestCode, options);
        if (ar != null) {
            mMainThread.sendActivityResult(
                mToken, child.mEmbeddedID, requestCode,
                ar.getResultCode(), ar.getResultData());
        }
        cancelInputsAndStartExitTransition(options);
    }

当mInstrumentation.execStartActivity的返回结果不为空，执行ActivityThread.sendActivityResult方法

    public final void sendActivityResult(
            IBinder token, String id, int requestCode,
            int resultCode, Intent data) {
        if (DEBUG_RESULTS) Slog.v(TAG, "sendActivityResult: id=" + id
                + " req=" + requestCode + " res=" + resultCode + " data=" + data);
        ArrayList<ResultInfo> list = new ArrayList<ResultInfo>();
        list.add(new ResultInfo(id, requestCode, resultCode, data));
        final ClientTransaction clientTransaction = ClientTransaction.obtain(mAppThread, token);
        clientTransaction.addCallback(ActivityResultItem.obtain(list));
        try {
            mAppThread.scheduleTransaction(clientTransaction);
        } catch (RemoteException e) {
            // Local scheduling
        }
    }

    private class ApplicationThread extends IApplicationThread.Stub {
        @Override
        public void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
            ActivityThread.this.scheduleTransaction(transaction);
        }
    }

执行Instrumentation的execStartActivity方法

    public ActivityResult execStartActivity(
            Context who, IBinder contextThread, IBinder token, Activity target,
            Intent intent, int requestCode, Bundle options) {
        //将contextThread转成ApplicationThread
        IApplicationThread whoThread = (IApplicationThread) contextThread;
        Uri referrer = target != null ? target.onProvideReferrer() : null;
        if (referrer != null) {
            intent.putExtra(Intent.EXTRA_REFERRER, referrer);
        }
        if (mActivityMonitors != null) {
            synchronized (mSync) {
                final int N = mActivityMonitors.size();
                for (int i=0; i<N; i++) {
                    final ActivityMonitor am = mActivityMonitors.get(i);
                    ActivityResult result = null;
                    if (am.ignoreMatchingSpecificIntents()) {
                        result = am.onStartActivity(intent);
                    }
                    if (result != null) {
                        am.mHits++;
                        return result;
                    } else if (am.match(who, null, intent)) {
                        am.mHits++;
                        if (am.isBlocking()) {
                            return requestCode >= 0 ? am.getResult() : null;
                        }
                        break;
                    }
                }
            }
        }
        try {
            intent.migrateExtraStreamToClipData();
            intent.prepareToLeaveProcess(who);
            //实际上这里是通过AIDL来调用AMS的startActivity方法
            int result = ActivityManager.getService()
                .startActivity(whoThread, who.getBasePackageName(), intent,
                        intent.resolveTypeIfNeeded(who.getContentResolver()),
                        token, target != null ? target.mEmbeddedID : null,
                        requestCode, 0, null, options);
            //检查StartActivity的结果
            checkStartActivityResult(result, intent);
        } catch (RemoteException e) {
            throw new RuntimeException("Failure from system", e);
        }
        return null;
    }

ActivityManager对AMS进行管理

public class ActivityManager {
    //IActivityManager 为 AMS 的代理
    public static IActivityManager getService() {
        return IActivityManagerSingleton.get();
    }

    private static final Singleton<IActivityManager> IActivityManagerSingleton =
            new Singleton<IActivityManager>() {
                @Override
                protected IActivityManager create() {
                    //获取 Binder 对象
                    final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE);
                    final IActivityManager am = IActivityManager.Stub.asInterface(b);
                    return am;
                }
            };
}

调用ActivityManagerService.startActivity方法，AMS实现了IActivityManager类，这是第一次Activity和AMS的Binder通信。

public class ActivityManagerService extends IActivityManager.Stub
        implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
    @Override
    public final int startActivity(IApplicationThread caller, String callingPackage,
            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
        return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
                resultWho, requestCode, startFlags, profilerInfo, bOptions,
                UserHandle.getCallingUserId());
    }

    @Override
    public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId) {
        return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
                resultWho, requestCode, startFlags, profilerInfo, bOptions, userId,
                true /*validateIncomingUser*/);
    }

    public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId,
            boolean validateIncomingUser) {
        //检查调用者是否合
        enforceNotIsolatedCaller("startActivity");
        //检查调用者是否有权限执行操作
        userId = mActivityStartController.checkTargetUser(userId, validateIncomingUser,
                Binder.getCallingPid(), Binder.getCallingUid(), "startActivityAsUser");

        // TODO: Switch to user app stacks here.
        return mActivityStartController.obtainStarter(intent, "startActivityAsUser")
                .setCaller(caller)
                .setCallingPackage(callingPackage)
                .setResolvedType(resolvedType)
                .setResultTo(resultTo)
                .setResultWho(resultWho)
                .setRequestCode(requestCode)
                .setStartFlags(startFlags)
                .setProfilerInfo(profilerInfo)
                .setActivityOptions(bOptions)
                .setMayWait(userId)
                .execute();
    }
}

二、AMS到ApplicationThread阶段(API28)

AMS-->ApplicationThread流程看起来复杂好多了，实际上这里面就干了2件事：

  • 1、综合处理launchMode和Intent中的Flag标志位，并根据处理结果生成一个目标 Activity 的对象(ActivityRecord)。
  • 2、判断是否需要为目标Activity B创建一个新的进程(ProcessRecord)、新的任务栈(TaskRecord)。

从AMS中开始执行

public class ActivityManagerService extends IActivityManager.Stub
        implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
    @Override
    public final int startActivity(IApplicationThread caller, String callingPackage,
            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
        return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
                resultWho, requestCode, startFlags, profilerInfo, bOptions,
                UserHandle.getCallingUserId());
    }

    @Override
    public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId) {
        return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
                resultWho, requestCode, startFlags, profilerInfo, bOptions, userId,
                true /*validateIncomingUser*/);
    }

    public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId,
            boolean validateIncomingUser) {
        //检查调用者是否合法
        enforceNotIsolatedCaller("startActivity");
        
        userId = mActivityStartController.checkTargetUser(userId, validateIncomingUser,
                Binder.getCallingPid(), Binder.getCallingUid(), "startActivityAsUser");

        // TODO: Switch to user app stacks here.
        return mActivityStartController.obtainStarter(intent, "startActivityAsUser")
                .setCaller(caller)
                .setCallingPackage(callingPackage)
                .setResolvedType(resolvedType)
                .setResultTo(resultTo)
                .setResultWho(resultWho)
                .setRequestCode(requestCode)
                .setStartFlags(startFlags)
                .setProfilerInfo(profilerInfo)
                .setActivityOptions(bOptions)
                .setMayWait(userId)
                .execute();
    }
}

执行ActivityStarter中的中的方法

class ActivityStarter {
    int execute() {
        try {
            // TODO(b/64750076): Look into passing request directly to these methods to allow
            // for transactional diffs and preprocessing.
            if (mRequest.mayWait) {
                return startActivityMayWait(mRequest.caller, mRequest.callingUid,
                        mRequest.callingPackage, mRequest.intent, mRequest.resolvedType,
                        mRequest.voiceSession, mRequest.voiceInteractor, mRequest.resultTo,
                        mRequest.resultWho, mRequest.requestCode, mRequest.startFlags,
                        mRequest.profilerInfo, mRequest.waitResult, mRequest.globalConfig,
                        mRequest.activityOptions, mRequest.ignoreTargetSecurity, mRequest.userId,
                        mRequest.inTask, mRequest.reason,
                        mRequest.allowPendingRemoteAnimationRegistryLookup);
            } else {
                return startActivity(mRequest.caller, mRequest.intent, mRequest.ephemeralIntent,
                        mRequest.resolvedType, mRequest.activityInfo, mRequest.resolveInfo,
                        mRequest.voiceSession, mRequest.voiceInteractor, mRequest.resultTo,
                        mRequest.resultWho, mRequest.requestCode, mRequest.callingPid,
                        mRequest.callingUid, mRequest.callingPackage, mRequest.realCallingPid,
                        mRequest.realCallingUid, mRequest.startFlags, mRequest.activityOptions,
                        mRequest.ignoreTargetSecurity, mRequest.componentSpecified,
                        mRequest.outActivity, mRequest.inTask, mRequest.reason,
                        mRequest.allowPendingRemoteAnimationRegistryLookup);
            }
        } finally {
            onExecutionComplete();
        }
    }

    private int startActivityMayWait(IApplicationThread caller, int callingUid,
            String callingPackage, Intent intent, String resolvedType,
            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
            IBinder resultTo, String resultWho, int requestCode, int startFlags,
            ProfilerInfo profilerInfo, WaitResult outResult,
            Configuration globalConfig, SafeActivityOptions options, boolean ignoreTargetSecurity,
            int userId, TaskRecord inTask, String reason,
            boolean allowPendingRemoteAnimationRegistryLookup) {
            ...
            int res = startActivity(caller, intent, ephemeralIntent, resolvedType, aInfo, rInfo,
                    voiceSession, voiceInteractor, resultTo, resultWho, requestCode, callingPid,
                    callingUid, callingPackage, realCallingPid, realCallingUid, startFlags, options,
                    ignoreTargetSecurity, componentSpecified, outRecord, inTask, reason,
                    allowPendingRemoteAnimationRegistryLookup);
            ...
    }
}

经过startActivity最终会调用ActivityStarter.startActivityUnchecked

    private int startActivity(final ActivityRecord r, ActivityRecord sourceRecord,
                IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
                int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
                ActivityRecord[] outActivity) {
        int result = START_CANCELED;
        try {
            mService.mWindowManager.deferSurfaceLayout();
            result = startActivityUnchecked(r, sourceRecord, voiceSession, voiceInteractor,
                    startFlags, doResume, options, inTask, outActivity);
        } finally {
            final ActivityStack stack = mStartActivity.getStack();
            if (!ActivityManager.isStartResultSuccessful(result) && stack != null) {
                stack.finishActivityLocked(mStartActivity, RESULT_CANCELED,
                        null /* intentResultData */, "startActivity", true /* oomAdj */);
            }
            mService.mWindowManager.continueSurfaceLayout();
        }

        postStartActivityProcessing(r, result, mTargetStack);

        return result;
    }

    private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
            int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
            ActivityRecord[] outActivity) {
    ...
        mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity, mOptions);
    ...

    }

调用ActivityStackSupervisor类的resumeFocusedStackTopActivityLocked方法

    boolean resumeFocusedStackTopActivityLocked(
            ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {

        if (!readyToResume()) {
            return false;
        }

        if (targetStack != null && isFocusedStack(targetStack)) {
            return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
        }
        final ActivityRecord r = mFocusedStack.topRunningActivityLocked();
        if (r == null || !r.isState(RESUMED)) {
            mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
        } else if (r.isState(RESUMED)) {
            // Kick off any lingering app transitions form the MoveTaskToFront operation.
            mFocusedStack.executeAppTransition(targetOptions);
        }

        return false;
    }

调用ActivityStack类的resumeTopActivityUncheckedLocked方法

    boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
        if (mStackSupervisor.inResumeTopActivity) {
            // Don't even start recursing.
            return false;
        }

        boolean result = false;
        try {
            // Protect against recursion.
            mStackSupervisor.inResumeTopActivity = true;
            result = resumeTopActivityInnerLocked(prev, options);
            final ActivityRecord next = topRunningActivityLocked(true /* focusableOnly */);
            if (next == null || !next.canTurnScreenOn()) {
                checkReadyForSleep();
            }
        } finally {
            mStackSupervisor.inResumeTopActivity = false;
        }

        return result;
    }

    private boolean resumeTopActivityInnerLocked(ActivityRecord prev,ActivityOptions options) {
        //... 
        if (mResumedActivity != null) {
          if (DEBUG_STATES) Slog.d(TAG_STATES,
              "resumeTopActivityLocked: Pausing "+ mResumedActivity);
          //暂停当前activity，调用Activity的onPause
          pausing |= startPausingLocked(userLeaving,false, next, false);
       }
       //...     
      
        mStackSupervisor.startSpecificActivityLocked(next, true, true);//启动新activity
       //... 
    }

这个方法虽然是叫resume..., 但是在这之前需要先调用startPausingLocked方法将之前的A给暂停，因此在A中调用startActivity打开B时，实际上是先执行A的onPause方法，在执行B的onCreate生命周期。

然后又回到ActivityStackSupervisor调用startSpecificActivityLocked方法

    void startSpecificActivityLocked(ActivityRecord r,
            boolean andResume, boolean checkConfig) {
        // 获取ProcessRecord
        ProcessRecord app = mService.getProcessRecordLocked(r.processName,
                r.info.applicationInfo.uid, true);

        getLaunchTimeTracker().setLaunchTime(r);

        if (app != null && app.thread != null) {//进程存在
            try {
                if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 0
                        || !"android".equals(r.info.packageName)) {
                    app.addPackage(r.info.packageName, r.info.applicationInfo.longVersionCode,
                            mService.mProcessStats);
                }
                realStartActivityLocked(r, app, andResume, checkConfig);
                return;
            } catch (RemoteException e) {
                Slog.w(TAG, "Exception when starting activity "
                        + r.intent.getComponent().flattenToShortString(), e);
            }
        }
        //进程不存在，创建新的ProcessRecord
        mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
                "activity", r.intent.getComponent(), false, false, true);
    }

这个方法中，判断系统Activity B进程(ProcessRecord)是否正在运行, 如果是则继续执行realStartActivityLocked方法，否则会调用AMS的startProcessLocked方法创建进程。

调用ActivityStackSupervisor.realStartActivityLocked

    final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
            boolean andResume, boolean checkConfig) throws RemoteException {
    ...
        mService.getLifecycleManager().scheduleTransaction(clientTransaction);
    ...
    }

在AMS中获取ClientLifecycleManager对象，然后调用scheduleTransaction方法

    private final ClientLifecycleManager mLifecycleManager;

    ClientLifecycleManager getLifecycleManager() {
        return mLifecycleManager;
    }

class ClientLifecycleManager {
    void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
        final IApplicationThread client = transaction.getClient();
        transaction.schedule();
        if (!(client instanceof Binder)) {
            transaction.recycle();
        }
    }
}

然后执行ClientTransaction.schedule最终调用IApplicationThread.scheduleTransaction,最终回到ApplicationThread中执行scheduleTransaction

public class ClientTransaction implements Parcelable, ObjectPoolItem {
    private IApplicationThread mClient;

    public IApplicationThread getClient() {
        return mClient;
    }

    public void schedule() throws RemoteException {
        mClient.scheduleTransaction(this);
    }
}

三、ApplicationThread到Activity启动步骤(API28)

API28重构之后步骤
public class ActivityStackSupervisor extends ConfigurationContainer implements DisplayListener,
        RecentTasks.Callbacks {
    void startSpecificActivityLocked(ActivityRecord r,
            boolean andResume, boolean checkConfig) {
        // Is this activity's application already running?
        ProcessRecord app = mService.getProcessRecordLocked(r.processName,
                r.info.applicationInfo.uid, true);

        getLaunchTimeTracker().setLaunchTime(r);

        if (app != null && app.thread != null) {
            try {
                if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 0
                        || !"android".equals(r.info.packageName)) {
                    // separate apk in the process.
                    app.addPackage(r.info.packageName, r.info.applicationInfo.longVersionCode,
                            mService.mProcessStats);
                }
                realStartActivityLocked(r, app, andResume, checkConfig);
                return;
            } catch (RemoteException e) {
                Slog.w(TAG, "Exception when starting activity "
                        + r.intent.getComponent().flattenToShortString(), e);
            }
        }
        mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
                "activity", r.intent.getComponent(), false, false, true);
    }


    final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
                                          boolean andResume, boolean checkConfig) throws RemoteException {
        final ClientTransaction clientTransaction = ClientTransaction.obtain(app.thread,
                r.appToken);
        clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),
                System.identityHashCode(r), 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, app.repProcState, r.icicle,
                r.persistentState, results, newIntents, mService.isNextTransitionForward(),
                profilerInfo));

        // Set desired final state.
        final ActivityLifecycleItem lifecycleItem;
        if (andResume) {
            lifecycleItem = ResumeActivityItem.obtain(mService.isNextTransitionForward());
        } else {
            lifecycleItem = PauseActivityItem.obtain();
        }
        clientTransaction.setLifecycleStateRequest(lifecycleItem);

        //通过 ActivityManagerService 获取 ClientLifecycleManager
        mService.getLifecycleManager().scheduleTransaction(clientTransaction);
    }
}

调用ClientLifecycleManager.scheduleTransaction方法

class ClientLifecycleManager {
    void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
        final IApplicationThread client = transaction.getClient();
        transaction.schedule();
        if (!(client instanceof Binder)) {
            transaction.recycle();
        }
    }

    void scheduleTransaction(@NonNull IApplicationThread client, @NonNull IBinder activityToken,
            @NonNull ActivityLifecycleItem stateRequest) throws RemoteException {
        final ClientTransaction clientTransaction = transactionWithState(client, activityToken,
                stateRequest);
        scheduleTransaction(clientTransaction);
    }

    void scheduleTransaction(@NonNull IApplicationThread client, @NonNull IBinder activityToken,
            @NonNull ClientTransactionItem callback) throws RemoteException {
        final ClientTransaction clientTransaction = transactionWithCallback(client, activityToken,
                callback);
        scheduleTransaction(clientTransaction);
    }

    void scheduleTransaction(@NonNull IApplicationThread client,
            @NonNull ClientTransactionItem callback) throws RemoteException {
        final ClientTransaction clientTransaction = transactionWithCallback(client,
                null /* activityToken */, callback);
        scheduleTransaction(clientTransaction);
    }

    private static ClientTransaction transactionWithState(@NonNull IApplicationThread client,
            @NonNull IBinder activityToken, @NonNull ActivityLifecycleItem stateRequest) {
        final ClientTransaction clientTransaction = ClientTransaction.obtain(client, activityToken);
        clientTransaction.setLifecycleStateRequest(stateRequest);
        return clientTransaction;
    }

    private static ClientTransaction transactionWithCallback(@NonNull IApplicationThread client,
            IBinder activityToken, @NonNull ClientTransactionItem callback) {
        final ClientTransaction clientTransaction = ClientTransaction.obtain(client, activityToken);
        clientTransaction.addCallback(callback);
        return clientTransaction;
    }
}

调用ClientTransaction.schedule执行事务

public class ClientTransaction implements Parcelable, ObjectPoolItem {
    private IApplicationThread mClient;
    private IBinder mActivityToken;
    /** Get the target client of the transaction. */
    public IApplicationThread getClient() {
        return mClient;
    }

    //通过 mClient 也就是IApplicationThread跨进程调用到应用进程
    public void schedule() throws RemoteException {
        mClient.scheduleTransaction(this);
    }
}

在ActivityThread中调用IApplicationThread.Stub的AIDL的实现类ApplicationThread中的方法scheduleTransaction，

private class ApplicationThread extends IApplicationThread.Stub {
    ...
    @Override
    public void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
        ActivityThread.this.scheduleTransaction(transaction);
    }
}

调用ClientTransactionHandler的scheduleTransaction方法

public abstract class ClientTransactionHandler {

    // Schedule phase related logic and handlers.

    /** Prepare and schedule transaction for execution. */
    void scheduleTransaction(ClientTransaction transaction) {
        transaction.preExecute(this);
        sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);
    }
    abstract void sendMessage(int what, Object obj);
    ...
}

调用ClientTransactionHandler的实现类ActivityThread的sendMessage向Handler发送消息， ActivityThread实现ClientTransactionHandler的抽象方法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);
    }

private final TransactionExecutor mTransactionExecutor = new TransactionExecutor(this);

class H extends Handler {
    ...
    public static final int EXECUTE_TRANSACTION = 159;
    ...
    public void handleMessage(Message msg) {
     ...
       case EXECUTE_TRANSACTION:
            final ClientTransaction transaction = (ClientTransaction) msg.obj;
            mTransactionExecutor.execute(transaction);
            if (isSystem()) {
                  transaction.recycle();
    }
}

在ActivityThread的内部Handler实现类H中执行TransactionExecutor.execute事务

    public void execute(ClientTransaction transaction) {
        if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "Start resolving transaction");

        final IBinder token = transaction.getActivityToken();
        if (token != null) {
            final Map<IBinder, ClientTransactionItem> activitiesToBeDestroyed =
                    mTransactionHandler.getActivitiesToBeDestroyed();
            final ClientTransactionItem destroyItem = activitiesToBeDestroyed.get(token);
            if (destroyItem != null) {
                if (transaction.getLifecycleStateRequest() == destroyItem) {
                    // It is going to execute the transaction that will destroy activity with the
                    // token, so the corresponding to-be-destroyed record can be removed.
                    activitiesToBeDestroyed.remove(token);
                }
                if (mTransactionHandler.getActivityClient(token) == null) {
                    // The activity has not been created but has been requested to destroy, so all
                    // transactions for the token are just like being cancelled.
                    Slog.w(TAG, tId(transaction) + "Skip pre-destroyed transaction:\n"
                            + transactionToString(transaction, mTransactionHandler));
                    return;
                }
            }
        }

        if (DEBUG_RESOLVER) Slog.d(TAG, transactionToString(transaction, mTransactionHandler));
        //1
        executeCallbacks(transaction);

        executeLifecycleState(transaction);
        mPendingActions.clear();
        if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "End resolving transaction");
    }

TransactionExecutor.executeCallbacks

    public void executeCallbacks(ClientTransaction transaction) {
        final List<ClientTransactionItem> callbacks = transaction.getCallbacks();
        if (callbacks == null || callbacks.isEmpty()) {
            // No callbacks to execute, return early.
            return;
        }
        if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "Resolving callbacks in transaction");

        final IBinder token = transaction.getActivityToken();
        ActivityClientRecord r = mTransactionHandler.getActivityClient(token);

        final ActivityLifecycleItem finalStateRequest = transaction.getLifecycleStateRequest();
        final int finalState = finalStateRequest != null ? finalStateRequest.getTargetState()
                : UNDEFINED;
        // Index of the last callback that requests some post-execution state.
        final int lastCallbackRequestingState = lastCallbackRequestingState(transaction);

        final int size = callbacks.size();
        for (int i = 0; i < size; ++i) {
            final ClientTransactionItem item = callbacks.get(i);
            if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "Resolving callback: " + item);
            final int postExecutionState = item.getPostExecutionState();
            final int closestPreExecutionState = mHelper.getClosestPreExecutionState(r,
                    item.getPostExecutionState());
            if (closestPreExecutionState != UNDEFINED) {
                cycleToPath(r, closestPreExecutionState, transaction);
            }
            //2
            item.execute(mTransactionHandler, token, mPendingActions);
            item.postExecute(mTransactionHandler, token, mPendingActions);
            if (r == null) {
                // Launch activity request will create an activity record.
                r = mTransactionHandler.getActivityClient(token);
            }

            if (postExecutionState != UNDEFINED && r != null) {
                // Skip the very last transition and perform it by explicit state request instead.
                final boolean shouldExcludeLastTransition =
                        i == lastCallbackRequestingState && finalState == postExecutionState;
                cycleToPath(r, postExecutionState, shouldExcludeLastTransition, transaction);
            }
        }
    }

调用ClientTransactionItem的实现类LaunchActivityItem的execute方法

    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);
    }

调用ClientTransactionHandler的实现类ActivityThread的handleLaunchActivity方法

public Activity handleLaunchActivity(ActivityClientRecord r,
            PendingTransactionActions pendingActions, Intent customIntent) {
    ...
  final Activity a = performLaunchActivity(r, customIntent);
    ...
}

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
//获取Activity
activity = mInstrumentation.newActivity(
      cl, component.getClassName(), r.intent);
  ...
  //向Activity绑定数据
  //attach中会建立Activity与ContextImpl的联系
  //attach中还会创建Window并与Window建立联系 可以看Activivity中的源码
  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);
 } else {
    mInstrumentation.callActivityOnCreate(activity, r.state);
 }
...
}

执行Instrumentation类中的方法

    public void callActivityOnCreate(Activity activity, Bundle icicle) {
        prePerformCreate(activity);
        activity.performCreate(icicle);
        postPerformCreate(activity);
    }

    public void callActivityOnCreate(Activity activity, Bundle icicle,
            PersistableBundle persistentState) {
        prePerformCreate(activity);
        activity.performCreate(icicle, persistentState);
        postPerformCreate(activity);
    }

执行Activity的performCreate方法，进行创建

    final void performCreate(Bundle icicle) {
        performCreate(icicle, null);
    }

    @UnsupportedAppUsage
    final void performCreate(Bundle icicle, PersistableBundle persistentState) {
        dispatchActivityPreCreated(icicle);
        mCanEnterPictureInPicture = true;
        // initialize mIsInMultiWindowMode and mIsInPictureInPictureMode before onCreate
        final int windowingMode = getResources().getConfiguration().windowConfiguration
                .getWindowingMode();
        mIsInMultiWindowMode = inMultiWindowMode(windowingMode);
        mIsInPictureInPictureMode = windowingMode == WINDOWING_MODE_PINNED;
        restoreHasCurrentPermissionRequest(icicle);
        //创建 Activity
        if (persistentState != null) {
            onCreate(icicle, persistentState);
        } else {
            onCreate(icicle);
        }
        EventLogTags.writeWmOnCreateCalled(mIdent, getComponentName().getClassName(),
                "performCreate");
        mActivityTransitionState.readState(icicle);

        mVisibleFromClient = !mWindow.getWindowStyle().getBoolean(
                com.android.internal.R.styleable.Window_windowNoDisplay, false);
        mFragments.dispatchActivityCreated();
        mActivityTransitionState.setEnterActivityOptions(this, getActivityOptions());
        dispatchActivityPostCreated(icicle);
    }

三、API30 Activity启动的整体流程

Activity 启动流程.jpg
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