主要参考的源码为Android2.3与8.0，从姜饼到奥瑞奥，Activity的主要逻辑并没有根本性的改变，更多是做了一些封装和优化，下文会在版本变化中对相关变化的代码进行对比和说明。

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Launcher发送start请求

1 Launcher.startActivitySafely

系统启动时 PackageManagerService 解析 Androidmainfest文件， 会获取启动需要的laucher等信息，详情见《安卓源码分析与演变——PackageManager全流程》

之后根据flag走相应的启动流程

 public List queryIntentActivities(Intent intent,

            String resolvedType, int flags) {

        ComponentName comp = intent.getComponent();

        if (comp != null) {

            List list = new ArrayList(1);

            ActivityInfo ai = getActivityInfo(comp, flags);

            if (ai != null) {

                ResolveInfo ri = new ResolveInfo();

                ri.activityInfo = ai;

                list.add(ri);

            }

            return list;

        }

        synchronized (mPackages) {

            String pkgName = intent.getPackage();

            if (pkgName == null) {

                return (List)mActivities.queryIntent(intent,

                        resolvedType, flags);

            }

            PackageParser.Package pkg = mPackages.get(pkgName);

            if (pkg != null) {

                return (List) mActivities.queryIntentForPackage(intent,

                        resolvedType, flags, pkg.activities);

            }

            return null;

        }

    }

    void startActivitySafely(Intent intent, Object tag) {

        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

        try {

            startActivity(intent);

        } catch (ActivityNotFoundException e) {

            Toast.makeText(this, R.string.activity_not_found, Toast.LENGTH_SHORT).show();

            Log.e(TAG, "Unable to launch. tag=" + tag + " intent=" + intent, e);

        } catch (SecurityException e) {

            Toast.makeText(this, R.string.activity_not_found, Toast.LENGTH_SHORT).show();

            Log.e(TAG, "Launcher does not have the permission to launch " + intent +

                    ". Make sure to create a MAIN intent-filter for the corresponding activity " +

                    "or use the exported attribute for this activity. "

                    + "tag="+ tag + " intent=" + intent, e);

        }

    }

2 Activity.startActivity

  @Override

    public void startActivity(Intent intent) {

        startActivityForResult(intent, -1);

    }

3 startActivityForResult

Instrument 监护系统和应用交互

ActivityThread 每个应用进程启动持有，拥有ApplicationThread变量（Binder本地对象），作为参数传递给ActivityManagerService，通知组件进入

paused状态

Activity的mToken为Ibinder（代理对象），指向ActivityManagerService的ActivityRecord

 public void startActivityForResult(Intent intent, int requestCode) {

        if (mParent == null) {

            Instrumentation.ActivityResult ar =

                mInstrumentation.execStartActivity(

                    this, mMainThread.getApplicationThread(), mToken, this,

                    intent, requestCode);

            if (ar != null) {

                mMainThread.sendActivityResult(

                    mToken, mEmbeddedID, requestCode, ar.getResultCode(),

                    ar.getResultData());

            }

            if (requestCode >= 0) {

                // If this start is requesting a result, we can avoid making

                // the activity visible until the result is received.  Setting

                // this code during onCreate(Bundle savedInstanceState) or onResume() will keep the

                // activity hidden during this time, to avoid flickering.

                // This can only be done when a result is requested because

                // that guarantees we will get information back when the

                // activity is finished, no matter what happens to it.

                mStartedActivity = true;

            }

        } else {

            mParent.startActivityFromChild(this, intent, requestCode);

        }

    }

4 Instrument.execStartActivity

  public ActivityResult execStartActivity(

        Context who, IBinder contextThread, IBinder token, Activity target,

        Intent intent, int requestCode) {

        IApplicationThread whoThread = (IApplicationThread) contextThread;

        if (mActivityMonitors != null) {

            synchronized (mSync) {

                final int N = mActivityMonitors.size();

                for (int i=0; i
                    final ActivityMonitor am = mActivityMonitors.get(i);
                    if (am.match(who, null, intent)) {
                        am.mHits++;
                        if (am.isBlocking()) {
                            return requestCode >= 0 ? am.getResult() : null;
                        }
                        break;
                    }
                }
            }
        }
        try {
            int result = ActivityManagerNative.getDefault()
                .startActivity(whoThread, intent,
                        intent.resolveTypeIfNeeded(who.getContentResolver()),
                        null, 0, token, target != null ? target.mEmbeddedID : null,
                        requestCode, false, false);
            checkStartActivityResult(result, intent);
        } catch (RemoteException e) {
        }
        return null;
    }


版本变化
2.3版本
ActivityManagerNative.getDefalt获取ActivityManagerService的代理对象，封装为ActivityManagerProxy
 
  static public IActivityManager getDefault()
    {
        if (gDefault != null) {
            //if (Config.LOGV) Log.v(
            //    "ActivityManager", "returning cur default = " + gDefault);
            return gDefault;
        }
        IBinder b = ServiceManager.getService("activity");
        if (Config.LOGV) Log.v(
            "ActivityManager", "default service binder = " + b);
        gDefault = asInterface(b);
        if (Config.LOGV) Log.v(
            "ActivityManager", "default service = " + gDefault);
        return gDefault;
    }
8.0版本
 
int result = ActivityManager.getService()
                .startActivity(whoThread, who.getBasePackageName(), intent,
                        intent.resolveTypeIfNeeded(who.getContentResolver()),
                        token, target != null ? target.mEmbeddedID : null,
                        requestCode, 0, null, options);
取代了之前的ActivityManagerNative和proxy类，直接获取封装过的单例aidl接口IActivityManager，包括startservice等大量方法
调用asInterface()将服务端的Binder对象转换为客户端所需要的AIDL接口类型。如果客户端和服务端在同一个进程他返回的就是服务端Stub对象本身，否则返回封装的Stub.proxy对象。
 
private static final Singleton IActivityManagerSingleton =
            new Singleton() {
                @Override
                protected IActivityManager create() {
                    final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE);
                    final IActivityManager am = IActivityManager.Stub.asInterface(b);
                    return am;
                }
            };
//ServiceManager实质上是管理缓存的Ibinder对象
 public static IBinder getService(String name) {
        try {
            IBinder service = sCache.get(name);
            if (service != null) {
                return service;
            } else {
                return Binder.allowBlocking(getIServiceManager().getService(name));
            }
        } catch (RemoteException e) {
            Log.e(TAG, "error in getService", e);
        }
        return null;
    }

5 ActivityManagerNative.ActivityManagerProxy.startActivity
参数传递为Parcel，反序列化对象
通过ActivityManagerProxy的mRemote发送START_ACTIVITY_TRANSACTION，即进程间通信请求
（Proxy类实现IActivityManager接口，而8.0将中转的代理类去除，精简了流程）
 
public int startActivity(IApplicationThread caller, Intent intent,
            String resolvedType, Uri[] grantedUriPermissions, int grantedMode,
            IBinder resultTo, String resultWho,
            int requestCode, boolean onlyIfNeeded,
            boolean debug) throws RemoteException {
        Parcel data = Parcel.obtain();
        Parcel reply = Parcel.obtain();
        data.writeInterfaceToken(IActivityManager.descriptor);
        data.writeStrongBinder(caller != null ? caller.asBinder() : null);
        intent.writeToParcel(data, 0);
        data.writeString(resolvedType);
        data.writeTypedArray(grantedUriPermissions, 0);
        data.writeInt(grantedMode);
        data.writeStrongBinder(resultTo);
        data.writeString(resultWho);
        data.writeInt(requestCode);
        data.writeInt(onlyIfNeeded ? 1 : 0);
        data.writeInt(debug ? 1 : 0);
        mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);
        reply.readException();
        int result = reply.readInt();
        reply.recycle();
        data.recycle();
        return result;
    }

AMS处理start请求并发送paused
6 ActivityManagerService.startActivity
成员函数ActivityStack处理IPC请求，启动组件
 
 public final int startActivity(IApplicationThread caller,
            Intent intent, String resolvedType, Uri[] grantedUriPermissions,
            int grantedMode, IBinder resultTo,
            String resultWho, int requestCode, boolean onlyIfNeeded,
            boolean debug) {
        return mMainStack.startActivityMayWait(caller, intent, resolvedType,
                grantedUriPermissions, grantedMode, resultTo, resultWho,
                requestCode, onlyIfNeeded, debug, null, null);
    }

版本变化
8.0 使用了ActivityStarter，封装了ActivityStack、ActivityRecord、flag，intent相关的处理
 
 @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) {
        enforceNotIsolatedCaller("startActivity");
        userId = mUserController.handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(),
                userId, false, ALLOW_FULL_ONLY, "startActivity", null);
        // TODO: Switch to user app stacks here.
        return mActivityStarter.startActivityMayWait(caller, -1, callingPackage, intent,
                resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
                profilerInfo, null, null, bOptions, false, userId, null, null,
                "startActivityAsUser");
    }
7 ActivityStack.startActivityMayWait
解析intent信息
 
 final int startActivityMayWait(IApplicationThread caller,
            Intent intent, String resolvedType, Uri[] grantedUriPermissions,
            int grantedMode, IBinder resultTo,
            String resultWho, int requestCode, boolean onlyIfNeeded,
            boolean debug, WaitResult outResult, Configuration config) {
     ActivityInfo aInfo;
        try {
            ResolveInfo rInfo =
                AppGlobals.getPackageManager().resolveIntent(
                        intent, resolvedType,
                        PackageManager.MATCH_DEFAULT_ONLY
                        | ActivityManagerService.STOCK_PM_FLAGS);
            aInfo = rInfo != null ? rInfo.activityInfo : null;
        } catch (RemoteException e) {
            aInfo = null;
        }
...
    
            int res = startActivityLocked(caller, intent, resolvedType,
                    grantedUriPermissions, grantedMode, aInfo,
                    resultTo, resultWho, requestCode, callingPid, callingUid,
8 ActivityStack.startActivityLocked
ActivityManagerService获取Caller对应的Proce***ecord对象，该对象指向Launcher所在进程，获取pid和uid
从mHistory寻找ActivityRecord信息，保存变量sourceActivity

 

9 ActivityStack.startActivityUnCheckedLocked
判断标志位，是否新task，是否用户操作，根据taskAffinity属性判断新Activity的task组归属
重载方法startActivityLocked，加入栈顶，保存history
 
final int startActivityUncheckedLocked(ActivityRecord r,
            ActivityRecord sourceRecord, Uri[] grantedUriPermissions,
            int grantedMode, boolean onlyIfNeeded, boolean doResume) {
        final Intent intent = r.intent;
        final int callingUid = r.launchedFromUid;
        
        int launchFlags = intent.getFlags();
        
      
        ActivityRecord notTop = (launchFlags&Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP)
                != 0 ? r : null;

         // Should this be considered a new task?
        if (r.resultTo == null && !addingToTask
                && (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
            // todo: should do better management of integers.
            mService.mCurTask++;
            if (mService.mCurTask <= 0) {
                mService.mCurTask = 1;
            }
            r.task = new TaskRecord(mService.mCurTask, r.info, intent,
                    (r.info.flags&ActivityInfo.FLAG_CLEAR_TASK_ON_LAUNCH) != 0);
            if (DEBUG_TASKS) Slog.v(TAG, "Starting new activity " + r
                    + " in new task " + r.task);
            newTask = true;
            if (mMainStack) {
                mService.addRecentTaskLocked(r.task);
            }
            
        } else if (sourceRecord != null) {
            if (!addingToTask &&
                    (launchFlags&Intent.FLAG_ACTIVITY_CLEAR_TOP) != 0) {
10 ActivityStack.resumeTopActivityLocked
如果将要启动的Activity已经resume或者pause直接返回，否则通知进入pause状态准备启动
 
 final boolean resumeTopActivityLocked(ActivityRecord prev) {
        // Find the first activity that is not finishing.
        ActivityRecord next = topRunningActivityLocked(null);
...
        // If the top activity is the resumed one, nothing to do.
        if (mResumedActivity == next && next.state == ActivityState.RESUMED) {
            // Make sure we have executed any pending transitions, since there
            // should be nothing left to do at this point.
            mService.mWindowManager.executeAppTransition();
            mNoAnimActivities.clear();
            return false;
        }

        // If we are sleeping, and there is no resumed activity, and the top
        // activity is paused, well that is the state we want.
        if ((mService.mSleeping || mService.mShuttingDown)
                && mLastPausedActivity == next && next.state == ActivityState.PAUSED) {
            // Make sure we have executed any pending transitions, since there
            // should be nothing left to do at this point.
            mService.mWindowManager.executeAppTransition();
            mNoAnimActivities.clear();
            return false;
        }
        
        // The activity may be waiting for stop, but that is no longer
        // appropriate for it.
        mStoppingActivities.remove(next);
        mWaitingVisibleActivities.remove(next);

      
        
        // We need to start pausing the current activity so the top one
        // can be resumed...
        if (mResumedActivity != null) {
            if (DEBUG_SWITCH) Slog.v(TAG, "Skip resume: need to start pausing");
            startPausingLocked(userLeaving, false);
            return true;
        }

        ...
        }
版本变化
8.0
ActivityStackSupervisor封装了ActivityStack有关的方法
 
boolean resumeFocusedStackTopActivityLocked(
            ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
        if (targetStack != null && isFocusedStack(targetStack)) {
            return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
        }
        final ActivityRecord r = mFocusedStack.topRunningActivityLocked();
        if (r == null || r.state != RESUMED) {
            mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
        } else if (r.state == RESUMED) {
            // Kick off any lingering app transitions form the MoveTaskToFront operation.
            mFocusedStack.executeAppTransition(targetOptions);
        }
        return false;
    }
11 startPausingLocked
调用AMP通知主Activity，进入pause状态。延时发送handler超时消息
 
private final void startPausingLocked(boolean userLeaving, boolean uiSleeping) {
      
        ActivityRecord prev = mResumedActivity;
       ...
      
        if (prev.app != null && prev.app.thread != null) {
            if (DEBUG_PAUSE) Slog.v(TAG, "Enqueueing pending pause: " + prev);
            try {
                EventLog.writeEvent(EventLogTags.AM_PAUSE_ACTIVITY,
                        System.identityHashCode(prev),
                        prev.shortComponentName);
                prev.app.thread.schedulePauseActivity(prev, prev.finishing, userLeaving,
                        prev.configChangeFlags);
                if (mMainStack) {
                    mService.updateUsageStats(prev, false);
                }
            } catch (Exception e) {
                // Ignore exception, if process died other code will cleanup.
                Slog.w(TAG, "Exception thrown during pause", e);
                mPausingActivity = null;
                mLastPausedActivity = null;
            }
        } else {
            mPausingActivity = null;
            mLastPausedActivity = null;
        }
    ...
      
        if (mPausingActivity != null) {
        
            // Schedule a pause timeout in case the app doesn't respond.
            // We don't give it much time because this directly impacts the
            // responsiveness seen by the user.
            Message msg = mHandler.obtainMessage(PAUSE_TIMEOUT_MSG);
            msg.obj = prev;
            mHandler.sendMessageDelayed(msg, PAUSE_TIMEOUT);
            if (DEBUG_PAUSE) Slog.v(TAG, "Waiting for pause to complete...");
        } else {
            // This activity failed to schedule the
            // pause, so just treat it as being paused now.
            if (DEBUG_PAUSE) Slog.v(TAG, "Activity not running, resuming next.");
            resumeTopActivityLocked(null);
        }
    }
 
  case PAUSE_TIMEOUT_MSG: {
                    IBinder token = (IBinder)msg.obj;
                    // We don't at this point know if the activity is fullscreen,
                    // so we need to be conservative and assume it isn't.
                    Slog.w(TAG, "Activity pause timeout for " + token);
                    activityPaused(token, null, true);
                }
12 APN.ApplicationThreadProxy.scheduePauseActivity
    Ibinder发往Laucher组件（异步请求）
 
  
    public final void schedulePauseActivity(IBinder token, boolean finished,
            boolean userLeaving, int configChanges) throws RemoteException {
        Parcel data = Parcel.obtain();
        data.writeInterfaceToken(IApplicationThread.descriptor);
        data.writeStrongBinder(token);
        data.writeInt(finished ? 1 : 0);
        data.writeInt(userLeaving ? 1 :0);
        data.writeInt(configChanges);
        mRemote.transact(SCHEDULE_PAUSE_ACTIVITY_TRANSACTION, data, null,
                IBinder.FLAG_ONEWAY);
        data.recycle();
    }
Launcher进入Pause状态
以上过程都在Laucher完成
13 ApplicationThread.scedulePauseActivity
binder指向ActivityRecord
 
 public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
                ActivityInfo info, Bundle state, List pendingResults,
                List pendingNewIntents, boolean notResumed, boolean isForward) {
            ActivityClientRecord r = new ActivityClientRecord();

            r.token = token;
            r.ident = ident;
            r.intent = intent;
            r.activityInfo = info;
            r.state = state;

            r.pendingResults = pendingResults;
            r.pendingIntents = pendingNewIntents;

            r.startsNotResumed = notResumed;
            r.isForward = isForward;

            queueOrSendMessage(H.LAUNCH_ACTIVITY, r);
        }
14 ActivityThread.queueOrSendMessage
mH处理主线程pause操作
15 ActivityThread.handleMessage
16 ActivityThread.handlePauseActivity
通知Launcher 用户离开
通知Launcher onPause
queueWork wait数据写入（以备onResume恢复）
通知ActivityManagerService pause
 
private final void handlePauseActivity(IBinder token, boolean finished,
            boolean userLeaving, int configChanges) {
        ActivityClientRecord r = mActivities.get(token);
        if (r != null) {
            //Slog.v(TAG, "userLeaving=" + userLeaving + " handling pause of " + r);
            if (userLeaving) {
                performUserLeavingActivity(r);
            }

           &nbs            
            
                                

                    网站标题：追踪Android源码演变——Activity启动全流程                    

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