前面梳理了WM中Window容器的概念，今天梳理一下startActivity的流程，看一下window容器的体现。
其实在server端Window最终都会表现为WindowState对象。而之所以存在划分层级的window容器，是为了有层级的管理，目的是实现Android的一些列feature，如：
- 任务栈Task，Task引出Activity的生命周期
- window focus，这个对于input子系统很重要
- 多Display支持
- 多Window支持
1、时序
# 1
Activity.startActivity
Activity.startActivityForResult
Instrumentation.execStartActivity
ActivityTaskManagerService.startActivity
ActivityTaskManagerService.startActivityAsUser
ActivityStarter.execute ->
# 2
->
ActivityStarter.execute
Request.resolveActivity
ActivityTaskSupervisor.resolveIntent
ActivityTaskSupervisor.resolveActivity
RootWindowContainer.getTopDisplayFocusedRootTask
ActivityStarter.executeRequest
ActivityStarter.startActivityUnchecked
ActivityStarter.startActivityInner
ActivityStarter.setInitialState
ActivityStarter.computeLaunchingTaskFlags
ActivityStarter.computeSourceRootTask
Task.startActivityLocked
RootWindowContainer.resumeFocusedTasksTopActivities
Task.resumeTopActivityUncheckedLocked
Task.resumeTopActivityInnerLocked
ActivityTaskSupervisor.startSpecificActivity
ActivityTaskSupervisor.realStartActivityLocked
ClientLifecycleManager.scheduleTransaction ->
# 3
->
ClientLifecycleManager.scheduleTransaction
ClientTransaction.schedule
ApplicationThread.scheduleTransaction
ClientTransactionHandler.scheduleTransaction // 具体实现是 ActivityThread
ActivityThread.H.handleMessage
TransactionExecutor.execute
TransactionExecutor.executeCallbacks
TransactionExecutor.cycleToPath
TransactionExecutor.performLifecycleSequence
ActivityThread.handleLaunchActivity ->
# 4
->
ActivityThread.handleLaunchActivity
ActivityThread.performLaunchActivity
Instrumentation.newActivity // new 一个 Activity
AppComponentFactory.instantiateActivity
LoadedApk.makeApplication
Instrumentation.newApplication
Instrumentation.callApplicationOnCreate
Activity.attach // Activity初始化
FragmentController.attachHost
new PhoneWindow // new 一个 PhoneWindow，其中会填充DecorView，DecorView是在onResume时，
// 在Activity.makeVisible方法中被addView的
Window.setWindowManager
Instrumentation.callActivityOnCreate
Activity.performCreate
Activity.onCreate // 回调 onCreate
分阶段说明
-
app端发起startActivity的请求，system server会将请求交给ATMS处理，然后由ActivityStarter执行
-
server端start Activity具体流程，包括：
- 解析Intent
- 处理launch flags，对应app端的launch mode
- 权限校验
- 按照Window层级，最终使Task去执行start Activity
- server处理好后，通过Binder通知app端执行相应业务
-
Binder通信：通过IApplicationThread（app实现，server调用它的代理）接口通知app端launch Activity。
app/server之间，Activity各个生命周期的通信都封装成了事务处理的工具类，传递的对象是ClientTransaction，
两端分别是server的ClientLifecycleManager 和 app的ClientTransactionHandler -
app端执行launch Activity，包括：
- new Activity，并初始化
- （如果没有创建Application）new Application，并回调其onCreate方法
- 回调Activity的onCreate
2、核心代码摘要
// ActivityStarter.java
private int executeRequest(Request request) {
final IBinder resultTo = request.resultTo;
// AM通过ProcessRecord管理进程。
// WM为例管理windows&activities，需要知道进程信息，WindowProcessController负责将AM端的进程信息、状态传递给WM。
// 获取caller信息，后面的校验&startActivity等需要caller的信息。
WindowProcessController callerApp = null;
if (caller != null) {
callerApp = mService.getProcessController(caller);
if (callerApp != null) {
callingPid = callerApp.getPid();
callingUid = callerApp.mInfo.uid;
} else {
Slog.w(TAG, "Unable to find app for caller " + caller + " (pid=" + callingPid
+ ") when starting: " + intent.toString());
err = ActivityManager.START_PERMISSION_DENIED;
}
}
ActivityRecord sourceRecord = null;
ActivityRecord resultRecord = null;
if (resultTo != null) {
sourceRecord = mRootWindowContainer.isInAnyTask(resultTo);
if (DEBUG_RESULTS) {
Slog.v(TAG_RESULTS, "Will send result to " + resultTo + " " + sourceRecord);
}
if (sourceRecord != null) {
if (requestCode >= 0 && !sourceRecord.finishing) {
resultRecord = sourceRecord;
}
}
}
// 处理 launch flags
final int launchFlags = intent.getFlags();
......
// 权限检查
boolean abort = !mSupervisor.checkStartAnyActivityPermission(intent, aInfo, resultWho,
requestCode, callingPid, callingUid, callingPackage, callingFeatureId,
request.ignoreTargetSecurity, inTask != null, callerApp, resultRecord,
resultRootTask);
abort |= !mService.mIntentFirewall.checkStartActivity(intent, callingUid,
callingPid, resolvedType, aInfo.applicationInfo);
abort |= !mService.getPermissionPolicyInternal().checkStartActivity(intent, callingUid,
callingPackage);
final ActivityRecord r = new ActivityRecord.Builder(mService)
.setCaller(callerApp)
......
.setSourceRecord(sourceRecord)
.build();
// 实际 startActivity
mLastStartActivityResult = startActivityUnchecked(r, sourceRecord, voiceSession,
request.voiceInteractor, startFlags, true /* doResume */, checkedOptions, inTask,
restrictedBgActivity, intentGrants);
return mLastStartActivityResult;
}
// ActivityStarter.java
// 通知RootWindowContainer和Task等容器处理之前的逻辑
int startActivityInner(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, Task inTask,
boolean restrictedBgActivity, NeededUriGrants intentGrants) {
setInitialState(r, options, inTask, doResume, startFlags, sourceRecord, voiceSession,
voiceInteractor, restrictedBgActivity);
computeLaunchingTaskFlags();
computeSourceRootTask();
......
mTargetRootTask.startActivityLocked(mStartActivity,
topRootTask != null ? topRootTask.getTopNonFinishingActivity() : null, newTask,
mKeepCurTransition, mOptions, sourceRecord);
......
mRootWindowContainer.resumeFocusedTasksTopActivities(
mTargetRootTask, mStartActivity, mOptions, mTransientLaunch);
......
}
private void setInitialState(ActivityRecord r, ActivityOptions options, Task inTask,
boolean doResume, int startFlags, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
boolean restrictedBgActivity) {
// 计算task边界？
// Preferred display id is the only state we need for now and it could be updated again
// after we located a reusable task (which might be resided in another display).
mSupervisor.getLaunchParamsController().calculate(inTask, r.info.windowLayout, r,
sourceRecord, options, mRequest, PHASE_DISPLAY, mLaunchParams);
// 获取TaskDisplayArea
mPreferredTaskDisplayArea = mLaunchParams.hasPreferredTaskDisplayArea()
? mLaunchParams.mPreferredTaskDisplayArea
: mRootWindowContainer.getDefaultTaskDisplayArea();
mPreferredWindowingMode = mLaunchParams.mWindowingMode;
mInTask = inTask;
}
private void computeLaunchingTaskFlags() {
// mInTask 是即将被添加ActivityRecord的Task
// 目的是初始化mAddingToTask
if (mSourceRecord == null && mInTask != null && mInTask.getRootTask() != null) {
} else {
}
if (mInTask == null) {
// 根据不同的情况，添加new task的标记位。
mLaunchFlags |= FLAG_ACTIVITY_NEW_TASK;
}
}