ActivityManagerService Activity的启动流程
简述
提到ActivityManagerService，最重要的流程之一就是启动Activity了。
这个流程比较复杂：
- 启动activity的调用链很长。
- 业务逻辑很多，activity启动有很多flag，例如FLAG_ACTIVITY_NEW_TASK，FLAG_ACTIVITY_CLEAR_TOP等等。
- 需要在app进程和systemserver之间来回binder调用。
同时activity启动还有两种不同的情况，一种是要启动的Activity进程已经存在了，只是新启动一个Activity，例如在app内部页面跳转。而另一种是要启动的Activity进程不存在，需要新启动一个进程，比如从桌面启动一个进程。
app启动Activity
1.1 Activity.startActivityForResult
Activity.startActivity最终也会走到Activity.startActivityForResult,只不过requestCode会传-1,我们就从这里开始.
这里的mParent是历史版本的遗留产物，应该是被Fragment替代了，这里可以不用管。
调用了Instrumentation.execStartActivity
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
@Nullable Bundle options) {
if (mParent == null) {
options = transferSpringboardActivityOptions(options);
// 调用Instrumentation.execStartActivity,详见1.2
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);
} else {
// ...
}
}1.2 Instrumentation.execStartActivity
mActivityMonitors一般用于CTS测试，除了mActivityMonitors插桩的逻辑，主要逻辑是调用ATMS服务，启动Activity
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
Uri referrer = target != null ? target.onProvideReferrer() : null;
if (referrer != null) {
intent.putExtra(Intent.EXTRA_REFERRER, referrer);
}
// ...mActivityMonitors,一般用于CTS测试
try {
intent.migrateExtraStreamToClipData(who);
intent.prepareToLeaveProcess(who);
// 调用ATMS启动activity，详见1.3
int result = ActivityTaskManager.getService().startActivity(whoThread,
who.getOpPackageName(), who.getAttributionTag(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()), token,
target != null ? target.mEmbeddedID : null, requestCode, 0, null, options);
// 通知mActivityMonitors返回结果
notifyStartActivityResult(result, options);
// 处理返回值，如果没有启动成功抛出对应异常
checkStartActivityResult(result, intent);
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
return null;
}1.3 ActivityTaskManagerService.startActivity
直接调用了startActivityAsUser
public final int startActivity(IApplicationThread caller, String callingPackage,
String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,
String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,
Bundle bOptions) {
// 详见1.4
return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions,
UserHandle.getCallingUserId());
}1.4 ActivityTaskManagerService.startActivityAsUser
调用了重载函数startActivityAsUser
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*/);
}1.5 ActivityTaskManagerService.startActivityAsUser
使用所有参数构造一个ActivityStarter，然后调用ActivityStarter.execute
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) {
final SafeActivityOptions opts = SafeActivityOptions.fromBundle(bOptions);
assertPackageMatchesCallingUid(callingPackage);
enforceNotIsolatedCaller("startActivityAsUser");
// ...
userId = getActivityStartController().checkTargetUser(userId, validateIncomingUser,
Binder.getCallingPid(), Binder.getCallingUid(), "startActivityAsUser");
// 详见1.6
return getActivityStartController().obtainStarter(intent, "startActivityAsUser")
.setCaller(caller) // 调用者对应的binder token
.setCallingPackage(callingPackage) // 调用者包名
.setCallingFeatureId(callingFeatureId)
.setResolvedType(resolvedType) // MIME类型
.setResultTo(resultTo) // startActivityForResult里接受返回结果的Activity
.setResultWho(resultWho)
.setRequestCode(requestCode) // startActivityForResult里面的requestCode
.setStartFlags(startFlags) // 启动的flag
.setProfilerInfo(profilerInfo)
.setActivityOptions(opts) // 启动Activity的option
.setUserId(userId) // 设置userId
.execute(); // 详见1.6
}1.6 ActivityStarter.execute
主要是判断activityInfo是否为空来判断之前Intent是否解析，如果没有解析则需要在这里解析出需要启动的Activity信息，然后调用executeRequest进行实际的启动。
除此之外还记录了一些信息以便重启后可以恢复一些数据。判断是否改变了Configuration，如果需要则通知Configuraion改变，进行Configuraion计算以及通知。
int execute() {
try {
// ...
// 如果activityInfo为空，则说明之前没有解析Intent，就在这里解析，将action等解析为需要启动的Activity信息。
if (mRequest.activityInfo == null) {
mRequest.resolveActivity(mSupervisor);
}
if (mRequest.intent != null) {
String intentAction = mRequest.intent.getAction();
String callingPackage = mRequest.callingPackage;
if (intentAction != null && callingPackage != null
&& (Intent.ACTION_REQUEST_SHUTDOWN.equals(intentAction)
|| Intent.ACTION_SHUTDOWN.equals(intentAction)
|| Intent.ACTION_REBOOT.equals(intentAction))) {
// 记录关机检测点，以便重启后可以恢复一些状态。
ShutdownCheckPoints.recordCheckPoint(intentAction, callingPackage, null);
}
}
int res;
synchronized (mService.mGlobalLock) {
// 检测Configuration是否需要变化
final boolean globalConfigWillChange = mRequest.globalConfig != null
&& mService.getGlobalConfiguration().diff(mRequest.globalConfig) != 0;
final Task rootTask = mRootWindowContainer.getTopDisplayFocusedRootTask();
if (rootTask != null) {
rootTask.mConfigWillChange = globalConfigWillChange;
}
// ...
try {
// 具体启动的逻辑，详见1.7
res = executeRequest(mRequest);
} finally {
mRequest.logMessage.append(" result code=").append(res);
Slog.i(TAG, mRequest.logMessage.toString());
mRequest.logMessage.setLength(0);
}
Binder.restoreCallingIdentity(origId);
if (globalConfigWillChange) {
// ...
// 通知Configuration变化
mService.updateConfigurationLocked(mRequest.globalConfig, null, false);
}
// ... 记录启动消耗时间等信息
// 等待启动结果
if (mRequest.waitResult != null) {
mRequest.waitResult.result = res;
res = waitResultIfNeeded(mRequest.waitResult, mLastStartActivityRecord,
launchingState);
}
return getExternalResult(res);
}
} finally {
onExecutionComplete();
}
} 1.7 executeRequest
这里主要是一些预处理，resultRecord的判定，然后是对Intent中的信息进行解析，解析结果主要是ResolveInfo,里面有一个ActivityInfo。
ResolveInfo里面有用于Intent筛选的信息，如IntentFilter.还有一些图标，labels等信息。
ResolveInfo持有一个ActivityInfo，里面是Activity的一些信息，如launchMode，taskAffinity（acitivity启动的Task），启动activity所需的permission等。
这些信息几乎都是来源于AndroidManifest.xml，所以这里解析其实是通过PackageManagerService，我们这里就不细看了。
此外还有一些特殊场景的处理，如语音会话的启动，启动需要先启动用户确认授权Activity等。
然后就是构建ActivityRecord，这个在WMS章节提过，Activity在system_server侧就是一个ActivityRecord，会在WMS等窗口树上，就是这里创建的。
最后调用了startActivityUnchecked，进一步做启动Activity的操作。
private int executeRequest(Request request) {
// ... 一些局部变量声明
// ...
ActivityRecord sourceRecord = null;
ActivityRecord resultRecord = null;
// 如果requestCode大于0，且SourceRecord没有finish，则说明这次启动activity结束后是需要给resultRecord返回结果的。
if (resultTo != null) {
sourceRecord = ActivityRecord.isInAnyTask(resultTo);
if (sourceRecord != null) {
if (requestCode >= 0 && !sourceRecord.finishing) {
resultRecord = sourceRecord;
}
}
}
final int launchFlags = intent.getFlags();
// FLAG_ACTIVITY_FORWARD_RESULT作用：假如A启动B，B使用FLAG_ACTIVITY_FORWARD_RESULT启动C，则C返回的结果给A。
if ((launchFlags & Intent.FLAG_ACTIVITY_FORWARD_RESULT) != 0 && sourceRecord != null) {
if (requestCode >= 0) {
SafeActivityOptions.abort(options);
return ActivityManager.START_FORWARD_AND_REQUEST_CONFLICT;
}
resultRecord = sourceRecord.resultTo;
if (resultRecord != null && !resultRecord.isInRootTaskLocked()) {
resultRecord = null;
}
resultWho = sourceRecord.resultWho;
requestCode = sourceRecord.requestCode;
sourceRecord.resultTo = null;
if (resultRecord != null) {
resultRecord.removeResultsLocked(sourceRecord, resultWho, requestCode);
}
if (sourceRecord.launchedFromUid == callingUid) {
callingPackage = sourceRecord.launchedFromPackage;
callingFeatureId = sourceRecord.launchedFromFeatureId;
}
}
// 找不到处理Intent的类
if (err == ActivityManager.START_SUCCESS && intent.getComponent() == null) {
err = ActivityManager.START_INTENT_NOT_RESOLVED;
}
// 找不到Intent对应的Activity类
if (err == ActivityManager.START_SUCCESS && aInfo == null) {
err = ActivityManager.START_CLASS_NOT_FOUND;
}
// ... 语音会话启动，需要鉴权，处理兼容性问题
// ... Intent权限检查
if (request.allowPendingRemoteAnimationRegistryLookup) {
checkedOptions = mService.getActivityStartController()
.getPendingRemoteAnimationRegistry()
.overrideOptionsIfNeeded(callingPackage, checkedOptions);
}
if (mService.mController != null) {
try {
Intent watchIntent = intent.cloneFilter();
abort |= !mService.mController.activityStarting(watchIntent,
aInfo.applicationInfo.packageName);
} catch (RemoteException e) {
mService.mController = null;
}
}
mInterceptor.setStates(userId, realCallingPid, realCallingUid, startFlags, callingPackage,
callingFeatureId);
// ...
// 这个ACTION_REVIEW_PERMISSIONS是给用户确认是否授于XXX权限
if (aInfo != null) {
if (mService.getPackageManagerInternalLocked().isPermissionsReviewRequired(
aInfo.packageName, userId)) {
final IIntentSender target = mService.getIntentSenderLocked(
ActivityManager.INTENT_SENDER_ACTIVITY, callingPackage, callingFeatureId,
callingUid, userId, null, null, 0, new Intent[]{intent},
new String[]{resolvedType}, PendingIntent.FLAG_CANCEL_CURRENT
| PendingIntent.FLAG_ONE_SHOT, null);
Intent newIntent = new Intent(Intent.ACTION_REVIEW_PERMISSIONS);
// ...
}
}
// 处理临时应用程序，安装成功或者安装失败提示。
if (rInfo != null && rInfo.auxiliaryInfo != null) {
intent = createLaunchIntent(rInfo.auxiliaryInfo, request.ephemeralIntent,
callingPackage, callingFeatureId, verificationBundle, resolvedType, userId);
resolvedType = null;
callingUid = realCallingUid;
callingPid = realCallingPid;
// The ephemeral installer shouldn't get any permission grants
// intended for the original destination
intentGrants = null;
aInfo = mSupervisor.resolveActivity(intent, rInfo, startFlags, null /*profilerInfo*/);
}
if (callerApp == null && realCallingPid > 0) {
final WindowProcessController wpc = mService.mProcessMap.getProcess(realCallingPid);
if (wpc != null) {
callerApp = wpc;
}
}
// 构建ActivityRecord
final ActivityRecord r = new ActivityRecord.Builder(mService)
.setCaller(callerApp)
.setLaunchedFromPid(callingPid)
.setLaunchedFromUid(callingUid)
.setLaunchedFromPackage(callingPackage)
.setLaunchedFromFeature(callingFeatureId)
.setIntent(intent)
.setResolvedType(resolvedType)
.setActivityInfo(aInfo)
.setConfiguration(mService.getGlobalConfiguration())
.setResultTo(resultRecord)
.setResultWho(resultWho)
.setRequestCode(requestCode)
.setComponentSpecified(request.componentSpecified)
.setRootVoiceInteraction(voiceSession != null)
.setActivityOptions(checkedOptions)
.setSourceRecord(sourceRecord)
.build();
mLastStartActivityRecord = r;
WindowProcessController homeProcess = mService.mHomeProcess;
boolean isHomeProcess = homeProcess != null
&& aInfo.applicationInfo.uid == homeProcess.mUid;
if (balCode != BAL_BLOCK && !isHomeProcess) {
mService.resumeAppSwitches();
}
// 调用startActivityUnchecked，详见1.8
mLastStartActivityResult = startActivityUnchecked(r, sourceRecord, voiceSession,
request.voiceInteractor, startFlags, checkedOptions,
inTask, inTaskFragment, balCode, intentGrants, realCallingUid);
if (request.outActivity != null) {
request.outActivity[0] = mLastStartActivityRecord;
}
return mLastStartActivityResult;
}1.8 startActivityUnchecked
处理启动动画相关的逻辑。调用startActivityInner
private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, ActivityOptions options, Task inTask,
TaskFragment inTaskFragment, @BalCode int balCode,
NeededUriGrants intentGrants, int realCallingUid) {
int result = START_CANCELED;
final Task startedActivityRootTask;
// 创建Activity启动动画的Transaction
final TransitionController transitionController = r.mTransitionController;
Transition newTransition = transitionController.isShellTransitionsEnabled()
? transitionController.createAndStartCollecting(TRANSIT_OPEN) : null;
RemoteTransition remoteTransition = r.takeRemoteTransition();
try {
mService.deferWindowLayout();
transitionController.collect(r);
try {
Trace.traceBegin(Trace.TRACE_TAG_WINDOW_MANAGER, "startActivityInner");
// 详见1.9
result = startActivityInner(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, options, inTask, inTaskFragment, balCode,
intentGrants, realCallingUid);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_WINDOW_MANAGER);
// 处理result，同时会触发启动动画。
startedActivityRootTask = handleStartResult(r, options, result, newTransition,
remoteTransition);
}
} finally {
mService.continueWindowLayout();
}
postStartActivityProcessing(r, result, startedActivityRootTask);
return result;
}1.9 startActivityInner
这里会处理Activity启动的flag等参数，处理新启动的Activity和WMS相关的逻辑（即调整WMS树），具体有以下的操作：
-
选择启动的Activity的DisplayContent
-
判断是否有可以复用的Task，如果没有则新增Task
-
调整Task位置，比如移动到最上层。
-
如果需要，则将ActivityRecord添加到对应的Task上
最后调用resumeFocusedTasksTopActivities，尝试唤醒Focus的Activity。（后面就是Activity声明周期相关的逻辑了）
int startActivityInner(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, ActivityOptions options, Task inTask,
TaskFragment inTaskFragment, @BalCode int balCode,
NeededUriGrants intentGrants, int realCallingUid) {
// 设置初始化状态。主要是计算activity需要启动在哪个屏幕上，如果启动的时候没有指定display，就是这里计算的结果一般是sourceActivity所在的屏幕或者主屏
// 这里计算的diplay不一定是最终的display，如果后续发现有复用Task之类的情况，可能会更新这个display
// 除此之外还有一些option里面的参数处理（如指定了taskId），以及根据Activity launch mode更新launch flag等等。
setInitialState(r, options, inTask, inTaskFragment, startFlags, sourceRecord,
voiceSession, voiceInteractor, balCode, realCallingUid);
// 计算launch flag，会影响到后面是否需要new task或者敷用task等等。
computeLaunchingTaskFlags();
mIntent.setFlags(mLaunchFlags);
// ... // 根据Activity的LaunchMode以及mLaunchFlags等信息，计算是否有可以复用的Task final Task reusedTask = getReusableTask(); // ... // computeTargetTask根据mLaunchFlags和sourceRecord等信息，计算是否已经有存在的Task用来启动目标的Activity // （比如mLaunchFlags有FLAG_ACTIVITY_NEW_TASK，表示要新增Task，computeTargetTask一般就会返回null） final Task targetTask = reusedTask != null ? reusedTask : computeTargetTask(); final boolean newTask = targetTask == null; mTargetTask = targetTask; // 会根据计算出来的targetTask重新计算需要将Activity启动到哪个屏幕 computeLaunchParams(r, sourceRecord, targetTask); // 合法性检查 int startResult = isAllowedToStart(r, newTask, targetTask); if (startResult != START_SUCCESS) { // ... return startResult; } if (targetTask != null) { // 数量检查，由于每个Activity都有Surface，是系统资源，所以要约束app，每个Task有数量限制 if (targetTask.getTreeWeight() > MAX_TASK_WEIGHT_FOR_ADDING_ACTIVITY) { // ... targetTask.removeImmediately("bulky-task"); return START_ABORTED; } // ... } final ActivityRecord targetTaskTop = newTask ? null : targetTask.getTopNonFinishingActivity(); if (targetTaskTop != null) { // 如果Activity的LaunchMode是SingleInstance，检查一下其他的Task有没有这个activity，有就需要销毁 if (LAUNCH_SINGLE_INSTANCE == mLaunchMode && mSourceRecord != null && targetTask == mSourceRecord.getTask()) { final ActivityRecord activity = mRootWindowContainer.findActivity(mIntent, mStartActivity.info, false); if (activity != null && activity.getTask() != targetTask) { activity.destroyIfPossible("Removes redundant singleInstance"); } } // 判断是否需要加入ActivityRecord（可能是复用原来存在的），还会把targetTask放到目标屏幕最上面。 startResult = recycleTask(targetTask, targetTaskTop, reusedTask, intentGrants); if (startResult != START_SUCCESS) { return startResult; } } else { mAddingToTask = true; } if (mTargetRootTask == null) { mTargetRootTask = getOrCreateRootTask(mStartActivity, mLaunchFlags, targetTask, mOptions); } // 如果需要newTask，根据Affiliate新建一个Task if (newTask) { final Task taskToAffiliate = (mLaunchTaskBehind && mSourceRecord != null) ? mSourceRecord.getTask() : null; setNewTask(taskToAffiliate); } else if (mAddingToTask) { // 否则直接将启动activity添加 addOrReparentStartingActivity(targetTask, "adding to task"); } // ... final Task startedTask = mStartActivity.getTask(); // ... mRootWindowContainer.startPowerModeLaunchIfNeeded( false /* forceSend */, mStartActivity); final boolean isTaskSwitch = startedTask != prevTopTask; mTargetRootTask.startActivityLocked(mStartActivity, topRootTask, newTask, isTaskSwitch, mOptions, sourceRecord); if (mDoResume) { final ActivityRecord topTaskActivity = startedTask.topRunningActivityLocked(); if (!mTargetRootTask.isTopActivityFocusable() || (topTaskActivity != null && topTaskActivity.isTaskOverlay() && mStartActivity != topTaskActivity)) { // 如果activity不是focusable，不能设置为focus，但是仍然要设置可见性。 mTargetRootTask.ensureActivitiesVisible(null /* starting */, 0 /* configChanges */, !PRESERVE_WINDOWS); mTargetRootTask.mDisplayContent.executeAppTransition(); } else { // 需要将Task移动到最上面 if (!mAvoidMoveToFront && mTargetRootTask.isTopActivityFocusable() && !mRootWindowContainer.isTopDisplayFocusedRootTask(mTargetRootTask)) { mTargetRootTask.moveToFront("startActivityInner"); } // 这里resume，详见1.10 mRootWindowContainer.resumeFocusedTasksTopActivities( mTargetRootTask, mStartActivity, mOptions, mTransientLaunch); } } mRootWindowContainer.updateUserRootTask(mStartActivity.mUserId, mTargetRootTask); // Update the recent tasks list immediately when the activity starts mSupervisor.mRecentTasks.add(startedTask); mSupervisor.handleNonResizableTaskIfNeeded(startedTask, mPreferredWindowingMode, mPreferredTaskDisplayArea, mTargetRootTask); // ...画中画相关逻辑 return START_SUCCESS;}
1.10 RootWindowContainer.resumeFocusedTasksTopActivities
这里需要resume Activity。最终都会调用需要resume的Activity所在的rootTask的resumeTopActivityUncheckedLocked。
boolean resumeFocusedTasksTopActivities(
Task targetRootTask, ActivityRecord target, ActivityOptions targetOptions,
boolean deferPause) {
// 如果有其他activity还在resume，直接return
if (!mTaskSupervisor.readyToResume()) {
return false;
}
boolean result = false;
// 如果focus的task就是targetRootTask，就调用resumeTopActivityUncheckedLocked
if (targetRootTask != null && (targetRootTask.isTopRootTaskInDisplayArea()
|| getTopDisplayFocusedRootTask() == targetRootTask)) {
// 详见1.11
result = targetRootTask.resumeTopActivityUncheckedLocked(target, targetOptions,
deferPause);
}
// 遍历每个DisplayContent
for (int displayNdx = getChildCount() - 1; displayNdx >= 0; --displayNdx) {
final DisplayContent display = getChildAt(displayNdx);
final boolean curResult = result;
boolean[] resumedOnDisplay = new boolean[1];
// 遍历所有Task
display.forAllRootTasks(rootTask -> {
final ActivityRecord topRunningActivity = rootTask.topRunningActivity();
if (!rootTask.isFocusableAndVisible() || topRunningActivity == null) {
return;
}
if (rootTask == targetRootTask) {
// 如果是targetRootTask
resumedOnDisplay[0] |= curResult;
return;
}
if (topRunningActivity.isState(RESUMED)
&& topRunningActivity == rootTask.getDisplayArea().topRunningActivity()) {
rootTask.executeAppTransition(targetOptions);
} else {
// 这里会对每个Activity进行判断，如果是target则代表需要resume，会调用Activity对应Task的resumeTopActivityUncheckedLocked，详见1.11
// 如果activity需要pause，调用scheduleTransaction通知端侧
resumedOnDisplay[0] |= topRunningActivity.makeActiveIfNeeded(target);
}
});
result |= resumedOnDisplay[0];
// 前面都没有resume成功
if (!resumedOnDisplay[0]) {
final Task focusedRoot = display.getFocusedRootTask();
// 调用focus task的resumeTopActivityUncheckedLocked
if (focusedRoot != null) {
// 详见1.11
result |= focusedRoot.resumeTopActivityUncheckedLocked(target, targetOptions);
} else if (targetRootTask == null) {
// 如果没有focus task，就resume home activity
result |= resumeHomeActivity(null /* prev */, "no-focusable-task",
display.getDefaultTaskDisplayArea());
}
}
}
return result;
}1.11 Task.resumeTopActivityUncheckedLocked
如果是leafTask，直接调用resumeTopActivityInnerLocked，否则递归调用resumeTopActivityUncheckedLocked，遍历子节点，最终会调用可以focus并且有RunningActivity的leafTask的resumeTopActivityInnerLocked。
boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options,
boolean deferPause) {
// 防止重入
if (mInResumeTopActivity) {
return false;
}
boolean someActivityResumed = false;
try {
mInResumeTopActivity = true;
// 如果是leafTask，直接调用Task的resumeTopActivityInnerLocked
if (isLeafTask()) {
if (isFocusableAndVisible()) {
// 详见1.12
someActivityResumed = resumeTopActivityInnerLocked(prev, options, deferPause);
}
} else {
// 否则递归调用resumeTopActivityUncheckedLocked
int idx = mChildren.size() - 1;
while (idx >= 0) {
final Task child = (Task) getChildAt(idx--);
if (!child.isTopActivityFocusable()) {
continue;
}
if (child.getVisibility(null /* starting */)
!= TASK_FRAGMENT_VISIBILITY_VISIBLE) {
if (child.topRunningActivity() == null) {
continue;
}
break;
}
someActivityResumed |= child.resumeTopActivityUncheckedLocked(prev, options,
deferPause);
if (idx >= mChildren.size()) {
idx = mChildren.size() - 1;
}
}
}
final ActivityRecord next = topRunningActivity(true /* focusableOnly */);
if (next == null || !next.canTurnScreenOn()) {
checkReadyForSleep();
}
} finally {
mInResumeTopActivity = false;
}
return someActivityResumed;
}1.12 Task.resumeTopActivityInnerLocked
遍历当前Task的所有的TaskFragment，调用Top且可resume的TaskFragment的resumeTopActivity
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options,
boolean deferPause) {
if (!mAtmService.isBooting() && !mAtmService.isBooted()) {
return false;
}
final ActivityRecord topActivity = topRunningActivity(true /* focusableOnly */);
if (topActivity == null) {
return resumeNextFocusableActivityWhenRootTaskIsEmpty(prev, options);
}
final boolean[] resumed = new boolean[1];
final TaskFragment topFragment = topActivity.getTaskFragment();
// 调用TaskFragment的resumeTopActivity，详见1.13
resumed[0] = topFragment.resumeTopActivity(prev, options, deferPause);
forAllLeafTaskFragments(f -> {
if (topFragment == f) {
return;
}
if (!f.canBeResumed(null /* starting */)) {
return;
}
resumed[0] |= f.resumeTopActivity(prev, options, deferPause);
}, true);
return resumed[0];
}1.13 TaskFragment.resumeTopActivity
首先会检查是否有activity正在pause，如果有就直接返回，等待pause完成再继续操作。
然后需要检查是否需要pause activity，我们知道如果activity A跳转activity B，会先执行A的pause，再resume B，所以这里如果发现之前的activity没有pause，就先执行pause操作。（如果发生了pause操作，就会顺带检查一下ativity B所在的进程是否启动，如果没有启动就会在这里触发启动，并行进行节约时间，关于启动进程的逻辑我们下一个章节再介绍）
如果发现顶部的activity已经pause了（往往是第二次进这个方法，app pause完成后通知systemserver，systemserver重新执行resumeTopActivity），这个时候就可以进行resume操作。
如果要启动的Activity是复用之前已经创建过的，next.attachedToProcess()为true，这时候主要做的事是修改ActivityRecord的状态到RESUMED，更新Activity可见效以及config，然后通知app侧执行对应的声明周期。
而如果没有复用的Activity，这里是刚刚新建的Activity，则会调用startSpecificActivity来启动Activity。
关于通知App更新生命周期LifecycleManager的逻辑我们会单独有一篇文章来介绍。
final boolean resumeTopActivity(ActivityRecord prev, ActivityOptions options,
boolean deferPause) {
ActivityRecord next = topRunningActivity(true /* focusableOnly */);
if (next == null || !next.canResumeByCompat()) {
return false;
}
next.delayedResume = false;
// ...如果没有正在pause的activty，继续流程
final TaskDisplayArea taskDisplayArea = getDisplayArea();
// 如果top activity已经resume，不做什么操作
if (mResumedActivity == next && next.isState(RESUMED)
&& taskDisplayArea.allResumedActivitiesComplete()) {
// 确保topactivity visible
taskDisplayArea.ensureActivitiesVisible(null /* starting */, 0 /* configChanges */,
false /* preserveWindows */, true /* notifyClients */);
// 确保切换已经执行
executeAppTransition(options);
// ...
return false;
}
// 如果topactivity是paused，并且在sleep，那什么都不用做
if (mLastPausedActivity == next && shouldSleepOrShutDownActivities()) {
executeAppTransition(options);
return false;
}
// ...处理多用户情况
// 从mStoppingActivities remove现在要换新的ActivityRecord
mTaskSupervisor.mStoppingActivities.remove(next);
mTaskSupervisor.setLaunchSource(next.info.applicationInfo.uid);
ActivityRecord lastResumed = null;
final Task lastFocusedRootTask = taskDisplayArea.getLastFocusedRootTask();
if (lastFocusedRootTask != null && lastFocusedRootTask != getRootTaskFragment().asTask()) {
lastResumed = lastFocusedRootTask.getTopResumedActivity();
}
boolean pausing = !deferPause && taskDisplayArea.pauseBackTasks(next);
if (mResumedActivity != null) {
// 如果之前的ResumeActivity还没有resume，现在触发pause，详见1.13.1
pausing |= startPausing(mTaskSupervisor.mUserLeaving, false /* uiSleeping */,
next, "resumeTopActivity");
}
// 如果已经触发pause，进这个分支直接return了，要等pausing完了activity，app回调回来才会进行resume
if (pausing) {
if (next.attachedToProcess()) {
// 更新进程信息，例如adj，启动组件可能需要更新adj
next.app.updateProcessInfo(false /* updateServiceConnectionActivities */,
true /* activityChange */, false /* updateOomAdj */,
false /* addPendingTopUid */);
} else if (!next.isProcessRunning()) {
// 如果没有绑定进程。那么就需要新启动进程。
// 这个流程我们下一章再介绍。
final boolean isTop = this == taskDisplayArea.getFocusedRootTask();
mAtmService.startProcessAsync(next, false /* knownToBeDead */, isTop,
isTop ? HostingRecord.HOSTING_TYPE_NEXT_TOP_ACTIVITY
: HostingRecord.HOSTING_TYPE_NEXT_ACTIVITY);
}
if (lastResumed != null) {
lastResumed.setWillCloseOrEnterPip(true);
}
return true;
} else if (mResumedActivity == next && next.isState(RESUMED)
&& taskDisplayArea.allResumedActivitiesComplete()) {
// 确保AppTrasnsition。
executeAppTransition(options);
return true;
}
// ...
// ... 处理动画
mTaskSupervisor.mNoAnimActivities.clear();
// 如果需要启动ActivityRecord的app已经绑定进程，这里需要做resume操作了
// 如果activity没有复用，是新启动的这里一般是false。
if (next.attachedToProcess()) {
// mLastPausedActivity
final boolean lastActivityTranslucent = inMultiWindowMode()
|| mLastPausedActivity != null && !mLastPausedActivity.occludesParent();
// 设置Activity可见性
if (!next.isVisibleRequested() || next.mAppStopped || lastActivityTranslucent) {
next.app.addToPendingTop();
next.setVisibility(true);
}
// 收集app启动速度
next.startLaunchTickingLocked();
ActivityRecord lastResumedActivity =
lastFocusedRootTask == null ? null
: lastFocusedRootTask.getTopResumedActivity();
final ActivityRecord.State lastState = next.getState();
mAtmService.updateCpuStats();
// 设置activity状态resume
next.setState(RESUMED, "resumeTopActivity");
boolean notUpdated = true;
if (shouldBeVisible(next)) {
// 更新activity visible以及配置
notUpdated = !mRootWindowContainer.ensureVisibilityAndConfig(next, getDisplayId(),
true /* markFrozenIfConfigChanged */, false /* deferResume */);
}
if (notUpdated) {
ActivityRecord nextNext = topRunningActivity();
if (nextNext != next) {
mTaskSupervisor.scheduleResumeTopActivities();
}
if (!next.isVisibleRequested() || next.mAppStopped) {
next.setVisibility(true);
}
next.completeResumeLocked();
return true;
}
try {
// 回调app侧，通知app activity需要到resume状态。
final ClientTransaction transaction =
ClientTransaction.obtain(next.app.getThread(), next.token);
// ...
transaction.setLifecycleStateRequest(
ResumeActivityItem.obtain(next.app.getReportedProcState(),
dc.isNextTransitionForward(), next.shouldSendCompatFakeFocus()));
mAtmService.getLifecycleManager().scheduleTransaction(transaction);
} catch (Exception e) {
// Whoops, need to restart this activity!
ProtoLog.v(WM_DEBUG_STATES, "Resume failed; resetting state to %s: "
+ "%s", lastState, next);
next.setState(lastState, "resumeTopActivityInnerLocked");
// lastResumedActivity being non-null implies there is a lastStack present.
if (lastResumedActivity != null) {
lastResumedActivity.setState(RESUMED, "resumeTopActivityInnerLocked");
}
Slog.i(TAG, "Restarting because process died: " + next);
if (!next.hasBeenLaunched) {
next.hasBeenLaunched = true;
} else if (SHOW_APP_STARTING_PREVIEW && lastFocusedRootTask != null
&& lastFocusedRootTask.isTopRootTaskInDisplayArea()) {
next.showStartingWindow(false /* taskSwitch */);
}
mTaskSupervisor.startSpecificActivity(next, true, false);
return true;
}
try {
next.completeResumeLocked();
} catch (Exception e) {
// If any exception gets thrown, toss away this
// activity and try the next one.
Slog.w(TAG, "Exception thrown during resume of " + next, e);
next.finishIfPossible("resume-exception", true /* oomAdj */);
return true;
}
} else {
if (!next.hasBeenLaunched) {
next.hasBeenLaunched = true;
} else {
if (SHOW_APP_STARTING_PREVIEW) {
next.showStartingWindow(false /* taskSwich */);
}
}
// 正常新启动Activity而不是复用会走这里，详见1.14
mTaskSupervisor.startSpecificActivity(next, true, true);
}
return true;
}1.13.1 TaskFragment.startPausing
更新需要pause的ActivityRecord状态到PAUSING，通知app侧进行对应的生命周期操作。
如果pause到Activity对应的进程已经不在了，就直接调用resumeFocusedTasksTopActivities继续唤醒topActivity的流程。
否则等待app pause流程完成后，app会回调system_server,最终也会走到completePause，里面会将ActivityRecord状态改为PAUSED，并且重新调用resumeFocusedTasksTopActivities。（关于通知app的生命周期以及app回调流程，我们会单独有一篇文章来介绍）
boolean startPausing(boolean userLeaving, boolean uiSleeping, ActivityRecord resuming,
String reason) {
// ...
// ... 合理性检查，如正在暂停的activity不能是我们正在唤醒的activity resuming
ProtoLog.v(WM_DEBUG_STATES, "Moving to PAUSING: %s", prev);
mPausingActivity = prev;
mLastPausedActivity = prev;
if (!prev.finishing && prev.isNoHistory()
&& !mTaskSupervisor.mNoHistoryActivities.contains(prev)) {
mTaskSupervisor.mNoHistoryActivities.add(prev);
}
// 修改状态为PAUSING
prev.setState(PAUSING, "startPausingLocked");
prev.getTask().touchActiveTime();
mAtmService.updateCpuStats();
boolean pauseImmediately = false;
boolean shouldAutoPip = false;
if (resuming != null) {
// ...画中画相关逻辑
}
if (prev.attachedToProcess()) {
if (shouldAutoPip) {
prev.mPauseSchedulePendingForPip = true;
boolean didAutoPip = mAtmService.enterPictureInPictureMode(
prev, prev.pictureInPictureArgs, false /* fromClient */);
} else {
// 通过getLifecycleManager().scheduleTransaction通知app进行pause到生命周期
schedulePauseActivity(prev, userLeaving, pauseImmediately,
false /* autoEnteringPip */, reason);
}
} else {
mPausingActivity = null;
mLastPausedActivity = null;
mTaskSupervisor.mNoHistoryActivities.remove(prev);
}
// ...
// If already entered PIP mode, no need to keep pausing.
if (mPausingActivity != null) {
// ...
if (pauseImmediately) {
// 如果需要立刻完成pause，不等待app侧完成pause再进行回调，这里直接执行completePause继续唤醒流程
// completePause会将ActivityRecord状态改为PAUSED，并且重新调用resumeFocusedTasksTopActivities，
completePause(false, resuming);
return false;
} else {
prev.schedulePauseTimeout();
if (!uiSleeping) {
mTransitionController.setReady(this, false /* ready */);
}
return true;
}
} else {
// ... 直接调用resumeFocusedTasksTopActivities继续唤醒流程
if (resuming == null) {
mRootWindowContainer.resumeFocusedTasksTopActivities();
}
return false;
}
}1.14 ActivityTaskSupervisor.startSpecificActivity
如果app进程已经启动，则会调用realStartActivityLocked进行Activity的启动，否则会调用startProcessAsync启动对应进程，启动进程的流程我们下一篇文章再介绍。
void startSpecificActivity(ActivityRecord r, boolean andResume, boolean checkConfig) {
final WindowProcessController wpc =
mService.getProcessController(r.processName, r.info.applicationInfo.uid);
boolean knownToBeDead = false;
// 如果app进程已经启动，则会调用realStartActivityLocked来启动activity，详见1.15
if (wpc != null && wpc.hasThread()) {
// ...
realStartActivityLocked(r, wpc, andResume, checkConfig);
return;
// ...
}
// ...
final boolean isTop = andResume && r.isTopRunningActivity();
// 否则会触发启动进程的流程。
mService.startProcessAsync(r, knownToBeDead, isTop,
isTop ? HostingRecord.HOSTING_TYPE_TOP_ACTIVITY
: HostingRecord.HOSTING_TYPE_ACTIVITY);
}1.15 ActivityTaskSupervisor.realStartActivityLocked
主要通过getLifecycleManager通知app启动activity。最后还会调用rootTask.minimalResumeActivityLocked来设置Activity的可见性。
boolean realStartActivityLocked(ActivityRecord r, WindowProcessController proc,
boolean andResume, boolean checkConfig) throws RemoteException {
// ...检测所有Activity pause完成
final Task task = r.getTask();
final Task rootTask = task.getRootTask();
try {
r.startFreezingScreenLocked(proc, 0);
// schedule launch ticks to collect information about slow apps.
r.startLaunchTickingLocked();
r.lastLaunchTime = SystemClock.uptimeMillis();
r.setProcess(proc);
if (andResume && !r.canResumeByCompat()) {
andResume = false;
}
r.notifyUnknownVisibilityLaunchedForKeyguardTransition();
// ...
if (checkConfig) {
// 更新Activity visible以及configuration
mRootWindowContainer.ensureVisibilityAndConfig(r, r.getDisplayId(),
false /* markFrozenIfConfigChanged */, true /* deferResume */);
}
// ...
try {
// ...
// 通知app侧创建启动activity。
final ClientTransaction clientTransaction = ClientTransaction.obtain(
proc.getThread(), r.token);
final boolean isTransitionForward = r.isTransitionForward();
final IBinder fragmentToken = r.getTaskFragment().getFragmentToken();
final int deviceId = getDeviceIdForDisplayId(r.getDisplayId());
clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),
System.identityHashCode(r), r.info,
mergedConfiguration.getGlobalConfiguration(),
mergedConfiguration.getOverrideConfiguration(), deviceId,
r.getFilteredReferrer(r.launchedFromPackage), task.voiceInteractor,
proc.getReportedProcState(), r.getSavedState(), r.getPersistentSavedState(),
results, newIntents, r.takeOptions(), isTransitionForward,
proc.createProfilerInfoIfNeeded(), r.assistToken, activityClientController,
r.shareableActivityToken, r.getLaunchedFromBubble(), fragmentToken));
final ActivityLifecycleItem lifecycleItem;
if (andResume) {
lifecycleItem = ResumeActivityItem.obtain(isTransitionForward,
r.shouldSendCompatFakeFocus());
} else {
lifecycleItem = PauseActivityItem.obtain();
}
clientTransaction.setLifecycleStateRequest(lifecycleItem);
mService.getLifecycleManager().scheduleTransaction(clientTransaction);
// ...
}
// ...
if (andResume && readyToResume()) {
// 详见1.16
rootTask.minimalResumeActivityLocked(r);
}
}1.16 Task.minimalResumeActivityLocked
void minimalResumeActivityLocked(ActivityRecord r) {
ProtoLog.v(WM_DEBUG_STATES, "Moving to RESUMED: %s (starting new instance) "
+ "callers=%s", r, Debug.getCallers(5));
r.setState(RESUMED, "minimalResumeActivityLocked");
// 详见1.17
r.completeResumeLocked();
}1.17 ActivityRecord.completeResumeLocked
这个方法其实只要resume了Activity的路径都会走到。
我们的主要关注更新可见性相关逻辑，其余的逻辑就忽略了。我们知道Activity可见状态是resume的时候，所以在这里会更新可见性。
通过setVisibility设置ActivityRecord可见，然后调用reportResumedActivityLocked。
void completeResumeLocked() {
final boolean wasVisible = mVisibleRequested;
setVisibility(true);
// ...
// 详见1.18
mTaskSupervisor.reportResumedActivityLocked(this);
// ...
}1.18 ActivityTaskSupervisor.reportResumedActivityLocked
boolean reportResumedActivityLocked(ActivityRecord r) {
// resumed的Activity不能在StoppingActivities集合里
mStoppingActivities.remove(r);
final Task rootTask = r.getRootTask();
if (rootTask.getDisplayArea().allResumedActivitiesComplete()) {
// 这个方法用来更新Activity的可见性，详见1.19
mRootWindowContainer.ensureActivitiesVisible(null, 0, !PRESERVE_WINDOWS);
mRootWindowContainer.executeAppTransitionForAllDisplay();
return true;
}
return false;
}1.19 Task.ensureActivitiesVisible
RootWindowContainer.ensureActivitiesVisible会递归遍历DisplayContent,调用DisplayContent.ensureActivitiesVisible
同样DisplayContent会调用RootTask的ensureActivitiesVisible
我们直接看Task.ensureActivitiesVisible
遍历LeafTask，调用updateActivityVisibilities方法。
void ensureActivitiesVisible(@Nullable ActivityRecord starting, int configChanges,
boolean preserveWindows, boolean notifyClients) {
mTaskSupervisor.beginActivityVisibilityUpdate();
try {
forAllLeafTasks(task -> {
// 详见1.20
task.updateActivityVisibilities(starting, configChanges, preserveWindows,
notifyClients);
}, true /* traverseTopToBottom */);
if (mTranslucentActivityWaiting != null &&
mUndrawnActivitiesBelowTopTranslucent.isEmpty()) {
notifyActivityDrawnLocked(null);
}
} finally {
mTaskSupervisor.endActivityVisibilityUpdate();
}
}1.20 TaskFragment.updateActivityVisibilities
只是调用了mEnsureActivitiesVisibleHelper.process
final void updateActivityVisibilities(@Nullable ActivityRecord starting, int configChanges,
boolean preserveWindows, boolean notifyClients) {
mTaskSupervisor.beginActivityVisibilityUpdate();
try {
// 详见1.21
mEnsureActivitiesVisibleHelper.process(
starting, configChanges, preserveWindows, notifyClients);
} finally {
mTaskSupervisor.endActivityVisibilityUpdate();
}
}1.21 EnsureActivitiesVisibleHelper.process
递归遍历所有TaskFragment.updateActivityVisibilities，如果TaskFragment有activity，则更新activity可见性状态。
void process(@Nullable ActivityRecord starting, int configChanges, boolean preserveWindows,
boolean notifyClients) {
reset(starting, configChanges, preserveWindows, notifyClients);
if (mTopRunningActivity != null && mTaskFragment.asTask() != null) {
// TODO(14709632): Check if this needed to be implemented in TaskFragment.
mTaskFragment.asTask().checkTranslucentActivityWaiting(mTopRunningActivity);
}
// 判断一些不应resumeActivity的情况。
// 我们不应该恢复在后面启动的Activity，因为这些活动实际上在其他全屏的Activity后面，但仍然需要可见（例如执行Recents动画）。
final boolean resumeTopActivity = mTopRunningActivity != null
&& !mTopRunningActivity.mLaunchTaskBehind
&& mTaskFragment.canBeResumed(starting)
&& (starting == null || !starting.isDescendantOf(mTaskFragment));
ArrayList<TaskFragment> adjacentTaskFragments = null;
for (int i = mTaskFragment.mChildren.size() - 1; i >= 0; --i) {
final WindowContainer child = mTaskFragment.mChildren.get(i);
final TaskFragment childTaskFragment = child.asTaskFragment();
if (childTaskFragment != null
&& childTaskFragment.getTopNonFinishingActivity() != null) {
// 递归遍历调用子TaskFragment.updateActivityVisibilities
childTaskFragment.updateActivityVisibilities(starting, configChanges,
preserveWindows, notifyClients);
// 判断当前Task边界是否和父Task边界相同，如果相同，且不透明，则他完全遮盖了下面的兄弟Task
mBehindFullyOccludedContainer |=
(childTaskFragment.getBounds().equals(mTaskFragment.getBounds())
&& !childTaskFragment.isTranslucent(starting));
if (mAboveTop && mTopRunningActivity.getTaskFragment() == childTaskFragment) {
mAboveTop = false;
}
// 如果之前的Task已经全部遮盖了，就直接continue
if (mBehindFullyOccludedContainer) {
continue;
}
if (adjacentTaskFragments != null && adjacentTaskFragments.contains(
childTaskFragment)) {
if (!childTaskFragment.isTranslucent(starting)
&& !childTaskFragment.getAdjacentTaskFragment().isTranslucent(
starting)) {
// Everything behind two adjacent TaskFragments are occluded.
mBehindFullyOccludedContainer = true;
}
continue;
}
final TaskFragment adjacentTaskFrag = childTaskFragment.getAdjacentTaskFragment();
if (adjacentTaskFrag != null) {
if (adjacentTaskFragments == null) {
adjacentTaskFragments = new ArrayList<>();
}
adjacentTaskFragments.add(adjacentTaskFrag);
}
} else if (child.asActivityRecord() != null) {
// 设置activity visible state，详见1.22
setActivityVisibilityState(child.asActivityRecord(), starting, resumeTopActivity);
}
}
}1.22 EnsureActivitiesVisibleHelper.setActivityVisibilityState
判断activity是否可见，如果是可见的，则需要设置他的可见状态。
针对不同情况有不同的处理，如果可见的activity还没有attachedToProcess，则调用makeVisibleAndRestartIfNeeded，会设置Activity可见，且如果正在starting的Activity不是当前正在设置可见的Activity，还会重新调用startSpecificActivity来启动Activity。
而其他情况则调用makeActiveIfNeeded或者makeVisibleIfNeeded设置Activity可见，makeVisibleIfNeeded最终也会调用到makeActiveIfNeeded，而makeActiveIfNeeded我们前面已经介绍过了。1.10里也调用这个方法。会重新走上面的流程，而在1.13里如果Activity已经创建过，则会走另一个分支，直接设置Activity可见，通知app侧activity resume的生命周期。
private void setActivityVisibilityState(ActivityRecord r, ActivityRecord starting,
final boolean resumeTopActivity) {
final boolean isTop = r == mTopRunningActivity;
if (mAboveTop && !isTop) {
// 如果不是最上层的activity，设置不可见
r.makeInvisible();
return;
}
mAboveTop = false;
r.updateVisibilityIgnoringKeyguard(mBehindFullyOccludedContainer);
// 计算Activity是否可见
final boolean reallyVisible = r.shouldBeVisibleUnchecked();
// Check whether activity should be visible without Keyguard influence
if (r.visibleIgnoringKeyguard) {
if (r.occludesParent()) {
mBehindFullyOccludedContainer = true;
} else {
mBehindFullyOccludedContainer = false;
}
} else if (r.isState(INITIALIZING)) {
r.cancelInitializing();
}
if (reallyVisible) {
if (r.finishing) {
return;
}
if (r != mStarting && mNotifyClients) {
r.ensureActivityConfiguration(0 /* globalChanges */, mPreserveWindows,
true /* ignoreVisibility */);
}
// 如果ActivityRecord还没有attch到进程上
if (!r.attachedToProcess()) {
// 设置activity visible
// 且如果当前需要设置可见的activity不是正在starting的activity，就会调用startSpecificActivity去启动当前设置可见的activity
makeVisibleAndRestartIfNeeded(mStarting, mConfigChanges,
resumeTopActivity && isTop, r);
} else if (r.isVisibleRequested()) {
if (r.mClientVisibilityDeferred && mNotifyClients) {
// 这个方法之前提过，在1.10的方法中也调用了该方法。
// 如果需要走会resumeTopActivity的流程，相当于重新走了上面的流程，只是如果activity已经构建，在1.13中，会走另一条分支，直接通知app侧resume activity，同时会通知client。而不是走startSpecificActivity流程了。
r.makeActiveIfNeeded(r.mClientVisibilityDeferred ? null : starting);
r.mClientVisibilityDeferred = false;
}
r.handleAlreadyVisible();
if (mNotifyClients) {
r.makeActiveIfNeeded(mStarting);
}
} else {
// mNotifyClients为true，则也会调用到makeActiveIfNeeded，否则设置mClientVisibilityDeferred为true，推迟操作。
r.makeVisibleIfNeeded(mStarting, mNotifyClients);
}
// Aggregate current change flags.
mConfigChanges |= r.configChangeFlags;
} else {
// 否者设置不可见
r.makeInvisible();
}
if (!mBehindFullyOccludedContainer && mTaskFragment.isActivityTypeHome()
&& r.isRootOfTask()) {
mBehindFullyOccludedContainer = true;
}
}小结
Activity的启动流程非常长，核心思想主要是两个，一个是处理WMS的窗口层次结构，在WMS树上加上新增的ActivityRecord（如需要可能还有Task），或者是找到复用的ActivityRecord；另一个则是需要处理AMS侧activity生命周期以及可见性相关的逻辑。
一个未启动的应用首次创建Activity是会走启动进程流程的，与当前的逻辑略有不同，我们下一篇文章来介绍。
还有app侧对生命周期的控制，我们在下下篇文章中介绍。