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调用链 SystemServer.startOtherServices() -> ActivityManagerService.systemReady() -> ActivityTaskManagerService.startHomeOnAllDisplays() -> RootWindowContainer.startHomeOnTaskDisplayArea() -> ActivityStartController.startHomeActivity()
ActivityTaskManagerService.startHomeOnAllDisplays(currentUserId, "systemReady");
public boolean startHomeOnAllDisplays(int userId, String reason) {
synchronized (mGlobalLock) {
return mRootWindowContainer.startHomeOnAllDisplays(userId, reason);
}
}
ActivityStartController.startHomeActivity
void startHomeActivity(Intent intent, ActivityInfo aInfo, String reason,
TaskDisplayArea taskDisplayArea) {
final ActivityOptions options = ActivityOptions.makeBasic();
options.setLaunchWindowingMode(WINDOWING_MODE_FULLSCREEN);
if (!ActivityRecord.isResolverActivity(aInfo.name)) {
// The resolver activity shouldn't be put in root home task because when the
// foreground is standard type activity, the resolver activity should be put on the
// top of current foreground instead of bring root home task to front.
options.setLaunchActivityType(ACTIVITY_TYPE_HOME);
}
final int displayId = taskDisplayArea.getDisplayId();
options.setLaunchDisplayId(displayId);
options.setLaunchTaskDisplayArea(taskDisplayArea.mRemoteToken
.toWindowContainerToken());
// The home activity will be started later, defer resuming to avoid unnecessary operations
// (e.g. start home recursively) when creating root home task.
mSupervisor.beginDeferResume();
final Task rootHomeTask;
try {
// Make sure root home task exists on display area.
rootHomeTask = taskDisplayArea.getOrCreateRootHomeTask(ON_TOP);
} finally {
mSupervisor.endDeferResume();
}
//通过ActivityStarter执行启动
mLastHomeActivityStartResult = obtainStarter(intent, "startHomeActivity: " + reason)
.setOutActivity(tmpOutRecord)
.setCallingUid(0)
.setActivityInfo(aInfo)
.setActivityOptions(options.toBundle())
.execute();
mLastHomeActivityStartRecord = tmpOutRecord[0];
if (rootHomeTask.mInResumeTopActivity) {
// If we are in resume section already, home activity will be initialized, but not
// resumed (to avoid recursive resume) and will stay that way until something pokes it
// again. We need to schedule another resume.
mSupervisor.scheduleResumeTopActivities();
}
}
ActivityStarter.execute() ->ActivityStarter.executeRequest()
private int executeRequest(Request request) {
if (TextUtils.isEmpty(request.reason)) {
throw new IllegalArgumentException("Need to specify a reason.");
}
mLastStartReason = request.reason;
mLastStartActivityTimeMs = System.currentTimeMillis();
mLastStartActivityRecord = null;
final IApplicationThread caller = request.caller;
Intent intent = request.intent;
NeededUriGrants intentGrants = request.intentGrants;
String resolvedType = request.resolvedType;
ActivityInfo aInfo = request.activityInfo;
ResolveInfo rInfo = request.resolveInfo;
final IVoiceInteractionSession voiceSession = request.voiceSession;
final IBinder resultTo = request.resultTo;
String resultWho = request.resultWho;
int requestCode = request.requestCode;
int callingPid = request.callingPid;
int callingUid = request.callingUid;
String callingPackage = request.callingPackage;
String callingFeatureId = request.callingFeatureId;
final int realCallingPid = request.realCallingPid;
final int realCallingUid = request.realCallingUid;
final int startFlags = request.startFlags;
final SafeActivityOptions options = request.activityOptions;
Task inTask = request.inTask;
int err = ActivityManager.START_SUCCESS;
// Pull the optional Ephemeral Installer-only bundle out of the options early.
final Bundle verificationBundle =
options != null ? options.popAppVerificationBundle() : null;
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;
}
}
final int userId = aInfo != null && aInfo.applicationInfo != null
? UserHandle.getUserId(aInfo.applicationInfo.uid) : 0;
if (err == ActivityManager.START_SUCCESS) {
Slog.i(TAG, "START u" + userId + " {" + intent.toShortString(true, true, true, false)
+ "} from uid " + callingUid);
}
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;
}
}
}
final int launchFlags = intent.getFlags();
if ((launchFlags & Intent.FLAG_ACTIVITY_FORWARD_RESULT) != 0 && sourceRecord != null) {
// Transfer the result target from the source activity to the new one being started,
// including any failures.
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) {
// The new activity is being launched from the same uid as the previous activity
// in the flow, and asking to forward its result back to the previous. In this
// case the activity is serving as a trampoline between the two, so we also want
// to update its launchedFromPackage to be the same as the previous activity.
// Note that this is safe, since we know these two packages come from the same
// uid; the caller could just as well have supplied that same package name itself
// . This specifially deals with the case of an intent picker/chooser being
// launched in the app flow to redirect to an activity picked by the user, where
// we want the final activity to consider it to have been launched by the
// previous app activity.
callingPackage = sourceRecord.launchedFromPackage;
callingFeatureId = sourceRecord.launchedFromFeatureId;
}
}
if (err == ActivityManager.START_SUCCESS && intent.getComponent() == null) {
// We couldn't find a class that can handle the given Intent.
// That's the end of that!
err = ActivityManager.START_INTENT_NOT_RESOLVED;
}
if (err == ActivityManager.START_SUCCESS && aInfo == null) {
// We couldn't find the specific class specified in the Intent.
// Also the end of the line.
err = ActivityManager.START_CLASS_NOT_FOUND;
}
if (err == ActivityManager.START_SUCCESS && sourceRecord != null
&& sourceRecord.getTask().voiceSession != null) {
// If this activity is being launched as part of a voice session, we need to ensure
// that it is safe to do so. If the upcoming activity will also be part of the voice
// session, we can only launch it if it has explicitly said it supports the VOICE
// category, or it is a part of the calling app.
if ((launchFlags & FLAG_ACTIVITY_NEW_TASK) == 0
&& sourceRecord.info.applicationInfo.uid != aInfo.applicationInfo.uid) {
try {
intent.addCategory(Intent.CATEGORY_VOICE);
if (!mService.getPackageManager().activitySupportsIntent(
intent.getComponent(), intent, resolvedType)) {
Slog.w(TAG, "Activity being started in current voice task does not support "
+ "voice: " + intent);
err = ActivityManager.START_NOT_VOICE_COMPATIBLE;
}
} catch (RemoteException e) {
Slog.w(TAG, "Failure checking voice capabilities", e);
err = ActivityManager.START_NOT_VOICE_COMPATIBLE;
}
}
}
if (err == ActivityManager.START_SUCCESS && voiceSession != null) {
// If the caller is starting a new voice session, just make sure the target
// is actually allowing it to run this way.
try {
if (!mService.getPackageManager().activitySupportsIntent(intent.getComponent(),
intent, resolvedType)) {
Slog.w(TAG,
"Activity being started in new voice task does not support: " + intent);
err = ActivityManager.START_NOT_VOICE_COMPATIBLE;
}
} catch (RemoteException e) {
Slog.w(TAG, "Failure checking voice capabilities", e);
err = ActivityManager.START_NOT_VOICE_COMPATIBLE;
}
}
final Task resultRootTask = resultRecord == null
? null : resultRecord.getRootTask();
if (err != START_SUCCESS) {
if (resultRecord != null) {
resultRecord.sendResult(INVALID_UID, resultWho, requestCode, RESULT_CANCELED,
null /* data */, null /* dataGrants */);
}
SafeActivityOptions.abort(options);
return err;
}
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);
boolean restrictedBgActivity = false;
if (!abort) {
try {
Trace.traceBegin(Trace.TRACE_TAG_WINDOW_MANAGER,
"shouldAbortBackgroundActivityStart");
restrictedBgActivity = shouldAbortBackgroundActivityStart(callingUid,
callingPid, callingPackage, realCallingUid, realCallingPid, callerApp,
request.originatingPendingIntent, request.allowBackgroundActivityStart,
intent);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_WINDOW_MANAGER);
}
}
// Merge the two options bundles, while realCallerOptions takes precedence.
ActivityOptions checkedOptions = options != null
? options.getOptions(intent, aInfo, callerApp, mSupervisor) : null;
if (request.allowPendingRemoteAnimationRegistryLookup) {
checkedOptions = mService.getActivityStartController()
.getPendingRemoteAnimationRegistry()
.overrideOptionsIfNeeded(callingPackage, checkedOptions);
}
if (mService.mController != null) {
try {
// The Intent we give to the watcher has the extra data stripped off, since it
// can contain private information.
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);
if (mInterceptor.intercept(intent, rInfo, aInfo, resolvedType, inTask, callingPid,
callingUid, checkedOptions)) {
// activity start was intercepted, e.g. because the target user is currently in quiet
// mode (turn off work) or the target application is suspended
intent = mInterceptor.mIntent;
rInfo = mInterceptor.mRInfo;
aInfo = mInterceptor.mAInfo;
resolvedType = mInterceptor.mResolvedType;
inTask = mInterceptor.mInTask;
callingPid = mInterceptor.mCallingPid;
callingUid = mInterceptor.mCallingUid;
checkedOptions = mInterceptor.mActivityOptions;
// The interception target shouldn't get any permission grants
// intended for the original destination
intentGrants = null;
}
if (abort) {
if (resultRecord != null) {
resultRecord.sendResult(INVALID_UID, resultWho, requestCode, RESULT_CANCELED,
null /* data */, null /* dataGrants */);
}
// We pretend to the caller that it was really started, but they will just get a
// cancel result.
ActivityOptions.abort(checkedOptions);
return START_ABORTED;
}
// If permissions need a review before any of the app components can run, we
// launch the review activity and pass a pending intent to start the activity
// we are to launching now after the review is completed.
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);
int flags = intent.getFlags();
flags |= Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS;
/*
* Prevent reuse of review activity: Each app needs their own review activity. By
* default activities launched with NEW_TASK or NEW_DOCUMENT try to reuse activities
* with the same launch parameters (extras are ignored). Hence to avoid possible
* reuse force a new activity via the MULTIPLE_TASK flag.
*
* Activities that are not launched with NEW_TASK or NEW_DOCUMENT are not re-used,
* hence no need to add the flag in this case.
*/
if ((flags & (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_NEW_DOCUMENT)) != 0) {
flags |= Intent.FLAG_ACTIVITY_MULTIPLE_TASK;
}
newIntent.setFlags(flags);
newIntent.putExtra(Intent.EXTRA_PACKAGE_NAME, aInfo.packageName);
newIntent.putExtra(Intent.EXTRA_INTENT, new IntentSender(target));
if (resultRecord != null) {
newIntent.putExtra(Intent.EXTRA_RESULT_NEEDED, true);
}
intent = newIntent;
// The permissions review target shouldn't get any permission
// grants intended for the original destination
intentGrants = null;
resolvedType = null;
callingUid = realCallingUid;
callingPid = realCallingPid;
rInfo = mSupervisor.resolveIntent(intent, resolvedType, userId, 0,
computeResolveFilterUid(
callingUid, realCallingUid, request.filterCallingUid));
aInfo = mSupervisor.resolveActivity(intent, rInfo, startFlags,
null /*profilerInfo*/);
if (DEBUG_PERMISSIONS_REVIEW) {
final Task focusedRootTask =
mRootWindowContainer.getTopDisplayFocusedRootTask();
Slog.i(TAG, "START u" + userId + " {" + intent.toShortString(true, true,
true, false) + "} from uid " + callingUid + " on display "
+ (focusedRootTask == null ? DEFAULT_DISPLAY
: focusedRootTask.getDisplayId()));
}
}
}
// If we have an ephemeral app, abort the process of launching the resolved intent.
// Instead, launch the ephemeral installer. Once the installer is finished, it
// starts either the intent we resolved here [on install error] or the ephemeral
// app [on install success].
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*/);
}
// TODO (b/187680964) Correcting the caller/pid/uid when start activity from shortcut
// Pending intent launched from systemui also depends on caller app
if (callerApp == null && realCallingPid > 0) {
final WindowProcessController wpc = mService.mProcessMap.getProcess(realCallingPid);
if (wpc != null) {
callerApp = wpc;
}
}
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;
if (r.appTimeTracker == null && sourceRecord != null) {
// If the caller didn't specify an explicit time tracker, we want to continue
// tracking under any it has.
r.appTimeTracker = sourceRecord.appTimeTracker;
}
// Only allow app switching to be resumed if activity is not a restricted background
// activity and target app is not home process, otherwise any background activity
// started in background task can stop home button protection mode.
// As the targeted app is not a home process and we don't need to wait for the 2nd
// activity to be started to resume app switching, we can just enable app switching
// directly.
WindowProcessController homeProcess = mService.mHomeProcess;
boolean isHomeProcess = homeProcess != null
&& aInfo.applicationInfo.uid == homeProcess.mUid;
if (!restrictedBgActivity && !isHomeProcess) {
mService.resumeAppSwitches();
}
mLastStartActivityResult = startActivityUnchecked(r, sourceRecord, voiceSession,
request.voiceInteractor, startFlags, true /* doResume */, checkedOptions, inTask,
restrictedBgActivity, intentGrants);
if (request.outActivity != null) {
request.outActivity[0] = mLastStartActivityRecord;
}
return mLastStartActivityResult;
}
阶段一：ActivityStarter 的任务栈裁决
ActivityStarter 会执行 executeRequest(...) 方法，根据启动标志（Intent Flag）和 Activity 类型，决定如何安放这个新的 Activity。
对于 Home Activity，系统会执行特殊的 HOME 任务栈处理逻辑：
- 查找或复用 Home 任务：在
RootWindowContainer中，系统会找到我们在startHomeActivity()中确保存在的rootHomeTask（即根 Home 任务）。如果发现该任务栈已经存在一个 Launcher 实例，系统会决定是复用它还是重置它，而不是重复创建。 - 清除栈顶干扰：如果当前 Home 任务栈的栈顶有其他的临时 Activity（比如弹窗或第三方应用页面被意外压入），系统会调用
Task.deliverClearTop或Task.performClearTask将其清除，确保桌面位于该任务栈的栈顶。 - 生成 ActivityRecord：系统为即将启动的桌面 Activity 创建一个
ActivityRecord对象，该对象记录了桌面 Activity 的所有状态信息，并将其挂载到rootHomeTask的任务栈中。
阶段二：从 System 进程到 App 进程的生命周期调度
任务栈安置完毕后，系统需要真正地“运行”桌面应用的代码。这一步涉及进程间通信（IPC），由 ActivityTaskManagerService 和 ApplicationThread 协作完成：
-
获取或创建应用进程：
ActivityStarter会调用ActivityManagerService.startProcessAsync，检查桌面应用的进程是否存在。如果未启动（如开机首次启动），系统会通过 Zygote 进程孵化（Fork） 出桌面应用的主进程。 -
绑定 Application：进程创建后，系统会调用桌面应用的
Application.onCreate()，完成应用上下文和资源的初始化。 -
事务调度：系统通过
ClientLifecycleManager向桌面应用进程发送事务（Transaction）。对于桌面启动，通常是按顺序发送：ON_CREATE事务（对应onCreate）ON_START事务（对应onStart）ON_RESUME事务（对应onResume）
-
处理系统窗口：在
onResume阶段，系统还会调用Activity.makeVisible()，为后续的窗口显示做最后准备。
阶段三：窗口绘制与最终显示
当桌面应用的 onResume 执行完毕，Activity 进入 RESUMED 状态，但此时用户可能还看不到界面，因为窗口（Window）尚未完成第一次绘制（即"冷启动"） ：
- 添加窗口：桌面应用通过
ViewManager.addView（实际上是WindowManagerGlobal）将根布局（DecorView）添加到WindowManager中。这会触发Session.addToDisplay的跨进程调用，通知 System UI 进程（或系统服务）创建一个WindowState。 - 申请 Surface：系统服务端的
WindowState会向SurfaceFlinger申请一块用于显示的 Surface 缓冲区域。 - 测量、布局与绘制：在应用端，
DecorView会触发展开 View 树的measure -> layout -> draw流程，将 Launcher 的图标、壁纸等元素绘制到Canvas中，并将数据填充到上述的 Surface 缓冲区。 - 请求显示（ApplySurface） ：绘制完成后，
WindowManager向系统WindowManagerService提交一个setTransaction请求，告知系统该窗口的 Surface 已经准备就绪，可以显示。 - SurfaceFlinger 合成：系统端的
SurfaceFlinger接收到缓冲区数据后，会将该 Surface 图层与状态栏、导航栏等图层进行合成，并最终输出到屏幕硬件上。此时，用户才能真正看到桌面。
