Activity/应用（O/8.0）启动流程（一）
Activity/应用（O/8.0）启动流程（二）
Activity/应用（O/8.0）启动流程（三）
Activity/应用（O/8.0）启动流程（四）
1） 将启动操作从用户进程传递到AMS进程，
我们平常启动一个Activity都是通过startActivity来进行操作，也是启动Activity的唯一操作，我们从桌面启动一个应用程序来说；
其实大家都知道桌面也是一个应用程序，通过PMS获取到所有的安装程序的信息，然后通过图标的进行展示，点击图标的时候然后进行跳转；
系统的桌面程序进行展示的Activity为LauncherActivity，通过监听点击事件进行跳转
// LauncherActivity#onListItemClick
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
Intent intent = intentForPosition(position);
startActivity(intent);
}
/**
* Return the actual Intent for a specific position in our
* {@link android.widget.ListView}.
* @param position The item whose Intent to return
*/
protected Intent intentForPosition(int position) {
ActivityAdapter adapter = (ActivityAdapter) mAdapter;
return adapter.intentForPosition(position);
}
ActivityAdapter里面存储着应用启动的信息，会通过下标获取这些信息并加入到Intent里面然后返回，这里就不在多说了。
然后调用startActivity，这么我们主要看Activity中的startActivity，
@Override
public void startActivity(Intent intent) {
this.startActivity(intent, null);
}
@Override
public void startActivity(Intent intent, @Nullable Bundle options) {
// 因为options为null，我们走else 从这里们可以看出 startActivity最终调用的还是startActivityForResult，
// 但是因为没有设置requestCode，默认都是-1，也可以说是<0的值；
if (options != null) {
startActivityForResult(intent, -1, options);
} else {
// Note we want to go through this call for compatibility with
// applications that may have overridden the method.
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) {
// 前面我们说options = null 所以这里会通过transferSpringboardActivityOptions去获取一个options
// 最终调用了Instrumentation#execStartActivity
options = transferSpringboardActivityOptions(options);
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) {
// 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;
}
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 {
// Note we want to go through this method for compatibility with
// existing applications that may have overridden it.
mParent.startActivityFromChild(this, intent, requestCode);
}
}
}
上面说到了会获取一个ActivityOptions 对象，这个对象的其他作用我们可能不知道，但是在页面跳转的时候的跳转动画会用到ActivityOptions
Pair pairSearch = Pair.create(vSearch,"search");
Pair pairIcon = Pair.create(ivIcon,"iconTransition");
Intent intent = new Intent(SearchTabActivity.this, SearchActivity.class);
getWindow().setSharedElementEnterTransition(transition);
ActivityOptions options = ActivityOptions.makeSceneTransitionAnimation(this,pairSearch,pairIcon);
startActivity(intent, options.toBundle());
我们来看Instrumentation中的execStartActivity，先来看下入参
who：执行启动的上下文环境，在Activity中的入参为this
contextThread: Activity对应的ApplicationThread
token: 每个Activity都有一个token，用于表示自身 ，在ActivityRecord创建的时候会一并创建
target: 代表执行启动的Activity，还有一点就是用于接收从将要启动的的Activity返回的信息，onActivityResult（）
// Instrumentation#execStartActivity
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);
}
// ... 代码省略
try {
intent.migrateExtraStreamToClipData();
intent.prepareToLeaveProcess(who);
int result = ActivityManager.getService()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
checkStartActivityResult(result, intent);
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
return null;
}
省略了一些代码，我们可以看到这里将一些初始参数传递到了AMS中，因为是AMS所在的进程与用户进程不是同一个进程，所以这里使用了Binder来实现了跨进程的调用，这里也不多说，下面直接看AMS中的处理。
2）在AMS中对参数初始化
同样先来看下入参
caller : 执行启动的Activity对应的ApplicationThread
callingPackage：执行启动的Activity的包名
resultTo：即上面所说的token
resultWho：Activity中的一个成员变量mEmbeddedID ，也可以理解为Activity独有的标识
接下来会调用这几个方法，因为都是直接调用，没有什么特别的参数，包括下面的流程，这种的代码我都会给一个调用流程，代码可能就不贴了
AMS.startActivity->AMS.startActivityAsUser -> ActivityStarter.startActivityMayWait
AMS#startActivityAsUser
@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, "startActivityAsUser");
}
因为这里新加了几个参数，为了让大家做好对比，就把方法贴出来了；同时此时PMS将参数传递到了ActivityStarter中
ActivityStarter#startActivityMayWait
final 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, Bundle bOptions, boolean ignoreTargetSecurity, int userId,
TaskRecord inTask, String reason) {
...代码省略
// 这里会通过PMS去解析Intent，得到一个ResolveInfo信息，里面包含有ActivityInfo、ServiceInfo等信息
ResolveInfo rInfo = mSupervisor.resolveIntent(intent, resolvedType, userId);
// Collect information about the target of the Intent.
// 根据解析出来的ResolveInfo，获取其中的ActivityInfo，即我们即将要启动的Activity信息
ActivityInfo aInfo = mSupervisor.resolveActivity(intent, rInfo, startFlags, profilerInfo);
.... 代码省略
ActivityOptions options = ActivityOptions.fromBundle(bOptions);
.... 代码省略
.... 代码省略
final ActivityRecord[] outRecord = new ActivityRecord[1];
int res = startActivityLocked(caller, intent, ephemeralIntent, resolvedType,
aInfo, rInfo, voiceSession, voiceInteractor,
resultTo, resultWho, requestCode, callingPid,
callingUid, callingPackage, realCallingPid, realCallingUid, startFlags,
options, ignoreTargetSecurity, componentSpecified, outRecord, inTask,
reason);
...代码省略
return res;
}
}
inTask上面传递过来是null，这里注意下
这个方法的作用就是解析Intent，得到将要启动的Activity的信息，解析的过程是在PMS中进行的，这里也就不再多说，感兴趣同学的可以进去看看。最后调用了startActivityLocked（） -> startActivity（） 。
// ActivityStarter#startActivity
/** DO NOT call this method directly. Use {@link #startActivityLocked} instead. */
private int startActivity(IApplicationThread caller, Intent intent, Intent ephemeralIntent,
String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid,
String callingPackage, int realCallingPid, int realCallingUid, int startFlags,
ActivityOptions options, boolean ignoreTargetSecurity, boolean componentSpecified,
ActivityRecord[] outActivity, TaskRecord inTask) {
// 初始化err的值
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;
ProcessRecord callerApp = null;
if (caller != null) {
// 获取执行启动的Activty所对应的ProcessRecord，在AMS中保存着一个ProcessRecord集合，存放着所有运行中的进程
callerApp = mService.getRecordForAppLocked(caller);
if (callerApp != null) {
callingPid = callerApp.pid;
callingUid = callerApp.info.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 ? 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) {
// 从ActivityStackSupervisor中遍历所有的栈中的所有ActivityRecord，找到与之对应的ActivityRecord，
// 这里返回的也就是执行启动的Activity所对应的ActivityRecord
sourceRecord = mSupervisor.isInAnyStackLocked(resultTo);
if (DEBUG_RESULTS) Slog.v(TAG_RESULTS,
"Will send result to " + resultTo + " " + sourceRecord);
if (sourceRecord != null) {
// 如果需要返回信息到原Activity 则将原Activity对应的ActivityRecord赋值给resultRecord
if (requestCode >= 0 && !sourceRecord.finishing) {
resultRecord = sourceRecord;
}
}
}
// ... 代码省略
// 获取原Activity对应的ActivityStatck
final ActivityStack resultStack = resultRecord == null ? null : resultRecord.getStack();
// 如果上面哪里执行错误，就会进入这个判断，通过ActivityStack.sendActivityResultLocked将原Actiivty执行暂停操作
if (err != START_SUCCESS) {
if (resultRecord != null) {
resultStack.sendActivityResultLocked(
-1, resultRecord, resultWho, requestCode, RESULT_CANCELED, null);
}
ActivityOptions.abort(options);
return err;
}
boolean abort = !mSupervisor.checkStartAnyActivityPermission(intent, aInfo, resultWho,
requestCode, callingPid, callingUid, callingPackage, ignoreTargetSecurity, callerApp,
resultRecord, resultStack, options);
abort |= !mService.mIntentFirewall.checkStartActivity(intent, callingUid,
callingPid, resolvedType, aInfo.applicationInfo);
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);
mInterceptor.intercept(intent, rInfo, aInfo, resolvedType, inTask, callingPid, callingUid,
options);
intent = mInterceptor.mIntent;
rInfo = mInterceptor.mRInfo;
aInfo = mInterceptor.mAInfo;
resolvedType = mInterceptor.mResolvedType;
inTask = mInterceptor.mInTask;
callingPid = mInterceptor.mCallingPid;
callingUid = mInterceptor.mCallingUid;
options = mInterceptor.mActivityOptions;
if (abort) {
if (resultRecord != null) {
resultStack.sendActivityResultLocked(-1, resultRecord, resultWho, requestCode,
RESULT_CANCELED, null);
}
// We pretend to the caller that it was really started, but
// they will just get a cancel result.
ActivityOptions.abort(options);
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 (mService.mPermissionReviewRequired && aInfo != null) {
if (mService.getPackageManagerInternalLocked().isPermissionsReviewRequired(
aInfo.packageName, userId)) {
IIntentSender target = mService.getIntentSenderLocked(
ActivityManager.INTENT_SENDER_ACTIVITY, callingPackage,
callingUid, userId, null, null, 0, new Intent[]{intent},
new String[]{resolvedType}, PendingIntent.FLAG_CANCEL_CURRENT
| PendingIntent.FLAG_ONE_SHOT, null);
final int flags = intent.getFlags();
Intent newIntent = new Intent(Intent.ACTION_REVIEW_PERMISSIONS);
newIntent.setFlags(flags
| Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS);
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;
resolvedType = null;
callingUid = realCallingUid;
callingPid = realCallingPid;
rInfo = mSupervisor.resolveIntent(intent, resolvedType, userId);
aInfo = mSupervisor.resolveActivity(intent, rInfo, startFlags,
null /*profilerInfo*/);
if (DEBUG_PERMISSIONS_REVIEW) {
Slog.i(TAG, "START u" + userId + " {" + intent.toShortString(true, true,
true, false) + "} from uid " + callingUid + " on display "
+ (mSupervisor.mFocusedStack == null
? DEFAULT_DISPLAY : mSupervisor.mFocusedStack.mDisplayId));
}
}
}
// 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, ephemeralIntent,
callingPackage, verificationBundle, resolvedType, userId);
resolvedType = null;
callingUid = realCallingUid;
callingPid = realCallingPid;
// 从ResultInfo中获取到对应的ActivityInfo
aInfo = mSupervisor.resolveActivity(intent, rInfo, startFlags, null /*profilerInfo*/);
}
// 创建一个包含被启动Activity信息的ActivityRecord
// 里面包含有AM，执行启动的Actiivty的进程信息、包名，被启动Activity的ActivityInfo等等
ActivityRecord r = new ActivityRecord(mService, callerApp, callingPid, callingUid,
callingPackage, intent, resolvedType, aInfo, mService.getGlobalConfiguration(),
resultRecord, resultWho, requestCode, componentSpecified, voiceSession != null,
mSupervisor, options, sourceRecord);
if (outActivity != null) {
outActivity[0] = 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;
}
// 获取到目前获取到焦点的栈
final ActivityStack stack = mSupervisor.mFocusedStack;
// 如果此栈中的的mResumedActivity == null（mResumedActivity 此时应该为执行启动的Activity）
// 或者mResumedActivity不等于执行启动的Activity，就会暂时取消启动 ，将要启动的Activity加入到等待队列中，
// 也就是mPendingActivityLaunches中
if (voiceSession == null && (stack.mResumedActivity == null
|| stack.mResumedActivity.info.applicationInfo.uid != callingUid)) {
if (!mService.checkAppSwitchAllowedLocked(callingPid, callingUid,
realCallingPid, realCallingUid, "Activity start")) {
PendingActivityLaunch pal = new PendingActivityLaunch(r,
sourceRecord, startFlags, stack, callerApp);
mPendingActivityLaunches.add(pal);
ActivityOptions.abort(options);
return ActivityManager.START_SWITCHES_CANCELED;
}
}
if (mService.mDidAppSwitch) {
// This is the second allowed switch since we stopped switches,
// so now just generally allow switches. Use case: user presses
// home (switches disabled, switch to home, mDidAppSwitch now true);
// user taps a home icon (coming from home so allowed, we hit here
// and now allow anyone to switch again).
mService.mAppSwitchesAllowedTime = 0;
} else {
mService.mDidAppSwitch = true;
}
// 这个方法是执行等待队列中的需要被启动的Activity，
doPendingActivityLaunchesLocked(false);
// 这里是执行启动的入口，当然doPendingActivityLaunchesLocked（）也会调用此方法
// 不同的地方就是这里传的 doResume = true，而上面的那个方法传的是false
return startActivity(r, sourceRecord, voiceSession, voiceInteractor, startFlags, true,
options, inTask, outActivity);
}
这个方法比较长，下面的流程中还有几个方法也比较长，处处是坑，一不小心就跑偏了，真是看得头疼
ActivityStarter#doPendingActivityLaunchesLocked
final void doPendingActivityLaunchesLocked(boolean doResume) {
// 遍历等待队列中的等待被启动的Activity信息，然后逐个启动
while (!mPendingActivityLaunches.isEmpty()) {
final PendingActivityLaunch pal = mPendingActivityLaunches.remove(0);
final boolean resume = doResume && mPendingActivityLaunches.isEmpty();
try {
startActivity(pal.r, pal.sourceRecord, null, null, pal.startFlags, resume, null,
null, null /*outRecords*/);
} catch (Exception e) {
Slog.e(TAG, "Exception during pending activity launch pal=" + pal, e);
pal.sendErrorResult(e.getMessage());
}
}
}
我们继续往下看 ActivityStarter#startActivity -> startActivityUnchecked，又是一个特别长的方法
3）为需要被启动的Activity设置栈信息
private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
ActivityRecord[] outActivity) {
// 初始化操作
setInitialState(r, options, inTask, doResume, startFlags, sourceRecord, voiceSession,
voiceInteractor);
// 解析启动模式
computeLaunchingTaskFlags();
// 获取原activity对应的ActivityStack
computeSourceStack();
mIntent.setFlags(mLaunchFlags);
// 复用ActivtiyRecord
ActivityRecord reusedActivity = getReusableIntentActivity();
final int preferredLaunchStackId =
(mOptions != null) ? mOptions.getLaunchStackId() : INVALID_STACK_ID;
final int preferredLaunchDisplayId =
(mOptions != null) ? mOptions.getLaunchDisplayId() : DEFAULT_DISPLAY;
if (reusedActivity != null) {
// 如果得到的复用的AcitivtyRecord不为空 ， 就为即将启动的Activity所对应的ActivityRecord设置task
// 为复用的ActivityRecord对应的task信息
// When the flags NEW_TASK and CLEAR_TASK are set, then the task gets reused but
// still needs to be a lock task mode violation since the task gets cleared out and
// the device would otherwise leave the locked task.
if (mSupervisor.isLockTaskModeViolation(reusedActivity.getTask(),
(mLaunchFlags & (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK))
== (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK))) {
mSupervisor.showLockTaskToast();
Slog.e(TAG, "startActivityUnchecked: Attempt to violate Lock Task Mode");
return START_RETURN_LOCK_TASK_MODE_VIOLATION;
}
if (mStartActivity.getTask() == null) {
// 为需要被启动的Activity设置栈信息
mStartActivity.setTask(reusedActivity.getTask());
}
if (reusedActivity.getTask().intent == null) {
// This task was started because of movement of the activity based on affinity...
// Now that we are actually launching it, we can assign the base intent.
reusedActivity.getTask().setIntent(mStartActivity);
}
// This code path leads to delivering a new intent, we want to make sure we schedule it
// as the first operation, in case the activity will be resumed as a result of later
// operations.
// 如果设置了FLAG_ACTIVITY_CLEAR_TOP这个标志，并且Activty的启动模式为SIGNLETASK或SINGLEINSTANCE，
// 在启动Activity的时候，如果在Activity历史栈中找到了与之一样的Activity，就会将旧的Activity上面的其他
// Activity执行出栈操作，并将此Activity至于栈顶，同时调用onNewIntent方法
if ((mLaunchFlags & FLAG_ACTIVITY_CLEAR_TOP) != 0
|| isDocumentLaunchesIntoExisting(mLaunchFlags)
|| mLaunchSingleInstance || mLaunchSingleTask) {
final TaskRecord task = reusedActivity.getTask();
// In this situation we want to remove all activities from the task up to the one
// being started. In most cases this means we are resetting the task to its initial
// state.
// 执行清除栈的操作 并返回栈中与之一样的ActivityReocrd
final ActivityRecord top = task.performClearTaskForReuseLocked(mStartActivity,
mLaunchFlags);
// The above code can remove {@code reusedActivity} from the task, leading to the
// the {@code ActivityRecord} removing its reference to the {@code TaskRecord}. The
// task reference is needed in the call below to
// {@link setTargetStackAndMoveToFrontIfNeeded}.
if (reusedActivity.getTask() == null) {
reusedActivity.setTask(task);
}
if (top != null) {
if (top.frontOfTask) {
// Activity aliases may mean we use different intents for the top activity,
// so make sure the task now has the identity of the new intent.
top.getTask().setIntent(mStartActivity);
}
// 调用onNewIntent方法
deliverNewIntent(top);
}
}
sendPowerHintForLaunchStartIfNeeded(false /* forceSend */, reusedActivity);
// 将复用的ActivityRecord对应的ActivityStack移动到前台（此时当前获取到焦点的栈为此Activity所对应的栈 ）
reusedActivity = setTargetStackAndMoveToFrontIfNeeded(reusedActivity);
final ActivityRecord outResult =
outActivity != null && outActivity.length > 0 ? outActivity[0] : null;
// When there is a reused activity and the current result is a trampoline activity,
// set the reused activity as the result.
if (outResult != null && (outResult.finishing || outResult.noDisplay)) {
outActivity[0] = reusedActivity;
}
// 如果设置了START_RETURN_INTENT_TO_CALLER 那么直接调用该Activity的onResume 而不需要重新启动
if ((mStartFlags & START_FLAG_ONLY_IF_NEEDED) != 0) {
// We don't need to start a new activity, and the client said not to do anything
// if that is the case, so this is it! And for paranoia, make sure we have
// correctly resumed the top activity.
resumeTargetStackIfNeeded();
return START_RETURN_INTENT_TO_CALLER;
}
setTaskFromIntentActivity(reusedActivity);
// 如果设置了SINGLETASK/SINGLEINSTANCE 那么也不需要重新启动Activity，直接调用其onResume
if (!mAddingToTask && mReuseTask == null) {
// We didn't do anything... but it was needed (a.k.a., client don't use that
// intent!) And for paranoia, make sure we have correctly resumed the top activity.
resumeTargetStackIfNeeded();
if (outActivity != null && outActivity.length > 0) {
outActivity[0] = reusedActivity;
}
return START_TASK_TO_FRONT;
}
}
if (mStartActivity.packageName == null) {
final ActivityStack sourceStack = mStartActivity.resultTo != null
? mStartActivity.resultTo.getStack() : null;
if (sourceStack != null) {
// 这里是执行启动的Activity执行onPause操作
sourceStack.sendActivityResultLocked(-1 /* callingUid */, mStartActivity.resultTo,
mStartActivity.resultWho, mStartActivity.requestCode, RESULT_CANCELED,
null /* data */);
}
ActivityOptions.abort(mOptions);
return START_CLASS_NOT_FOUND;
}
// If the activity being launched is the same as the one currently at the top, then
// we need to check if it should only be launched once.
final ActivityStack topStack = mSupervisor.mFocusedStack;
final ActivityRecord topFocused = topStack.topActivity();
final ActivityRecord top = topStack.topRunningNonDelayedActivityLocked(mNotTop);
final boolean dontStart = top != null && mStartActivity.resultTo == null
&& top.realActivity.equals(mStartActivity.realActivity)
&& top.userId == mStartActivity.userId
&& top.app != null && top.app.thread != null
&& ((mLaunchFlags & FLAG_ACTIVITY_SINGLE_TOP) != 0
|| mLaunchSingleTop || mLaunchSingleTask);
if (dontStart) {
// For paranoia, make sure we have correctly resumed the top activity.
topStack.mLastPausedActivity = null;
// 上面说了 传入的doResume == true，虽然在setInitialState进行了初始化 但还是为true
if (mDoResume) {
// 这个方法有点绕 后面再说
mSupervisor.resumeFocusedStackTopActivityLocked();
}
ActivityOptions.abort(mOptions);
if ((mStartFlags & START_FLAG_ONLY_IF_NEEDED) != 0) {
// We don't need to start a new activity, and the client said not to do
// anything if that is the case, so this is it!
return START_RETURN_INTENT_TO_CALLER;
}
// 如果将要启动的Activity是SINGLTOP模式的 并且当前执行启动的Activity与要被启动的一致 那么调用其onNewIntent方法
deliverNewIntent(top);
// Don't use mStartActivity.task to show the toast. We're not starting a new activity
// but reusing 'top'. Fields in mStartActivity may not be fully initialized.
mSupervisor.handleNonResizableTaskIfNeeded(top.getTask(), preferredLaunchStackId,
preferredLaunchDisplayId, topStack.mStackId);
return START_DELIVERED_TO_TOP;
}
boolean newTask = false;
final TaskRecord taskToAffiliate = (mLaunchTaskBehind && mSourceRecord != null)
? mSourceRecord.getTask() : null;
// Should this be considered a new task?
int result = START_SUCCESS;
// 这里是为要被启动的Activity设置一个ActivityStack，并指定给mTargetStack
if (mStartActivity.resultTo == null && mInTask == null && !mAddingToTask
&& (mLaunchFlags & FLAG_ACTIVITY_NEW_TASK) != 0) {
newTask = true;
// 这里是创建一个新的TaskRecord
result = setTaskFromReuseOrCreateNewTask(
taskToAffiliate, preferredLaunchStackId, topStack);
} else if (mSourceRecord != null) {
// 设置与启动Activity一样的栈
result = setTaskFromSourceRecord();
} else if (mInTask != null) {
result = setTaskFromInTask();
} else {
// This not being started from an existing activity, and not part of a new task...
// just put it in the top task, though these days this case should never happen.
setTaskToCurrentTopOrCreateNewTask();
}
if (result != START_SUCCESS) {
return result;
}
mService.grantUriPermissionFromIntentLocked(mCallingUid, mStartActivity.packageName,
mIntent, mStartActivity.getUriPermissionsLocked(), mStartActivity.userId);
mService.grantEphemeralAccessLocked(mStartActivity.userId, mIntent,
mStartActivity.appInfo.uid, UserHandle.getAppId(mCallingUid));
if (mSourceRecord != null) {
mStartActivity.getTask().setTaskToReturnTo(mSourceRecord);
}
if (newTask) {
EventLog.writeEvent(
EventLogTags.AM_CREATE_TASK, mStartActivity.userId,
mStartActivity.getTask().taskId);
}
ActivityStack.logStartActivity(
EventLogTags.AM_CREATE_ACTIVITY, mStartActivity, mStartActivity.getTask());
mTargetStack.mLastPausedActivity = null;
sendPowerHintForLaunchStartIfNeeded(false /* forceSend */, mStartActivity);
// 这里可以暂且理解为为新Activity设置statck
mTargetStack.startActivityLocked(mStartActivity, topFocused, newTask, mKeepCurTransition,
mOptions);
if (mDoResume) {
final ActivityRecord topTaskActivity =
mStartActivity.getTask().topRunningActivityLocked();
if (!mTargetStack.isFocusable()
|| (topTaskActivity != null && topTaskActivity.mTaskOverlay
&& mStartActivity != topTaskActivity)) {
// If the activity is not focusable, we can't resume it, but still would like to
// make sure it becomes visible as it starts (this will also trigger entry
// animation). An example of this are PIP activities.
// Also, we don't want to resume activities in a task that currently has an overlay
// as the starting activity just needs to be in the visible paused state until the
// over is removed.
mTargetStack.ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
// Go ahead and tell window manager to execute app transition for this activity
// since the app transition will not be triggered through the resume channel.
mWindowManager.executeAppTransition();
} else {
// If the target stack was not previously focusable (previous top running activity
// on that stack was not visible) then any prior calls to move the stack to the
// will not update the focused stack. If starting the new activity now allows the
// task stack to be focusable, then ensure that we now update the focused stack
// accordingly.
if (mTargetStack.isFocusable() && !mSupervisor.isFocusedStack(mTargetStack)) {
// 将目标栈移动到前台 即设置为可以获取到焦点的栈
mTargetStack.moveToFront("startActivityUnchecked");
}
// 通常都会走到这里
mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity,
mOptions);
}
} else {
mTargetStack.addRecentActivityLocked(mStartActivity);
}
mSupervisor.updateUserStackLocked(mStartActivity.userId, mTargetStack);
mSupervisor.handleNonResizableTaskIfNeeded(mStartActivity.getTask(), preferredLaunchStackId,
preferredLaunchDisplayId, mTargetStack.mStackId);
return START_SUCCESS;
}
这个方法很长，也很绕，我们一点点来说
- setInitialState（）是初始化参数
mStartActivity为我们要启动的Activity所代表的ActivityRecord
mSourceRecord为我们执行启动的Activity所代表的ActivityRecord
mDoResume值为true - getReusableIntentActivity（）查找有没有可以替代需要被启动的Activity的Activity
// ActivityStarter#getReusableIntentActivity：
private ActivityRecord getReusableIntentActivity() {
// We may want to try to place the new activity in to an existing task. We always
// do this if the target activity is singleTask or singleInstance; we will also do
// this if NEW_TASK has been requested, and there is not an additional qualifier telling
// us to still place it in a new task: multi task, always doc mode, or being asked to
// launch this as a new task behind the current one.
boolean putIntoExistingTask = ((mLaunchFlags & FLAG_ACTIVITY_NEW_TASK) != 0 &&
(mLaunchFlags & FLAG_ACTIVITY_MULTIPLE_TASK) == 0)
|| mLaunchSingleInstance || mLaunchSingleTask;
// If bring to front is requested, and no result is requested and we have not been given
// an explicit task to launch in to, and we can find a task that was started with this
// same component, then instead of launching bring that one to the front.
putIntoExistingTask &= mInTask == null && mStartActivity.resultTo == null;
ActivityRecord intentActivity = null;
if (mOptions != null && mOptions.getLaunchTaskId() != -1) {
// 这个分支一般不会进入，mOptions就是我们开篇说到的ActivityOptions，不为空，但是只有当明确知道将要启动的Activity在那个具体的task中才会为LanucherTaskId设置值，一般情况为-1；
final TaskRecord task = mSupervisor.anyTaskForIdLocked(mOptions.getLaunchTaskId());
intentActivity = task != null ? task.getTopActivity() : null;
} else if (putIntoExistingTask) {
if (mLaunchSingleInstance) {
// 对应SIGNLEINSTANCE 这里会在所有的stack中以及其所有的task以及其中的activity
// There can be one and only one instance of single instance activity in the
// history, and it is always in its own unique task, so we do a special search.
intentActivity = mSupervisor.findActivityLocked(mIntent, mStartActivity.info,
mStartActivity.isHomeActivity());
} else if ((mLaunchFlags & FLAG_ACTIVITY_LAUNCH_ADJACENT) != 0) {
//这个用在多窗口的分屏中，指定显示activity挨着打开这个activity的旁边
// For the launch adjacent case we only want to put the activity in an existing
// task if the activity already exists in the history.
intentActivity = mSupervisor.findActivityLocked(mIntent, mStartActivity.info,
!mLaunchSingleTask);
} else {
// 遍历所有的stack里面的每个task，找到其top的Activity，并于即将要启动的Activity做比较
// Otherwise find the best task to put the activity in.
intentActivity = mSupervisor.findTaskLocked(mStartActivity, mSourceDisplayId);
}
}
return intentActivity;
}
我们先来看findActivityLocked
// ActivityStackSupervisor#findActivityLocked
ActivityRecord findActivityLocked(Intent intent, ActivityInfo info,
boolean compareIntentFilters) {
// 遍历ActivityDisplays集合中的所有ActivityStack集合
// 得到每一个ActivityStack，然后再去与其中储存的ActivityRecord进行对比
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
final ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
final ActivityRecord ar = stacks.get(stackNdx)
.findActivityLocked(intent, info, compareIntentFilters);
if (ar != null) {
return ar;
}
}
}
return null;
}
// ActivityStack#findActivityLocked
ActivityRecord findActivityLocked(Intent intent, ActivityInfo info,
boolean compareIntentFilters) {
ComponentName cls = intent.getComponent();
if (info.targetActivity != null) {
cls = new ComponentName(info.packageName, info.targetActivity);
}
final int userId = UserHandle.getUserId(info.applicationInfo.uid);
// 遍历ActivityStack中的历史栈TaskRecord，将得到的ActivityRecord与历史栈中的ActivityRecord进行对比
for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
final TaskRecord task = mTaskHistory.get(taskNdx);
final ArrayList<ActivityRecord> activities = task.mActivities;
for (int activityNdx = activities.size() - 1; activityNdx >= 0; --activityNdx) {
ActivityRecord r = activities.get(activityNdx);
if (!r.okToShowLocked()) {
continue;
}
// 如果历史栈中的Activity没有被销毁，并且是同一用户空间（针对Android的多用户模式，这里可以忽略）
if (!r.finishing && r.userId == userId) {
if (compareIntentFilters) {
// 然后将两者的Intent信息进行比较，如果相同则返回如果不相同则继续遍历
if (r.intent.filterEquals(intent)) {
return r;
}
} else {
if (r.intent.getComponent().equals(cls)) {
return r;
}
}
}
}
}
return null;
}
// 具体比较的Intent信息如下，我们都知道隐式启动Activity会传入Action、Data、Categories等，所以这里比较的就是这些数据
public boolean filterEquals(Intent other) {
if (other == null) {
return false;
}
if (!Objects.equals(this.mAction, other.mAction)) return false;
if (!Objects.equals(this.mData, other.mData)) return false;
if (!Objects.equals(this.mType, other.mType)) return false;
if (!Objects.equals(this.mPackage, other.mPackage)) return false;
if (!Objects.equals(this.mComponent, other.mComponent)) return false;
if (!Objects.equals(this.mCategories, other.mCategories)) return false;
return true;
}
我们再来看最后一个else中的ActivityStackSupervisor#findTaskLocked
ActivityRecord findTaskLocked(ActivityRecord r, int displayId) {
mTmpFindTaskResult.r = null;
mTmpFindTaskResult.matchedByRootAffinity = false;
ActivityRecord affinityMatch = null;
if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Looking for task of " + r);
// 首先也是遍历ActivityDisplays集合，得到其中的ActivityStack集合，然后再继续遍历ActivityStack集合
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
final ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
final ActivityStack stack = stacks.get(stackNdx);
if (!checkActivityBelongsInStack(r, stack)) {
if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Skipping stack: (mismatch activity/stack) "
+ stack);
continue;
}
// 对遍历到的每一个Stack调用其findTaskLocked（）
stack.findTaskLocked(r, mTmpFindTaskResult);
// It is possible to have tasks in multiple stacks with the same root affinity, so
// we should keep looking after finding an affinity match to see if there is a
// better match in another stack. Also, task affinity isn't a good enough reason
// to target a display which isn't the source of the intent, so skip any affinity
// matches not on the specified display.
if (mTmpFindTaskResult.r != null) {
if (!mTmpFindTaskResult.matchedByRootAffinity) {
return mTmpFindTaskResult.r;
} else if (mTmpFindTaskResult.r.getDisplayId() == displayId) {
// Note: since the traversing through the stacks is top down, the floating
// tasks should always have lower priority than any affinity-matching tasks
// in the fullscreen stacks
affinityMatch = mTmpFindTaskResult.r;
}
}
}
}
if (DEBUG_TASKS && affinityMatch == null) Slog.d(TAG_TASKS, "No task found");
return affinityMatch;
}
// ActivityStack#findTaskLocked
void findTaskLocked(ActivityRecord target, FindTaskResult result) {
Intent intent = target.intent;
ActivityInfo info = target.info;
ComponentName cls = intent.getComponent();
if (info.targetActivity != null) {
cls = new ComponentName(info.packageName, info.targetActivity);
}
final int userId = UserHandle.getUserId(info.applicationInfo.uid);
boolean isDocument = intent != null & intent.isDocument();
// If documentData is non-null then it must match the existing task data.
Uri documentData = isDocument ? intent.getData() : null;
if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Looking for task of " + target + " in " + this);
// 遍历ActivityStack中的TaskRecord集合，
for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) {
final TaskRecord task = mTaskHistory.get(taskNdx);
if (task.voiceSession != null) {
// We never match voice sessions; those always run independently.
if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Skipping " + task + ": voice session");
continue;
}
if (task.userId != userId) {
// Looking for a different task.
if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Skipping " + task + ": different user");
continue;
}
// Overlays should not be considered as the task's logical top activity.
// 得到TaskRecord集中的顶部Activity 并与将要启动的Activity做比较
final ActivityRecord r = task.getTopActivity(false /* includeOverlays */);
if (r == null || r.finishing || r.userId != userId ||
r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Skipping " + task + ": mismatch root " + r);
continue;
}
if (r.mActivityType != target.mActivityType) {
if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Skipping " + task + ": mismatch activity type");
continue;
}
final Intent taskIntent = task.intent;
final Intent affinityIntent = task.affinityIntent;
final boolean taskIsDocument;
final Uri taskDocumentData;
if (taskIntent != null && taskIntent.isDocument()) {
taskIsDocument = true;
taskDocumentData = taskIntent.getData();
} else if (affinityIntent != null && affinityIntent.isDocument()) {
taskIsDocument = true;
taskDocumentData = affinityIntent.getData();
} else {
taskIsDocument = false;
taskDocumentData = null;
}
if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Comparing existing cls="
+ taskIntent.getComponent().flattenToShortString()
+ "/aff=" + r.getTask().rootAffinity + " to new cls="
+ intent.getComponent().flattenToShortString() + "/aff=" + info.taskAffinity);
// TODO Refactor to remove duplications. Check if logic can be simplified.
// 然后比较两者的Component，如果相同则赋值给result，因为在findTaskLocked中会用到
if (taskIntent != null && taskIntent.getComponent() != null &&
taskIntent.getComponent().compareTo(cls) == 0 &&
Objects.equals(documentData, taskDocumentData)) {
if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Found matching class!");
//dump();
if (DEBUG_TASKS) Slog.d(TAG_TASKS,
"For Intent " + intent + " bringing to top: " + r.intent);
result.r = r;
result.matchedByRootAffinity = false;
break;
} else if (affinityIntent != null && affinityIntent.getComponent() != null &&
affinityIntent.getComponent().compareTo(cls) == 0 &&
Objects.equals(documentData, taskDocumentData)) {
if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Found matching class!");
//dump();
if (DEBUG_TASKS) Slog.d(TAG_TASKS,
"For Intent " + intent + " bringing to top: " + r.intent);
result.r = r;
result.matchedByRootAffinity = false;
break;
} else if (!isDocument && !taskIsDocument
&& result.r == null && task.rootAffinity != null) {
if (task.rootAffinity.equals(target.taskAffinity)) {
if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Found matching affinity candidate!");
// It is possible for multiple tasks to have the same root affinity especially
// if they are in separate stacks. We save off this candidate, but keep looking
// to see if there is a better candidate.
result.r = r;
result.matchedByRootAffinity = true;
}
} else if (DEBUG_TASKS) Slog.d(TAG_TASKS, "Not a match: " + task);
}
}
// ComponentName#compareTo
public int compareTo(ComponentName that) {
int v;
// 主要是比较包名和类名 如果两者相同则返回0
v = this.mPackage.compareTo(that.mPackage);
if (v != 0) {
return v;
}
return this.mClass.compareTo(that.mClass);
}
我们来捋一下getReusableIntentActivity（）：
getReusableIntentActivity（）总的来说是查找历史栈中是否存在与需要被启动的Activity一样的Activity，如果有则直接返回复用，没有则返回null。（复用的意思就是不会重新创建，而是直接跳转到）
1）首先对于SINGLEINSTANCE类型的Activity，需要遍历所有的ActivityStack中的所有TaskRecord中的ActivityRecord，如果某一个ActivityRecord中的Intent中的Action、Data、Categories等相同，则认定为是同一个ActivityRecord，可以复用
2）对于SIGNTOP类型的Activity来说会遍历TaskRecord找到其顶部的ActivityRecord，并与需要被启动的Activity对比类名和包名，如果相同则返回
（貌似拉下了singleTask的情况，按理说对于singleTask类型，应该也会类似于single Instance所有的栈进行遍历，但是前面却加了判断是否是single Instace的情况，那就是在else里面，但是最后else却是只取栈顶的activityrecord，所以我感觉应该是如果single Instance，那么必定为single Task）
好了我们返回ActivityStarter#startActivityUnchecked（）中继续看
- 如果找到了复用的ActivityReocrd（下面的几点都是针对如果有找到了复用的activity来说的）
1）先是将复用的ActivityRecord中的信息赋值到等待被启动的ActivityRecord中，比如说栈、intent等，然后将此栈移动到前台，也就是获取到焦点
2）往下继续就会调用setTaskFromIntentActivity（），入参为复用的Activity
private void setTaskFromIntentActivity(ActivityRecord intentActivity) {
if ((mLaunchFlags & (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK))
== (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK)) {
// 好多标识虽然看不懂但是通过注释和FLAG_ACTIVITY_NEW_TASK ，我们可以判断如果是要开启一个新的任务栈
// 就会进入这个方法
// The caller has requested to completely replace any existing task with its new
// activity. Well that should not be too hard...
// Note: we must persist the {@link TaskRecord} first as intentActivity could be
// removed from calling performClearTaskLocked (For example, if it is being brought out
// of history or if it is finished immediately), thus disassociating the task. Also note
// that mReuseTask is reset as a result of {@link TaskRecord#performClearTaskLocked}
// launching another activity.
// TODO(b/36119896): We shouldn't trigger activity launches in this path since we are
// already launching one.
final TaskRecord task = intentActivity.getTask();
// 这里会将此任务栈中的所有ActivityRecord清除掉 代码就不贴了
task.performClearTaskLocked();
mReuseTask = task;
mReuseTask.setIntent(mStartActivity);
// When we clear the task - focus will be adjusted, which will bring another task
// to top before we launch the activity we need. This will temporary swap their
// mTaskToReturnTo values and we don't want to overwrite them accidentally.
mMovedOtherTask = true;
} else if ((mLaunchFlags & FLAG_ACTIVITY_CLEAR_TOP) != 0
|| mLaunchSingleInstance || mLaunchSingleTask) {
// 如果是single instance 或者是singletask 也会清除掉任务栈中的AcitivityRecord，但是只清除此ActivityRecord顶部的ActivityRecord 代码就不贴了
ActivityRecord top = intentActivity.getTask().performClearTaskLocked(mStartActivity,
mLaunchFlags);
if (top == null) {
// A special case: we need to start the activity because it is not currently
// running, and the caller has asked to clear the current task to have this
// activity at the top.
mAddingToTask = true;
// We are no longer placing the activity in the task we previously thought we were.
mStartActivity.setTask(null);
// Now pretend like this activity is being started by the top of its task, so it
// is put in the right place.
mSourceRecord = intentActivity;
final TaskRecord task = mSourceRecord.getTask();
if (task != null && task.getStack() == null) {
// Target stack got cleared when we all activities were removed above.
// Go ahead and reset it.
mTargetStack = computeStackFocus(mSourceRecord, false /* newTask */,
null /* bounds */, mLaunchFlags, mOptions);
mTargetStack.addTask(task,
!mLaunchTaskBehind /* toTop */, "startActivityUnchecked");
}
}
} else if (mStartActivity.realActivity.equals(intentActivity.getTask().realActivity)) {
// In this case the top activity on the task is the same as the one being launched,
// so we take that as a request to bring the task to the foreground. If the top
// activity in the task is the root activity, deliver this new intent to it if it
// desires.
// 如果栈顶的ActivityRecord与需要被启动的Actiivty一致
if (((mLaunchFlags & FLAG_ACTIVITY_SINGLE_TOP) != 0 || mLaunchSingleTop)
&& intentActivity.realActivity.equals(mStartActivity.realActivity)) {
// 并如果是singtop类型的
if (intentActivity.frontOfTask) {
intentActivity.getTask().setIntent(mStartActivity);
}
会调用其onNewIntent方法
deliverNewIntent(intentActivity);
} else if (!intentActivity.getTask().isSameIntentFilter(mStartActivity)) {
// In this case we are launching the root activity of the task, but with a
// different intent. We should start a new instance on top.
mAddingToTask = true;
mSourceRecord = intentActivity;
}
} else if ((mLaunchFlags & FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) == 0) {
// In this case an activity is being launched in to an existing task, without
// resetting that task. This is typically the situation of launching an activity
// from a notification or shortcut. We want to place the new activity on top of the
// current task.
mAddingToTask = true;
mSourceRecord = intentActivity;
} else if (!intentActivity.getTask().rootWasReset) {
// In this case we are launching into an existing task that has not yet been started
// from its front door. The current task has been brought to the front. Ideally,
// we'd probably like to place this new task at the bottom of its stack, but that's
// a little hard to do with the current organization of the code so for now we'll
// just drop it.
intentActivity.getTask().setIntent(mStartActivity);
}
}
3）在往下就会调用ActivityStackSupervisor#resumeFocusedStackTopActivityLocked去进行启动这个放到后面再说
以上就是有复用ActivityRecord的情况，我们继续分析startActivityUnchecked（），
- 获取当前由焦点的栈，以及此栈栈顶的ActivityRecord，并判断是否与执行启动的ActivityRecord相同（一般都是同一个），并且如果是singletop/singleInstance/singleTask标识，会调用ActivityStackSupervisor#resumeFocusedStackTopActivityLocked（这个放在后面分析）并且会调用其onNewIntent（），然后结束返回;
*如果即没有可复用的ActivityRecord，并且启动模式也不是singtop，那么就需要我们新建一个task栈或者找到一个该activity所需要的栈
if (mStartActivity.resultTo == null && mInTask == null && !mAddingToTask
&& (mLaunchFlags & FLAG_ACTIVITY_NEW_TASK) != 0) {
newTask = true;
result = setTaskFromReuseOrCreateNewTask(
taskToAffiliate, preferredLaunchStackId, topStack);
} else if (mSourceRecord != null) {
result = setTaskFromSourceRecord();
} else if (mInTask != null) {
result = setTaskFromInTask();
} else {
// This not being started from an existing activity, and not part of a new task...
// just put it in the top task, though these days this case should never happen.
setTaskToCurrentTopOrCreateNewTask();
}
（栈的创建，会放在文末来说）
上面的判断，如果没有设置返回数据的activity并且inTask == null 以及有FLAG_ACTIVITY_NEW_TASK那我们就需要创建一个新栈，否则就根据相应的条件判断，是用启动activity的栈，还是用传递进来的新栈inStack还是用当前顶部的栈或者创建一个新栈，如果是新建一个TaskRecord就需要将新建的栈保存到ActivityStack中。
- 继续往下看
// mDoResume == true
if (mDoResume) {
// 获取待启动的Activity所在栈的顶部Activity(其实也就是需要被启动的Activity)
final ActivityRecord topTaskActivity =
mStartActivity.getTask().topRunningActivityLocked();
// 上面说了将此栈移动到前台，也就是获取到了焦点，并且两个Activity是同一个，所以会走else
if (!mTargetStack.isFocusable()
|| (topTaskActivity != null && topTaskActivity.mTaskOverlay
&& mStartActivity != topTaskActivity)) {
// If the activity is not focusable, we can't resume it, but still would like to
// make sure it becomes visible as it starts (this will also trigger entry
// animation). An example of this are PIP activities.
// Also, we don't want to resume activities in a task that currently has an overlay
// as the starting activity just needs to be in the visible paused state until the
// over is removed.
mTargetStack.ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
// Go ahead and tell window manager to execute app transition for this activity
// since the app transition will not be triggered through the resume channel.
mWindowManager.executeAppTransition();
} else {
// If the target stack was not previously focusable (previous top running activity
// on that stack was not visible) then any prior calls to move the stack to the
// will not update the focused stack. If starting the new activity now allows the
// task stack to be focusable, then ensure that we now update the focused stack
// accordingly.
if (mTargetStack.isFocusable() && !mSupervisor.isFocusedStack(mTargetStack)) {
// 这里将ActivityStackSupervisor中的此栈的状态设置为获取到焦点转台
mTargetStack.moveToFront("startActivityUnchecked");
}
mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity,
mOptions);
}
} else {
mTargetStack.addRecentActivityLocked(mStartActivity);
}
上面在说复用activity的时候也谈到了resumeFocusedStackTopActivityLocked，singtop模式的时候也说到了resumeFocusedStackTopActivityLocked，现在这里也用到了，碍于过长篇幅，简书有长度限制，我们新开一篇来说。本篇就到这里了。
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