startActivity启动过程分析
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copy from : http://gityuan.com/2016/03/12/start-activity/
基于android 6.0的源码剖析， 分析android Activity启动流程，相关源码：
frameworks/base/services/core/java/com/android/server/am/
- ActivityManagerService.java
- ActivityStackSupervisor.java
- ActivityStack.java
- ActivityRecord.java
- ProcessRecord.java
frameworks/base/core/java/android/app/
- IActivityManager.java
- ActivityManagerNative.java (内含AMP)
- ActivityManager.java
- IApplicationThread.java
- ApplicationThreadNative.java (内含ATP)
- ActivityThread.java (内含ApplicationThread)
- ContextImpl.java
一. 概述
startActivity的整体流程与startService启动过程分析非常相近，但比Service启动更为复杂，多了stack/task以及UI的相关内容以及Activity的生命周期更为丰富。
Activity启动发起后，通过Binder最终交由system进程中的AMS来完成，则启动流程如下图：
接下来，从源码来说说每个过程。
二. 启动流程
2.1 Activity.startActivity
[-> Activity.java]
public void startActivity(Intent intent) {
this.startActivity(intent, null);
}
public void startActivity(Intent intent, @Nullable Bundle options) {
if (options != null) {
startActivityForResult(intent, -1, options);
} else {
//[见小节2.2]
startActivityForResult(intent, -1);
}
}
2.2 startActivityForResult
[-> Activity.java]
public void startActivityForResult(Intent intent, int requestCode) {
startActivityForResult(intent, requestCode, null);
}
public void startActivityForResult(Intent intent, int requestCode, @Nullable Bundle options) {
if (mParent == null) {
//[见小节2.3]
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());
}
//此时requestCode =-1
if (requestCode >= 0) {
mStartedActivity = true;
}
cancelInputsAndStartExitTransition(options);
} else {
...
}
}
execStartActivity()方法的参数:
mAppThread: 数据类型为ApplicationThread，通过mMainThread.getApplicationThread()方法获取。mToken: 数据类型为IBinder.
2.3 execStartActivity
[-> Instrumentation.java]
public ActivityResult execStartActivity( Context who, IBinder contextThread, IBinder token, Activity target, Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
...
if (mActivityMonitors != null) {
synchronized (mSync) {
final int N = mActivityMonitors.size();
for (int i=0; i<N; i++) {
final ActivityMonitor am = mActivityMonitors.get(i);
if (am.match(who, null, intent)) {
am.mHits++;
//当该monitor阻塞activity启动,则直接返回
if (am.isBlocking()) {
return requestCode >= 0 ? am.getResult() : null;
}
break;
}
}
}
}
try {
intent.migrateExtraStreamToClipData();
intent.prepareToLeaveProcess();
//[见小节2.4]
int result = ActivityManagerNative.getDefault()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
//检查activity是否启动成功
checkStartActivityResult(result, intent);
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
return null;
}
关于 ActivityManagerNative.getDefault()返回的是ActivityManagerProxy对象. 此处startActivity()的共有10个参数, 下面说说每个参数传递AMP.startActivity()每一项的对应值:
- caller: 当前应用的ApplicationThread对象mAppThread;
- callingPackage: 调用当前ContextImpl.getBasePackageName(),获取当前Activity所在包名;
- intent: 这便是启动Activity时,传递过来的参数;
- resolvedType: 调用intent.resolveTypeIfNeeded而获取;
- resultTo: 来自于当前Activity.mToken
- resultWho: 来自于当前Activity.mEmbeddedID
- requestCode = -1;
- startFlags = 0;
- profilerInfo = null;
- options = null;
2.4 AMP.startActivity
[-> ActivityManagerNative.java :: ActivityManagerProxy]
class ActivityManagerProxy implements IActivityManager {
...
public int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle options) throws RemoteException {
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(caller != null ? caller.asBinder() : null);
data.writeString(callingPackage);
intent.writeToParcel(data, 0);
data.writeString(resolvedType);
data.writeStrongBinder(resultTo);
data.writeString(resultWho);
data.writeInt(requestCode);
data.writeInt(startFlags);
if (profilerInfo != null) {
data.writeInt(1);
profilerInfo.writeToParcel(data, Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
} else {
data.writeInt(0);
}
if (options != null) {
data.writeInt(1);
options.writeToParcel(data, 0);
} else {
data.writeInt(0);
}
//[见流程2.5]
mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);
reply.readException();
int result = reply.readInt();
reply.recycle();
data.recycle();
return result;
}
...
}
AMP经过binder IPC,进入ActivityManagerNative(简称AMN)。接下来程序进入了system_servr进程，开始继续执行。
2.5 AMN.onTransact
[-> ActivityManagerNative.java]
public boolean onTransact(int code, Parcel data, Parcel reply, int flags) throws RemoteException {
switch (code) {
case START_ACTIVITY_TRANSACTION:
{
data.enforceInterface(IActivityManager.descriptor);
IBinder b = data.readStrongBinder();
IApplicationThread app = ApplicationThreadNative.asInterface(b);
String callingPackage = data.readString();
Intent intent = Intent.CREATOR.createFromParcel(data);
String resolvedType = data.readString();
IBinder resultTo = data.readStrongBinder();
String resultWho = data.readString();
int requestCode = data.readInt();
int startFlags = data.readInt();
ProfilerInfo profilerInfo = data.readInt() != 0
? ProfilerInfo.CREATOR.createFromParcel(data) : null;
Bundle options = data.readInt() != 0
? Bundle.CREATOR.createFromParcel(data) : null;
//[见流程2.6]
int result = startActivity(app, callingPackage, intent, resolvedType,
resultTo, resultWho, requestCode, startFlags, profilerInfo, options);
reply.writeNoException();
reply.writeInt(result);
return true;
}
...
} }
2.6 AMS.startActivity
[-> ActivityManagerService.java]
public final int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle options) {
return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
resultWho, requestCode, startFlags, profilerInfo, options,
UserHandle.getCallingUserId());
}
public final int startActivityAsUser(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle options, int userId) {
enforceNotIsolatedCaller("startActivity");
userId = handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId,
false, ALLOW_FULL_ONLY, "startActivity", null);
//[见小节2.7]
return mStackSupervisor.startActivityMayWait(caller, -1, callingPackage, intent,
resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
profilerInfo, null, null, options, false, userId, null, null);
}
此处mStackSupervisor的数据类型为ActivityStackSupervisor
2.7 ASS.startActivityMayWait
当程序运行到这里时, ASS.startActivityMayWait的各个参数取值如下:
- caller = ApplicationThreadProxy, 用于跟调用者进程ApplicationThread进行通信的binder代理类.
- callingUid = -1;
- callingPackage = ContextImpl.getBasePackageName(),获取调用者Activity所在包名
- intent: 这是启动Activity时传递过来的参数;
- resolvedType = intent.resolveTypeIfNeeded
- voiceSession = null;
- voiceInteractor = null;
- resultTo = Activity.mToken, 其中Activity是指调用者所在Activity, mToken对象保存自己所处的ActivityRecord信息
- resultWho = Activity.mEmbeddedID, 其中Activity是指调用者所在Activity
- requestCode = -1;
- startFlags = 0;
- profilerInfo = null;
- outResult = null;
- config = null;
- options = null;
- ignoreTargetSecurity = false;
- userId = AMS.handleIncomingUser, 当调用者userId跟当前处于同一个userId,则直接返回该userId;当不相等时则根据调用者userId来决定是否需要将callingUserId转换为mCurrentUserId.
- iContainer = null;
- inTask = null;
再来看看这个方法的源码:
[-> ActivityStackSupervisor.java]
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 config, Bundle options, boolean ignoreTargetSecurity, int userId, IActivityContainer iContainer, TaskRecord inTask) {
...
boolean componentSpecified = intent.getComponent() != null;
//创建新的Intent对象，即便intent被修改也不受影响
intent = new Intent(intent);
//收集Intent所指向的Activity信息, 当存在多个可供选择的Activity,则直接向用户弹出resolveActivity [见2.7.1]
ActivityInfo aInfo = resolveActivity(intent, resolvedType, startFlags, profilerInfo, userId);
ActivityContainer container = (ActivityContainer)iContainer;
synchronized (mService) {
if (container != null && container.mParentActivity != null &&
container.mParentActivity.state != RESUMED) {
... //不进入该分支, container == nul
}
final int realCallingPid = Binder.getCallingPid();
final int realCallingUid = Binder.getCallingUid();
int callingPid;
if (callingUid >= 0) {
callingPid = -1;
} else if (caller == null) {
callingPid = realCallingPid;
callingUid = realCallingUid;
} else {
callingPid = callingUid = -1;
}
final ActivityStack stack;
if (container == null || container.mStack.isOnHomeDisplay()) {
stack = mFocusedStack; // 进入该分支
} else {
stack = container.mStack;
}
//此时mConfigWillChange = false
stack.mConfigWillChange = config != null && mService.mConfiguration.diff(config) != 0;
final long origId = Binder.clearCallingIdentity();
if (aInfo != null &&
(aInfo.applicationInfo.privateFlags
&ApplicationInfo.PRIVATE_FLAG_CANT_SAVE_STATE) != 0) {
// heavy-weight进程处理流程, 一般情况下不进入该分支
if (aInfo.processName.equals(aInfo.applicationInfo.packageName)) {
...
}
}
//[见流程2.8]
int res = startActivityLocked(caller, intent, resolvedType, aInfo,
voiceSession, voiceInteractor, resultTo, resultWho,
requestCode, callingPid, callingUid, callingPackage,
realCallingPid, realCallingUid, startFlags, options, ignoreTargetSecurity,
componentSpecified, null, container, inTask);
Binder.restoreCallingIdentity(origId);
if (stack.mConfigWillChange) {
... //不进入该分支
}
if (outResult != null) {
... //不进入该分支
}
return res;
}
}
该过程主要功能：通过resolveActivity来获取ActivityInfo信息, 然后再进入ASS.startActivityLocked().先来看看
2.7.1 ASS.resolveActivity
// startFlags = 0; profilerInfo = null; userId代表caller UserId
ActivityInfo resolveActivity(Intent intent, String resolvedType, int startFlags, ProfilerInfo profilerInfo, int userId) {
ActivityInfo aInfo;
ResolveInfo rInfo =
AppGlobals.getPackageManager().resolveIntent(
intent, resolvedType,
PackageManager.MATCH_DEFAULT_ONLY
| ActivityManagerService.STOCK_PM_FLAGS, userId);
aInfo = rInfo != null ? rInfo.activityInfo : null;
if (aInfo != null) {
intent.setComponent(new ComponentName(
aInfo.applicationInfo.packageName, aInfo.name));
if (!aInfo.processName.equals("system")) {
... //对于非system进程，根据flags来设置相应的debug信息
}
}
return aInfo;
}
ActivityManager类有如下4个flags用于调试：
- START_FLAG_DEBUG：用于调试debug app
- START_FLAG_OPENGL_TRACES：用于调试OpenGL tracing
- START_FLAG_NATIVE_DEBUGGING：用于调试native
- START_FLAG_TRACK_ALLOCATION: 用于调试allocation tracking
2.7.2 PKMS.resolveIntent
AppGlobals.getPackageManager()经过函数层层调用，获取的是ApplicationPackageManager对象。经过binder IPC调用，最终会调用PackageManagerService对象。故此时调用方法为PMS.resolveIntent().
[-> PackageManagerService.java]
public ResolveInfo resolveIntent(Intent intent, String resolvedType, int flags, int userId) {
if (!sUserManager.exists(userId)) return null;
enforceCrossUserPermission(Binder.getCallingUid(), userId, false, false, "resolve intent");
//[见流程2.7.3]
List<ResolveInfo> query = queryIntentActivities(intent, resolvedType, flags, userId);
//根据priority，preferred选择最佳的Activity
return chooseBestActivity(intent, resolvedType, flags, query, userId);
}
2.7.3 PMS.queryIntentActivities
public List<ResolveInfo> queryIntentActivities(Intent intent,
String resolvedType, int flags, int userId) {
...
ComponentName comp = intent.getComponent();
if (comp == null) {
if (intent.getSelector() != null) {
intent = intent.getSelector();
comp = intent.getComponent();
}
}
if (comp != null) {
final List<ResolveInfo> list = new ArrayList<ResolveInfo>(1);
//获取Activity信息
final ActivityInfo ai = getActivityInfo(comp, flags, userId);
if (ai != null) {
final ResolveInfo ri = new ResolveInfo();
ri.activityInfo = ai;
list.add(ri);
}
return list;
}
...
}
ASS.resolveActivity()方法的核心功能是找到相应的Activity组件，并保存到intent对象。
2.8 ASS.startActivityLocked
[-> ActivityStackSupervisor.java]
final int startActivityLocked(IApplicationThread caller,
Intent intent, String resolvedType, ActivityInfo aInfo,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode,
int callingPid, int callingUid, String callingPackage,
int realCallingPid, int realCallingUid, int startFlags, Bundle options,
boolean ignoreTargetSecurity, boolean componentSpecified, ActivityRecord[] outActivity,
ActivityContainer container, TaskRecord inTask) { int err = ActivityManager.START_SUCCESS;
//获取调用者的进程记录对象
ProcessRecord callerApp = null;
if (caller != null) {
callerApp = mService.getRecordForAppLocked(caller);
if (callerApp != null) {
callingPid = callerApp.pid;
callingUid = callerApp.info.uid;
} else {
err = ActivityManager.START_PERMISSION_DENIED;
}
}
final int userId = aInfo != null ? UserHandle.getUserId(aInfo.applicationInfo.uid) : 0;
ActivityRecord sourceRecord = null;
ActivityRecord resultRecord = null;
if (resultTo != null) {
//获取调用者所在的Activity
sourceRecord = isInAnyStackLocked(resultTo);
if (sourceRecord != null) {
if (requestCode >= 0 && !sourceRecord.finishing) {
... //requestCode = -1 则不进入
}
}
}
final int launchFlags = intent.getFlags();
if ((launchFlags & Intent.FLAG_ACTIVITY_FORWARD_RESULT) != 0 && sourceRecord != null) {
... // activity执行结果的返回由源Activity转换到新Activity, 不需要返回结果则不会进入该分支
}
if (err == ActivityManager.START_SUCCESS && intent.getComponent() == null) {
//从Intent中无法找到相应的Component
err = ActivityManager.START_INTENT_NOT_RESOLVED;
}
if (err == ActivityManager.START_SUCCESS && aInfo == null) {
//从Intent中无法找到相应的ActivityInfo
err = ActivityManager.START_INTENT_NOT_RESOLVED;
}
if (err == ActivityManager.START_SUCCESS
&& !isCurrentProfileLocked(userId)
&& (aInfo.flags & FLAG_SHOW_FOR_ALL_USERS) == 0) {
//尝试启动一个后台Activity, 但该Activity对当前用户不可见
err = ActivityManager.START_NOT_CURRENT_USER_ACTIVITY;
}
...
//执行后resultStack = null
final ActivityStack resultStack = resultRecord == null ? null : resultRecord.task.stack;
... //权限检查
// ActivityController不为空的情况，比如monkey测试过程
if (mService.mController != null) {
Intent watchIntent = intent.cloneFilter();
abort |= !mService.mController.activityStarting(watchIntent,
aInfo.applicationInfo.packageName);
}
if (abort) {
... //权限检查不满足,才进入该分支则直接返回；
return ActivityManager.START_SUCCESS;
}
// 创建Activity记录对象
ActivityRecord r = new ActivityRecord(mService, callerApp, callingUid, callingPackage,
intent, resolvedType, aInfo, mService.mConfiguration, resultRecord, resultWho,
requestCode, componentSpecified, voiceSession != null, this, container, options);
if (outActivity != null) {
outActivity[0] = r;
}
if (r.appTimeTracker == null && sourceRecord != null) {
r.appTimeTracker = sourceRecord.appTimeTracker;
}
// 将mFocusedStack赋予当前stack
final ActivityStack stack = mFocusedStack;
if (voiceSession == null && (stack.mResumedActivity == null
|| stack.mResumedActivity.info.applicationInfo.uid != callingUid)) {
// 前台stack还没有resume状态的Activity时, 则检查app切换是否允许 [见流程2.8.1]
if (!mService.checkAppSwitchAllowedLocked(callingPid, callingUid,
realCallingPid, realCallingUid, "Activity start")) {
PendingActivityLaunch pal =
new PendingActivityLaunch(r, sourceRecord, startFlags, stack);
// 当不允许切换,则把要启动的Activity添加到mPendingActivityLaunches对象, 并且直接返回.
mPendingActivityLaunches.add(pal);
ActivityOptions.abort(options);
return ActivityManager.START_SWITCHES_CANCELED;
}
}
if (mService.mDidAppSwitch) {
//从上次禁止app切换以来,这是第二次允许app切换,因此将允许切换时间设置为0,则表示可以任意切换app
mService.mAppSwitchesAllowedTime = 0;
} else {
mService.mDidAppSwitch = true;
}
//处理 pendind Activity的启动, 这些Activity是由于app switch禁用从而被hold的等待启动activity [见流程2.8.2]
doPendingActivityLaunchesLocked(false);
//[见流程2.9]
err = startActivityUncheckedLocked(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, true, options, inTask);
if (err < 0) {
notifyActivityDrawnForKeyguard();
}
return err;
}
其中有两个返回值代表启动Activity失败：
- START_INTENT_NOT_RESOLVED: 从Intent中无法找到相应的Component或者ActivityInfo
- START_NOT_CURRENT_USER_ACTIVITY：该Activity对当前用户不可见
2.8.1 AMS.checkAppSwitchAllowedLocked
boolean checkAppSwitchAllowedLocked(int sourcePid, int sourceUid, int callingPid, int callingUid, String name) {
if (mAppSwitchesAllowedTime < SystemClock.uptimeMillis()) {
return true;
}
int perm = checkComponentPermission(
android.Manifest.permission.STOP_APP_SWITCHES, sourcePid,
sourceUid, -1, true);
if (perm == PackageManager.PERMISSION_GRANTED) {
return true;
}
if (callingUid != -1 && callingUid != sourceUid) {
perm = checkComponentPermission(
android.Manifest.permission.STOP_APP_SWITCHES, callingPid,
callingUid, -1, true);
if (perm == PackageManager.PERMISSION_GRANTED) {
return true;
}
}
return false;
}
当mAppSwitchesAllowedTime时间小于当前时长,或者具有STOP_APP_SWITCHES的权限,则允许app发生切换操作.
其中mAppSwitchesAllowedTime, 在AMS.stopAppSwitches()的过程中会设置为:mAppSwitchesAllowedTime = SystemClock.uptimeMillis() + APP_SWITCH_DELAY_TIME. 禁止app切换的timeout时长为5s(APP_SWITCH_DELAY_TIME = 5s).
当发送5秒超时或者执行AMS.resumeAppSwitches()过程会将mAppSwitchesAllowedTime设置0, 都会开启允许app执行切换的操作.另外,禁止App切换的操作,对于同一个app是不受影响的,有兴趣可以进一步查看checkComponentPermission过程.
2.8.2 ASS.doPendingActivityLaunchesLocked
[-> ActivityStackSupervisor.java]
final void doPendingActivityLaunchesLocked(boolean doResume) {
while (!mPendingActivityLaunches.isEmpty()) {
PendingActivityLaunch pal = mPendingActivityLaunches.remove(0);
try {
//[见流程2.9]
startActivityUncheckedLocked(pal.r, pal.sourceRecord, null, null, pal.startFlags,
doResume && mPendingActivityLaunches.isEmpty(), null, null);
} catch (Exception e) {
...
}
}
}
mPendingActivityLaunches记录着所有将要启动的Activity, 是由于在startActivityLocked的过程时App切换功能被禁止, 也就是不运行切换Activity, 那么此时便会把相应的Activity加入到mPendingActivityLaunches队列. 该队列的成员在执行完doPendingActivityLaunchesLocked便会清空.
启动mPendingActivityLaunches中所有的Activity, 由于doResume = false, 那么这些activtity并不会进入resume状态,而是设置delayedResume = true, 会延迟resume.
2.9 ASS.startActivityUncheckedLocked
[-> ActivityStackSupervisor.java]
// sourceRecord是指调用者， r是指本次将要启动的Activity
final int startActivityUncheckedLocked(final ActivityRecord r, ActivityRecord sourceRecord, IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, int startFlags, boolean doResume, Bundle options, TaskRecord inTask) {
final Intent intent = r.intent;
final int callingUid = r.launchedFromUid;
if (inTask != null && !inTask.inRecents) {
inTask = null;
}
final boolean launchSingleTop = r.launchMode == ActivityInfo.LAUNCH_SINGLE_TOP;
final boolean launchSingleInstance = r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE;
final boolean launchSingleTask = r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK;
int launchFlags = intent.getFlags();
// 当intent和activity manifest存在冲突，则manifest优先
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_DOCUMENT) != 0 &&
(launchSingleInstance || launchSingleTask)) {
launchFlags &=
~(Intent.FLAG_ACTIVITY_NEW_DOCUMENT | Intent.FLAG_ACTIVITY_MULTIPLE_TASK);
} else {
...
}
final boolean launchTaskBehind = r.mLaunchTaskBehind
&& !launchSingleTask && !launchSingleInstance
&& (launchFlags & Intent.FLAG_ACTIVITY_NEW_DOCUMENT) != 0;
if (r.resultTo != null && (launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0
&& r.resultTo.task.stack != null) {
r.resultTo.task.stack.sendActivityResultLocked(-1,
r.resultTo, r.resultWho, r.requestCode,
Activity.RESULT_CANCELED, null);
r.resultTo = null;
}
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_DOCUMENT) != 0 && r.resultTo == null) {
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
}
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
if (launchTaskBehind
|| r.info.documentLaunchMode == ActivityInfo.DOCUMENT_LAUNCH_ALWAYS) {
launchFlags |= Intent.FLAG_ACTIVITY_MULTIPLE_TASK;
}
}
mUserLeaving = (launchFlags & Intent.FLAG_ACTIVITY_NO_USER_ACTION) == 0;
//当本次不需要resume，则设置为延迟resume的状态
if (!doResume) {
r.delayedResume = true;
}
ActivityRecord notTop =
(launchFlags & Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP) != 0 ? r : null;
if ((startFlags&ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
ActivityRecord checkedCaller = sourceRecord;
if (checkedCaller == null) {
checkedCaller = mFocusedStack.topRunningNonDelayedActivityLocked(notTop);
}
if (!checkedCaller.realActivity.equals(r.realActivity)) {
//调用者 与将要启动的Activity不相同时，进入该分支。
startFlags &= ~ActivityManager.START_FLAG_ONLY_IF_NEEDED;
}
}
boolean addingToTask = false;
TaskRecord reuseTask = null;
//当调用者不是来自activity，而是明确指定task的情况。
if (sourceRecord == null && inTask != null && inTask.stack != null) {
... //目前sourceRecord不为空，则不进入该分支
} else {
inTask = null;
}
if (inTask == null) {
if (sourceRecord == null) {
//调用者并不是Activity context,则强制创建新task
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) == 0 && inTask == null) {
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
}
} else if (sourceRecord.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//调用者activity带有single instance，则创建新task
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
} else if (launchSingleInstance || launchSingleTask) {
//目标activity带有single instance或者single task，则创建新task
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
}
}
ActivityInfo newTaskInfo = null;
Intent newTaskIntent = null;
ActivityStack sourceStack;
if (sourceRecord != null) {
if (sourceRecord.finishing) {
//调用者处于即将finish状态，则创建新task
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) == 0) {
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
newTaskInfo = sourceRecord.info;
newTaskIntent = sourceRecord.task.intent;
}
sourceRecord = null;
sourceStack = null;
} else {
//当调用者Activity不为空，且不处于finishing状态，则其所在栈赋于sourceStack
sourceStack = sourceRecord.task.stack;
}
} else {
sourceStack = null;
}
boolean movedHome = false;
ActivityStack targetStack;
intent.setFlags(launchFlags);
final boolean noAnimation = (launchFlags & Intent.FLAG_ACTIVITY_NO_ANIMATION) != 0;
if (((launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0 &&
(launchFlags & Intent.FLAG_ACTIVITY_MULTIPLE_TASK) == 0)
|| launchSingleInstance || launchSingleTask) {
if (inTask == null && r.resultTo == null) {
//从mActivityDisplays开始查询是否有相应ActivityRecord
ActivityRecord intentActivity = !launchSingleInstance ?
findTaskLocked(r) : findActivityLocked(intent, r.info);
if (intentActivity != null) {
if (isLockTaskModeViolation(intentActivity.task,
(launchFlags & (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK))
== (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK))) {
return ActivityManager.START_RETURN_LOCK_TASK_MODE_VIOLATION;
}
if (r.task == null) {
r.task = intentActivity.task;
}
if (intentActivity.task.intent == null) {
intentActivity.task.setIntent(r);
}
targetStack = intentActivity.task.stack;
targetStack.mLastPausedActivity = null;
final ActivityStack focusStack = getFocusedStack();
ActivityRecord curTop = (focusStack == null)
? null : focusStack.topRunningNonDelayedActivityLocked(notTop);
boolean movedToFront = false;
if (curTop != null && (curTop.task != intentActivity.task ||
curTop.task != focusStack.topTask())) {
r.intent.addFlags(Intent.FLAG_ACTIVITY_BROUGHT_TO_FRONT);
if (sourceRecord == null || (sourceStack.topActivity() != null &&
sourceStack.topActivity().task == sourceRecord.task)) {
if (launchTaskBehind && sourceRecord != null) {
intentActivity.setTaskToAffiliateWith(sourceRecord.task);
}
movedHome = true;
//将该task移至前台
targetStack.moveTaskToFrontLocked(intentActivity.task, noAnimation,
options, r.appTimeTracker, "bringingFoundTaskToFront");
movedToFront = true;
if ((launchFlags &
(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_TASK_ON_HOME))
== (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_TASK_ON_HOME)) {
//将toReturnTo设置为home
intentActivity.task.setTaskToReturnTo(HOME_ACTIVITY_TYPE);
}
options = null;
}
}
if (!movedToFront) {
targetStack.moveToFront("intentActivityFound");
}
if ((launchFlags&Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) != 0) {
//重置目标task
intentActivity = targetStack.resetTaskIfNeededLocked(intentActivity, r);
}
if ((startFlags & ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
if (doResume) {
resumeTopActivitiesLocked(targetStack, null, options);
//当没有启动至前台，则通知Keyguard
if (!movedToFront) {
notifyActivityDrawnForKeyguard();
}
} else {
ActivityOptions.abort(options);
}
return ActivityManager.START_RETURN_INTENT_TO_CALLER;
}
if ((launchFlags & (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK))
== (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK)) {
reuseTask = intentActivity.task;
//移除所有跟已存在的task有关联的activity
reuseTask.performClearTaskLocked();
reuseTask.setIntent(r);
} else if ((launchFlags & FLAG_ACTIVITY_CLEAR_TOP) != 0
|| launchSingleInstance || launchSingleTask) {
ActivityRecord top =
intentActivity.task.performClearTaskLocked(r, launchFlags);
if (top != null) {
if (top.frontOfTask) {
top.task.setIntent(r);
}
//触发onNewIntent()
top.deliverNewIntentLocked(callingUid, r.intent, r.launchedFromPackage);
} else {
sourceRecord = intentActivity;
TaskRecord task = sourceRecord.task;
if (task != null && task.stack == null) {
targetStack = computeStackFocus(sourceRecord, false /* newTask */);
targetStack.addTask(
task, !launchTaskBehind /* toTop */, false /* moving */);
}
}
} else if (r.realActivity.equals(intentActivity.task.realActivity)) {
if (((launchFlags&Intent.FLAG_ACTIVITY_SINGLE_TOP) != 0 || launchSingleTop)
&& intentActivity.realActivity.equals(r.realActivity)) {
if (intentActivity.frontOfTask) {
intentActivity.task.setIntent(r);
}
//触发onNewIntent()
intentActivity.deliverNewIntentLocked(callingUid, r.intent,
r.launchedFromPackage);
} else if (!r.intent.filterEquals(intentActivity.task.intent)) {
addingToTask = true;
sourceRecord = intentActivity;
}
} else if ((launchFlags&Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) == 0) {
addingToTask = true;
sourceRecord = intentActivity;
} else if (!intentActivity.task.rootWasReset) {
intentActivity.task.setIntent(r);
}
if (!addingToTask && reuseTask == null) {
if (doResume) {
targetStack.resumeTopActivityLocked(null, options);
if (!movedToFront) {
notifyActivityDrawnForKeyguard();
}
} else {
ActivityOptions.abort(options);
}
return ActivityManager.START_TASK_TO_FRONT;
}
}
}
}
if (r.packageName != null) {
//当启动的activity跟前台显示是同一个的情况
ActivityStack topStack = mFocusedStack;
ActivityRecord top = topStack.topRunningNonDelayedActivityLocked(notTop);
if (top != null && r.resultTo == null) {
if (top.realActivity.equals(r.realActivity) && top.userId == r.userId) {
if (top.app != null && top.app.thread != null) {
if ((launchFlags & Intent.FLAG_ACTIVITY_SINGLE_TOP) != 0
|| launchSingleTop || launchSingleTask) {
topStack.mLastPausedActivity = null;
if (doResume) {
resumeTopActivitiesLocked();
}
ActivityOptions.abort(options);
if ((startFlags&ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
}
//触发onNewIntent()
top.deliverNewIntentLocked(callingUid, r.intent, r.launchedFromPackage);
return ActivityManager.START_DELIVERED_TO_TOP;
}
}
}
}
} else {
if (r.resultTo != null && r.resultTo.task.stack != null) {
r.resultTo.task.stack.sendActivityResultLocked(-1, r.resultTo, r.resultWho,
r.requestCode, Activity.RESULT_CANCELED, null);
}
ActivityOptions.abort(options);
return ActivityManager.START_CLASS_NOT_FOUND;
}
boolean newTask = false;
boolean keepCurTransition = false;
TaskRecord taskToAffiliate = launchTaskBehind && sourceRecord != null ?
sourceRecord.task : null;
if (r.resultTo == null && inTask == null && !addingToTask
&& (launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
newTask = true;
targetStack = computeStackFocus(r, newTask);
targetStack.moveToFront("startingNewTask");
if (reuseTask == null) {
r.setTask(targetStack.createTaskRecord(getNextTaskId(),
newTaskInfo != null ? newTaskInfo : r.info,
newTaskIntent != null ? newTaskIntent : intent,
voiceSession, voiceInteractor, !launchTaskBehind /* toTop */),
taskToAffiliate);
} else {
r.setTask(reuseTask, taskToAffiliate);
}
if (isLockTaskModeViolation(r.task)) {
return ActivityManager.START_RETURN_LOCK_TASK_MODE_VIOLATION;
}
if (!movedHome) {
if ((launchFlags &
(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_TASK_ON_HOME))
== (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_TASK_ON_HOME)) {
r.task.setTaskToReturnTo(HOME_ACTIVITY_TYPE);
}
}
} else if (sourceRecord != null) {
final TaskRecord sourceTask = sourceRecord.task;
if (isLockTaskModeViolation(sourceTask)) {
return ActivityManager.START_RETURN_LOCK_TASK_MODE_VIOLATION;
}
targetStack = sourceTask.stack;
targetStack.moveToFront("sourceStackToFront");
final TaskRecord topTask = targetStack.topTask();
if (topTask != sourceTask) {
targetStack.moveTaskToFrontLocked(sourceTask, noAnimation, options,
r.appTimeTracker, "sourceTaskToFront");
}
if (!addingToTask && (launchFlags&Intent.FLAG_ACTIVITY_CLEAR_TOP) != 0) {
ActivityRecord top = sourceTask.performClearTaskLocked(r, launchFlags);
keepCurTransition =