本系列博客将详细阐述Activity的启动流程。
深入理解Activity启动流程(一)–Activity启动的概要流程
深入理解Activity启动流程(二)–Activity启动相关类的类图
深入理解Activity启动流程(三)–Activity启动的详细流程1
深入理解Activity启动流程(三)–Activity启动的详细流程2
前面两篇博客介绍了Activity的详细启动流程，提到ActivityStack类的startActivityUncheckedLocked方法负责调度ActivityRecord和Task，并且调度算法非常复杂，需结合实际场景分析调度算法。本篇博客将介绍startActivityUncheckedLocked方法的具体实现，本结合实际场景分析调度算法。
startActivityUncheckedLocked方法的具体实现
final int startActivityUncheckedLocked(ActivityRecord r,
ActivityRecord sourceRecord, int startFlags, boolean doResume,
Bundle options) {
//...
//如果从Launcher程序启动应用，launchFlags为
//FLAG_ACTIVITY_NEW_TASK|FLAG_ACTIVITY_RESET_TASK_IF_NEEDED
//否则一般情况下launcheFlags为0，除非启动Activity时设置了特殊的flag
int launchFlags = intent.getFlags();
//启动Activity时默认不会设置FLAG_ACTIVITY_PREVIOUS_IS_TOP
//故此notTop默认情况下会是null
ActivityRecord notTop = (launchFlags&Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP)
!= 0 ? r : null;
//默认情况下startFlags不会设置START_FLAG_ONLY_IF_NEEDED
// If the onlyIfNeeded flag is set, then we can do this if the activity
// being launched is the same as the one making the call... or, as
// a special case, if we do not know the caller then we count the
// current top activity as the caller.
if ((startFlags&ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
//...默认情况下这里的代码不会执行
}
//根据被启动的Activity和sourceRecord设置标志
//launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK
//如果从通知栏启动应用 sourceRecord == null
if (sourceRecord == null) {
// This activity is not being started from another... in this
// case we -always- start a new task.
if ((launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) == 0) {
Slog.w(TAG, "startActivity called from non-Activity context;"
+"forcing Intent.FLAG_ACTIVITY_NEW_TASK for: "
+ intent);
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
}
} else if (sourceRecord.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
// The original activity who is starting us is running as a single
// instance... this new activity it is starting must go on its
// own task.
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
} else if (r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK) {
// The activity being started is a single instance... it always
// gets launched into its own task.
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
}
//一般情况下r.resultTo 不为null，它是启动该Activity的Activity，
//如果从通知栏启动Activity 则r.result为null
if (r.resultTo != null && (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
//...
r.resultTo = null;
}
//addingToTask 如果为true表示正在添加至某个task，
// 后续需要将r添加至sourceRecord所在的task
boolean addingToTask = false;
//movedHome表示是否移动home task
boolean movedHome = false;
//reuseTask 如果不为null,则表示已存在task，会重用这个task，
// 但是这个Task里的所有Activity会被清除掉,
// 需要将r加入这个task
TaskRecord reuseTask = null;
if (((launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0 &&
(launchFlags&Intent.FLAG_ACTIVITY_MULTIPLE_TASK) == 0)
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//从通知栏启动时r.resultTo == null
//如果launchFlags设置了FLAG_ACTIVITY_NEW_TASK,r.resultTo也会为null
if (r.resultTo == null) {
//查找ActivityRecord栈，看要启动的activity是否已有相关task，
//如果已经有相关task，则不需要创建新的task，可以使用已有的task
//如果要启动的activity的启动模式是LAUNCH_SINGLE_INSTANCE，
//则使用快速查找方法findTaskLocked，否则使用慢速查找方法findActivityLocked
//因为如果启动模式是LAUNCH_SINGLE_INSTANCE,则这个activity只会在一个单独的Task里
//故此查找时，可以以task为单位进行查找和比较，这样比较快
//查找得到的结果taskTop是相关task的栈顶的ActivityRecord
// See if there is a task to bring to the front. If this is
// a SINGLE_INSTANCE activity, there can be one and only one
// instance of it in the history, and it is always in its own
// unique task, so we do a special search.
ActivityRecord taskTop = r.launchMode != ActivityInfo.LAUNCH_SINGLE_INSTANCE
? findTaskLocked(intent, r.info)
: findActivityLocked(intent, r.info);
//找到了相关task
if (taskTop != null) {
//重设task的intent
if (taskTop.task.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.
taskTop.task.setIntent(intent, r.info);
}
//如果目标task不在栈顶，
//则先将Home task移动到栈顶(实际上只有当启动Activity设置的Flag同时设置了
//FLAG_ACTIVITY_TASK_ON_HOME和FLAG_ACTIVITY_NEW_TASK才会移动home task，
//否则不会移动home task)，
//然后再将目标task移动到栈顶
// If the target task is not in the front, then we need
// to bring it to the front... except... well, with
// SINGLE_TASK_LAUNCH it's not entirely clear. We'd like
// to have the same behavior as if a new instance was
// being started, which means not bringing it to the front
// if the caller is not itself in the front.
ActivityRecord curTop = topRunningNonDelayedActivityLocked(notTop);
if (curTop != null && curTop.task != taskTop.task) {
r.intent.addFlags(Intent.FLAG_ACTIVITY_BROUGHT_TO_FRONT);
boolean callerAtFront = sourceRecord == null
|| curTop.task == sourceRecord.task;
if (callerAtFront) {
// We really do want to push this one into the
// user's face, right now.
movedHome = true;
moveHomeToFrontFromLaunchLocked(launchFlags);
moveTaskToFrontLocked(taskTop.task, r, options);
options = null;
}
}
//如果launchFlags设置了FLAG_ACTIVITY_RESET_TASK_IF_NEEDED，则会重置task
//从Launcher应用程序启动应用会设置FLAG_ACTIVITY_RESET_TASK_IF_NEEDED
// If the caller has requested that the target task be
// reset, then do so.
if ((launchFlags&Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) != 0) {
taskTop = resetTaskIfNeededLocked(taskTop, r);
}
//... 一般情况下startFlags 不会设置 START_FLAG_ONLY_IF_NEEDED
if ((startFlags&ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
//...
}
// ==================================
//默认情况下不会设置 Intent.FLAG_ACTIVITY_CLEAR_TASK
if ((launchFlags &
(Intent.FLAG_ACTIVITY_NEW_TASK|Intent.FLAG_ACTIVITY_CLEAR_TASK))
== (Intent.FLAG_ACTIVITY_NEW_TASK|Intent.FLAG_ACTIVITY_CLEAR_TASK)) {
// The caller has requested to completely replace any
// existing task with its new activity. Well that should
// not be too hard...
reuseTask = taskTop.task;
performClearTaskLocked(taskTop.task.taskId);
reuseTask.setIntent(r.intent, r.info);
} else if ((launchFlags&Intent.FLAG_ACTIVITY_CLEAR_TOP) != 0
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//默认情况下launchFlags不会设置FLAG_ACTIVITY_CLEAR_TOP
//但是如果被启动的activity的启动模式是singleTask或者singleInstance，
//也会进入该分支
// 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.
//清除r所在的task 在r之上的所有activity,
//该task里r和在r下的activity不会被清除
ActivityRecord top = performClearTaskLocked(
taskTop.task.taskId, r, launchFlags);
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.task.setIntent(r.intent, r.info);
}
logStartActivity(EventLogTags.AM_NEW_INTENT, r, top.task);
top.deliverNewIntentLocked(callingUid, r.intent);
} else {
// 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.
addingToTask = true;
// Now pretend like this activity is being started
// by the top of its task, so it is put in the
// right place.
sourceRecord = taskTop;
}
} else if (r.realActivity.equals(taskTop.task.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.
if (((launchFlags&Intent.FLAG_ACTIVITY_SINGLE_TOP) != 0
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TOP)
&& taskTop.realActivity.equals(r.realActivity)) {
logStartActivity(EventLogTags.AM_NEW_INTENT, r, taskTop.task);
if (taskTop.frontOfTask) {
taskTop.task.setIntent(r.intent, r.info);
}
taskTop.deliverNewIntentLocked(callingUid, r.intent);
} else if (!r.intent.filterEquals(taskTop.task.intent)) {
// 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.
addingToTask = true;
sourceRecord = taskTop;
}
} else if ((launchFlags&Intent.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.
addingToTask = true;
sourceRecord = taskTop;
} else if (!taskTop.task.rootWasReset) {
//进入该分支的情况比较少
// In this case we are launching in to 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.
taskTop.task.setIntent(r.intent, r.info);
}
// ================================== end
//如果没有正在添加至某个Task， 并且不用加入一个已清除所有Activity的Task
//此时只需要显示栈顶Activity即可
if (!addingToTask && reuseTask == 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.
if (doResume) {
resumeTopActivityLocked(null, options);
} else {
ActivityOptions.abort(options);
}
return ActivityManager.START_TASK_TO_FRONT;
}
}
}
}
//...
if (r.packageName != null) {
// 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.
ActivityRecord top = 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
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TOP
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK) {
//singleTop启动模式或者singleTask启动模式，
//并且task栈顶的activity是要启动的activity，则先显示Activity
//然后调用该Activity的onNewIntent方法
logStartActivity(EventLogTags.AM_NEW_INTENT, top, top.task);
// For paranoia, make sure we have correctly
// resumed the top activity.
//先显示Activity
if (doResume) {
resumeTopActivityLocked(null);
}
ActivityOptions.abort(options);
if ((startFlags&ActivityManager.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 ActivityManager.START_RETURN_INTENT_TO_CALLER;
}
//然后调用已显示activity的onNewIntent方法
top.deliverNewIntentLocked(callingUid, r.intent);
return ActivityManager.START_DELIVERED_TO_TOP;
}
}
}
}
} else {
if (r.resultTo != null) {
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;
// Should this be considered a new task?
if (r.resultTo == null && !addingToTask
&& (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
if (reuseTask == null) {
//创建新的task
// todo: should do better management of integers.
mService.mCurTask++;
if (mService.mCurTask <= 0) {
mService.mCurTask = 1;
}
r.setTask(new TaskRecord(mService.mCurTask, r.info, intent), null, true);
if (DEBUG_TASKS) Slog.v(TAG, "Starting new activity " + r
+ " in new task " + r.task);
} else {
//重复利用先前的task，该task里的所有acitivity已经被清空
r.setTask(reuseTask, reuseTask, true);
}
newTask = true;
if (!movedHome) {
moveHomeToFrontFromLaunchLocked(launchFlags);
}
} else if (sourceRecord != null) {
if (!addingToTask &&
(launchFlags&Intent.FLAG_ACTIVITY_CLEAR_TOP) != 0) {
// In this case, we are adding the activity to an existing
// task, but the caller has asked to clear that task if the
// activity is already running.
//清除r所在task在r之上的所有task，如果r不在task里，则返回的top为null
ActivityRecord top = performClearTaskLocked(
sourceRecord.task.taskId, r, launchFlags);
keepCurTransition = true;
if (top != null) {
logStartActivity(EventLogTags.AM_NEW_INTENT, r, top.task);
//先调用onNewIntent方法 然后再显示
top.deliverNewIntentLocked(callingUid, r.intent);
// For paranoia, make sure we have correctly
// resumed the top activity.
if (doResume) {
resumeTopActivityLocked(null);
}
ActivityOptions.abort(options);
return ActivityManager.START_DELIVERED_TO_TOP;
}
} else if (!addingToTask &&
(launchFlags&Intent.FLAG_ACTIVITY_REORDER_TO_FRONT) != 0) {
//将栈里已有的activity移到栈顶
// In this case, we are launching an activity in our own task
// that may already be running somewhere in the history, and
// we want to shuffle it to the front of the stack if so.
int where = findActivityInHistoryLocked(r, sourceRecord.task.taskId);
if (where >= 0) {
ActivityRecord top = moveActivityToFrontLocked(where);
logStartActivity(EventLogTags.AM_NEW_INTENT, r, top.task);
top.updateOptionsLocked(options);
top.deliverNewIntentLocked(callingUid, r.intent);
if (doResume) {
resumeTopActivityLocked(null);
}
return ActivityManager.START_DELIVERED_TO_TOP;
}
}
// An existing activity is starting this new activity, so we want
// to keep the new one in the same task as the one that is starting
// it.
//同一个应用程序里的Activity A和Activity B，A可跳转至B，没有设置taskAffinity
//B的启动模式为singleTask，从A跳转至B时，B和A会在同一个task里
//该情况下会执行到这里的代码，将B的task设置为和A一样的task
r.setTask(sourceRecord.task, sourceRecord.thumbHolder, false);
if (DEBUG_TASKS) Slog.v(TAG, "Starting new activity " + r
+ " in existing task " + r.task);
} 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.
final int N = mHistory.size();
ActivityRecord prev =
N > 0 ? mHistory.get(N-1) : null;
r.setTask(prev != null
? prev.task
: new TaskRecord(mService.mCurTask, r.info, intent), null, true);
if (DEBUG_TASKS) Slog.v(TAG, "Starting new activity " + r
+ " in new guessed " + r.task);
}
mService.grantUriPermissionFromIntentLocked(callingUid, r.packageName,
intent, r.getUriPermissionsLocked());
if (newTask) {
EventLog.writeEvent(EventLogTags.AM_CREATE_TASK, r.userId, r.task.taskId);
}
logStartActivity(EventLogTags.AM_CREATE_ACTIVITY, r, r.task);
startActivityLocked(r, newTask, doResume, keepCurTransition, options);
return ActivityManager.START_SUCCESS;
}
实际场景分析
实际场景1:
应用内有两个Activity,A和B,A为第应用入口Activity，从A可跳转至B，A和B的启动模式都为standard
1)从Launcher程序第1次启动应用时的任务调度情况:
任务调度时会创建新task并将新的ActivityRecord加入这个新的task
2)然后跳转至应用内Activity时的任务调度情况:
任务调度时会将新的ActivityRecord加入已有的task
3)然后按Home键，再打开应用程序时的调度情况:
任务调度时会先找到已有的相关task，并显示栈顶的Activity
1)从Launcher程序第1次启动应用时
会创建新task并将新的ActivityRecord加入这个新的task，任务调度执行如下所示:
final int startActivityUncheckedLocked(ActivityRecord r,
ActivityRecord sourceRecord, int startFlags, boolean doResume,
Bundle options) {
//...
//launchFlags为FLAG_ACTIVITY_NEW_TASK|FLAG_ACTIVITY_RESET_TASK_IF_NEEDED
int launchFlags = intent.getFlags();
//...
//没设置FLAG_ACTIVITY_PREVIOUS_IS_TOP，故此notTop为null
ActivityRecord notTop = (launchFlags&Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP)
!= 0 ? r : null;
//startFlags未设置ActivityManager.START_FLAG_ONLY_IF_NEEDED
//...
//sourceRecord为Launcher应用的Activity launcher应用activity的启动模式为singleTask
// 故此下面的3个条件分支的内容都不会执行
if (sourceRecord == null) {
//...
} else if (sourceRecord.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//...
} else if (r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK) {
//...
}
//...
//r.resultTo不为null， launchFlags设置了FLAG_ACTIVITY_NEW_TASK，需要将r.resultTo置为null
if (r.resultTo != null && (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
//...
r.resultTo = null;
}
boolean addingToTask = false;
boolean movedHome = false;
TaskRecord reuseTask = null;
//因为launchFlags为FLAG_ACTIVITY_NEW_TASK|FLAG_ACTIVITY_RESET_TASK_IF_NEEDED
//故此下面的条件会满足， 也就是说只要从Launcher程序启动应用，下面这个条件肯定会满足
if (((launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0 &&
(launchFlags&Intent.FLAG_ACTIVITY_MULTIPLE_TASK) == 0)
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//...
if (r.resultTo == null) {
//因为应用被第一次启动，故此找不到相关task，taskTop则为null
ActivityRecord taskTop = r.launchMode != ActivityInfo.LAUNCH_SINGLE_INSTANCE
? findTaskLocked(intent, r.info)
: findActivityLocked(intent, r.info);
if (taskTop != null) {
//... 这里面的内容不会执行
}
}
}
//...
//r.packageName != null
if (r.packageName != null) {
//如果被启动的Activity正好是栈顶的Activity，
//并且被启动的Activity启动模式是singleTop或者singleTask，
//则不用将新的ActivityRecord加入到栈里
//top Activity为Launcher应用的Activity
ActivityRecord top = topRunningNonDelayedActivityLocked(notTop);
if (top != null && r.resultTo == null) {
//top.realActivity.equals(r.realActivity)不满足
if (top.realActivity.equals(r.realActivity) && top.userId == r.userId) {
//... 这里的代码不会被执行
}
}
} else {
//...
}
boolean newTask = false;
boolean keepCurTransition = false;
// 此时 r.resultTo为null addingToTask为false launchFlags设置了FLAG_ACTIVITY_NEW_TASK
if (r.resultTo == null && !addingToTask
&& (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
if (reuseTask == null) {
// todo: should do better management of integers.
mService.mCurTask++;
if (mService.mCurTask <= 0) {
mService.mCurTask = 1;
}
//创建新task
r.setTask(new TaskRecord(mService.mCurTask, r.info, intent), null, true);
if (DEBUG_TASKS) Slog.v(TAG, "Starting new activity " + r
+ " in new task " + r.task);
} else {
//...这里的代码会执行
}
newTask = true;
if (!movedHome) {
moveHomeToFrontFromLaunchLocked(launchFlags);
}
} else if (sourceRecord != null) {
//... 这里的代码不会被执行
} else {
//...这里的代码不会被执行
}
//...
startActivityLocked(r, newTask, doResume, keepCurTransition, options);
return ActivityManager.START_SUCCESS;
}
2)跳转至应用内Activity时
会将新的ActivityRecord加入已有的task，任务调度执行如下所示:
final int startActivityUncheckedLocked(ActivityRecord r,
ActivityRecord sourceRecord, int startFlags, boolean doResume,
Bundle options) {
//此时launchFlags为0
int launchFlags = intent.getFlags();
//notTop为null
ActivityRecord notTop = (launchFlags&Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP)
!= 0 ? r : null;
//startFlags未设置ActivityManager.START_FLAG_ONLY_IF_NEEDED
//...
if (sourceRecord == null) {
//...这里的代码不会被执行
} else if (sourceRecord.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//...这里的代码不会被执行
} else if (r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK) {
//...这里的代码不会被执行
}
//r.resultTo != null 但是launchFlags未设置FLAG_ACTIVITY_NEW_TASK
if (r.resultTo != null && (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
//... 这里的代码不执行
}
boolean addingToTask = false;
boolean movedHome = false;
TaskRecord reuseTask = null;
//launchFlags为0 r的启动模式为standard 故此下面的逻辑都不会执行
if (((launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0 &&
(launchFlags&Intent.FLAG_ACTIVITY_MULTIPLE_TASK) == 0)
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//... 这里的代码不执行
}
//...
if (r.packageName != null) {
//top 是ActivityA 的ActivityRecord，
//但是被启动的Activity和top不是同一个Activity
ActivityRecord top = topRunningNonDelayedActivityLocked(notTop);
if (top != null && r.resultTo == null) {
if (top.realActivity.equals(r.realActivity) && top.userId == r.userId) {
//...这里的代码不执行
}
}
} else {
//...这里的代码不执行
}
boolean newTask = false;
boolean keepCurTransition = false;
//此时 r.resultTo !=null sourceRecord != null addingToTask=false
if (r.resultTo == null && !addingToTask
&& (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
//...这里的代码不执行
} else if (sourceRecord != null) {
if (!addingToTask &&
(launchFlags&Intent.FLAG_ACTIVITY_CLEAR_TOP) != 0) {
//... 这里的代码不执行
} else if (!addingToTask &&
(launchFlags&Intent.FLAG_ACTIVITY_REORDER_TO_FRONT) != 0) {
//... 这里的代码不执行
}
//添加到现有的task
r.setTask(sourceRecord.task, sourceRecord.thumbHolder, false);
//...
} else {
//... 这里的代码不执行
}
//...
return ActivityManager.START_SUCCESS;
}
3)然后按Home键，再打开应用程序
此时会先找到已有的相关task，并显示栈顶的Activity，任务调度执行如下所示:
final int startActivityUncheckedLocked(ActivityRecord r,
ActivityRecord sourceRecord, int startFlags, boolean doResume,
Bundle options) {
//...
//launchFlags为FLAG_ACTIVITY_NEW_TASK|FLAG_ACTIVITY_RESET_TASK_IF_NEEDED
int launchFlags = intent.getFlags();
//notTop为null
ActivityRecord notTop = (launchFlags&Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP)
!= 0 ? r : null;
//startFlags未设置ActivityManager.START_FLAG_ONLY_IF_NEEDED
//...
if (sourceRecord == null) {
//...这里的代码不会被执行
} else if (sourceRecord.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//...这里的代码不会被执行
} else if (r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK) {
//...这里的代码不会被执行
}
//此时 r.resultTo != null launchFlags设置了FLAG_ACTIVITY_NEW_TASK
if (r.resultTo != null && (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
//...
r.resultTo = null;
}
boolean addingToTask = false;
boolean movedHome = false;
TaskRecord reuseTask = null;
//此时launchFlags设置了FLAG_ACTIVITY_NEW_TASK|FLAG_ACTIVITY_RESET_TASK_IF_NEEDED
if (((launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0 &&
(launchFlags&Intent.FLAG_ACTIVITY_MULTIPLE_TASK) == 0)
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//此时 r.resultTo == null
if (r.resultTo == null) {
//此时已有相关task，并且task 栈的栈顶是Activity B的ActivityRecord
//故此taskTop为Activity B的ActivityRecord
ActivityRecord taskTop = r.launchMode != ActivityInfo.LAUNCH_SINGLE_INSTANCE
? findTaskLocked(intent, r.info)
: findActivityLocked(intent, r.info);
if (taskTop != null) {
//...
// 此时curTop是Launcher应用的Activity的ActivityRecord
ActivityRecord curTop = topRunningNonDelayedActivityLocked(notTop);
if (curTop != null && curTop.task != taskTop.task) {
r.intent.addFlags(Intent.FLAG_ACTIVITY_BROUGHT_TO_FRONT);
//此时Launcher应用的task在栈顶，故此callerAtFront为true，
//此时会把被启动的应用的task移至栈顶
boolean callerAtFront = sourceRecord == null
|| curTop.task == sourceRecord.task;
if (callerAtFront) {
// We really do want to push this one into the
// user's face, right now.
movedHome = true;
moveHomeToFrontFromLaunchLocked(launchFlags);
moveTaskToFrontLocked(taskTop.task, r, options);
options = null;
}
}
//此时launchFlags设置了FLAG_ACTIVITY_NEW_TASK|FLAG_ACTIVITY_RESET_TASK_IF_NEEDED
//此时需要重置task 重置完后 taskTop为ActivityB的ActivityRecord
if ((launchFlags&Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) != 0) {
taskTop = resetTaskIfNeededLocked(taskTop, r);
}
//startFlags为0
if ((startFlags&ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
//... 这些代码都不会被执行
}
//根据launchFlags和被启动的activity的信息 设置resueTask addingTask变量的值
//没设置 Intent.FLAG_ACTIVITY_CLEAR_TASK
if ((launchFlags &
(Intent.FLAG_ACTIVITY_NEW_TASK|Intent.FLAG_ACTIVITY_CLEAR_TASK))
== (Intent.FLAG_ACTIVITY_NEW_TASK|Intent.FLAG_ACTIVITY_CLEAR_TASK)) {
//... 这些代码都不会被执行
} else if ((launchFlags&Intent.FLAG_ACTIVITY_CLEAR_TOP) != 0
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//... 这些代码都不会被执行
} else if (r.realActivity.equals(taskTop.task.realActivity)) {
//... 这些代码都不会被执行
} else if ((launchFlags&Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) == 0) {
//因为从Launcher程序启动时launchFlags设置了FLAG_ACTIVITY_RESET_TASK_IF_NEEDED
//所以不会进入该分支
//... 这些代码都不会被执行
} else if (!taskTop.task.rootWasReset) {
//... 这些代码都不会被执行
}
//此时addingToTask为false，reuseTask为null，故此显示栈顶Actvity即可
if (!addingToTask && reuseTask == 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.
if (doResume) {
resumeTopActivityLocked(null, options);
} else {
ActivityOptions.abort(options);
}
return ActivityManager.START_TASK_TO_FRONT;
}
}
}
}
//... 以下代码都不会被执行
}
实际场景2:
应用内有两个Activity,A和B,A为第应用入口Activity，从A可跳转至B，A的启动模式都为standard，B的启动模式为singleTop
此时已从Launchenr程序打开应用，启动了Actvity A,再从A跳转至B，此时的任务调度情况:
此时不会创建新的Task，而是将B的ActivityRecord加入到A所在的task里
任务调度执行如下所示:
final int startActivityUncheckedLocked(ActivityRecord r,
ActivityRecord sourceRecord, int startFlags, boolean doResume,
Bundle options) {
//...
//此时launcheFlags为0
int launchFlags = intent.getFlags();
//notTop为null
ActivityRecord notTop = (launchFlags&Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP)
!= 0 ? r : null;
//默认情况下startFlags不会设置START_FLAG_ONLY_IF_NEEDED
if ((startFlags&ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
//...这里的代码不会执行
}
//r.launchMode = ActivityInfo.LAUNCH_SINGLE_TASK
if (sourceRecord == null) {
//这里的代码不会执行
} else if (sourceRecord.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//这里的代码不会执行
} else if (r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK) {
launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
}
//此时r.resultTo!=null launchFlags设置了Intent.FLAG_ACTIVITY_NEW_TASK
if (r.resultTo != null && (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
//...
r.resultTo = null;
}
//addingToTask如果为true表示正在添加至某个task，后续需要将r添加至sourceRecord所在的task
boolean addingToTask = false;
//movedHome表示是否移动home task
boolean movedHome = false;
TaskRecord reuseTask = null;
if (((launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0 &&
(launchFlags&Intent.FLAG_ACTIVITY_MULTIPLE_TASK) == 0)
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
//此时 r.resultTo = null
if (r.resultTo == null) {
//此时找到的taskTop是Activity A的ActivityRecord，
//因为Actvity B和A的ActivityRecord所在的Task是相关的
ActivityRecord taskTop = r.launchMode != ActivityInfo.LAUNCH_SINGLE_INSTANCE
? findTaskLocked(intent, r.info)
: findActivityLocked(intent, r.info);
//找到了相关task
if (taskTop != null) {
//重设task的intent
if (taskTop.task.intent == null) {
//...
}
//此时找到的task已在栈顶
ActivityRecord curTop = topRunningNonDelayedActivityLocked(notTop);
if (curTop != null && curTop.task != taskTop.task) {
//... 这里的代码不会执行
}
//launchFlags为0
if ((launchFlags&Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) != 0) {
taskTop = resetTaskIfNeededLocked(taskTop, r);
}
//... 一般情况下startFlags 不会设置 START_FLAG_ONLY_IF_NEEDED
if ((startFlags&ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {
//...
}
// ==================== begin
// launchFlags此时为0
if ((launchFlags &
(Intent.FLAG_ACTIVITY_NEW_TASK|Intent.FLAG_ACTIVITY_CLEAR_TASK))
== (Intent.FLAG_ACTIVITY_NEW_TASK|Intent.FLAG_ACTIVITY_CLEAR_TASK)) {
//...这里的代码不执行
} else if ((launchFlags&Intent.FLAG_ACTIVITY_CLEAR_TOP) != 0
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK
|| r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
// r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK
// 故此会进入该分支
//因为B还从未启动，故此得到的top为null
ActivityRecord top = performClearTaskLocked(
taskTop.task.taskId, r, launchFlags);
if (top != null) {
//...这里的代码不执行
} else {
addingToTask = true;
sourceRecord = taskTop;
}
} else if (r.realActivity.equals(taskTop.task.realActivity)) {
//...这里的代码不执行
} else if ((launchFlags&Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) == 0) {
//...这里的代码不执行
} else if (!taskTop.task.rootWasReset) {
//...这里的代码不执行
}
// ==================== end
// 此时 addingToTask为true
if (!addingToTask && reuseTask == null) {
//...这里的代码不执行
}
}
}
}
//...
if (r.packageName != null) {
ActivityRecord top = topRunningNonDelayedActivityLocked(notTop);
if (top != null && r.resultTo == null) {
//此时task还没有B的ActivityRecord，故此不会进入下述分支
if (top.realActivity.equals(r.realActivity) && top.userId == r.userId) {
//...这里的代码不执行
}
}
} else {
//...这里的代码不执行
}
boolean newTask = false;
boolean keepCurTransition = false;
// 此时 r.resultTo == null addingToTask为true sourceRecord != null
if (r.resultTo == null && !addingToTask
&& (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
//...这里的代码不执行
} else if (sourceRecord != null) {
if (!addingToTask &&
(launchFlags&Intent.FLAG_ACTIVITY_CLEAR_TOP) != 0) {
//...这里的代码不执行
} else if (!addingToTask &&
(launchFlags&Intent.FLAG_ACTIVITY_REORDER_TO_FRONT) != 0) {
//...这里的代码不执行
}
//将B的ActivityRecord加入A的ActivityRecord所在的Task里
r.setTask(sourceRecord.task, sourceRecord.thumbHolder, false);
//...
} else {
//...这里的代码不执行
}
//...
startActivityLocked(r, newTask, doResume, keepCurTransition, options);
return ActivityManager.START_SUCCESS;
}
总结
从上面的分析可以看出来，Activity和Task的调度算法非常复杂，需结合实际场景才好分析，只有这样才知道是否需要新建Task,还是将新的ActivityRecord加入到已有的Task里，不过我们如果能理解启动模式的一些特点，对理解调度算法会有很大帮助。
大家可以结合下述场景分析调度算法:
1.从通知栏启动Activity:
假设应用有Activity A ，Activity A已启动，
此时发了一个通知，该通知用于启动Activity A，启动Activity A时不加任何特殊flag
点击通知，针对以下情况对任务调度情况进行分析:
Activity A的启动模式为standard
Activity A的启动模式为singleTop
Activity A的启动模式为singleTask
Activity A的启动模式为singleInstance
2.跨应用跳转Activity
假设应用app1有一个Activity A，另一个应用app2有一个Activity B
Activity A可跳转至Activity B
因为Activity A和Actiivty B在不同应用，所以Activity的taskffinity必然不同
现在Activity A已启动，跳转至Activity B，
针对以下4种情况分析跳转之后的Activity Task情况
Activity B的启动模式为standard
Activity B的启动模式为singleTop
Activity B的启动模式为singleTask
Activity B的启动模式为singleInstance
如果大家对上述场景分析有兴趣的话，可以在评论里一起探讨结果。
