ActivityManagerService要管理四大组件，那四大组件就必须在AMS中有存在的形式，这里先从AMS 如何管理Activity 谈起；
Activity在AMS 中存在的形式为ActivityRecord；
AMS以Task的方式管理Activity，Task在AMS存在的形式为TaskRecord；TaskRecord中的mActivities用栈的方式管理ActivityRecord；
TaskRecord在AMS中依靠ActivityStack去管理，从命名来看，ActivityStack更像Activity栈，但是ActivityStack并不是Activity 栈，而是负责管理TaskRecord的类，android系统中有三种ActivityStack（mHomeStack，mFocusedStack，mLastFocusedStack）；
ActivityStack同样有管理者，ActivityStackSupervisor负责管理ActivityStack；
每一个Activity和TaskRecord 都是属于某个进程，所以进程还需要在AMS有存在形式，
进程在AMS中存在的形式就是ProcessRecord；
一、主要涉及4个类
1) ActivityRecord
源码注释：An entry in the history stack, representing an activity.
翻译一下：存在历史栈的一个实例，代表一个Activity。
2) TaskRecord
Activity栈，内部维护一个ArrayList<ActivityRecord>
3) ActivityStack
并不是一个Activity栈，真正意义上的Activity栈是TaskRecord，这个类是负责管理各个Activity栈，内部维护一个ArrayList<TaskRecord>
4) ActivityStackSupervisor
内部持有一个ActivityStack，而ActivityStack内部也持有ActivityStackSupervisor，相当于ActivityStack的辅助管理类
ActivityRecord
ActivityRecord是Activity在AMS中的存在形式，ActivityRecord保存了Activity的信息。
final class ActivityRecord { TaskRecord task; // the task this is in. final IApplicationToken.Stub appToken; final int userId; int theme; int launchMode; ... }
成员变量task表示自己所在的TaskRecord，这样要找到自己所在的TaskRecord就不必遍历查找了。
TaskRecord
我们都知道AMS以Task的方式在管理Activity，TaskRecord中的mActivities是一个栈，它的作用是以栈的方式组织管理Activity。Android把用户一次操作相关的Activity按照先后顺序保存在一个Task中，这个Task在AMS中的存在形式就是TaskRecord；
final class TaskRecord { ........... final int taskId; // Unique identifier for this task. int mAffiliatedTaskId; // taskId of parent affiliation or self if no parent. // 是指root activity的affinity，即该Task中第一个Activity; 可以理解为当前task的name； String affinity; // The affinity name for this task, or null; may change identity. // 启动这个task的intent Intent intent; // The original intent that started the task. long firstActiveTime; // First time this task was active. long lastActiveTime; // Last time this task was active, including sleep. boolean inRecents; // Actually in the recents list? boolean isAvailable; // Is the activity available to be launched? // task模式 int mLockTaskMode; // Which tasklock mode to launch this task in. One of // ActivityManager.LOCK_TASK_LAUNCH_MODE_* /** List of all activities in the task arranged in history order */ // 该Task中所有的Activity final ArrayList<ActivityRecord> mActivities; /** Current stack */ // 管理该Task的ActivityStack ActivityStack stack; // 最近列表中,可以看到当前Task的缩略图 private Bitmap mLastThumbnail; // Last thumbnail captured for this item. private final File mLastThumbnailFile; // File containing last thumbnail. final ActivityManagerService mService; .......... }
TaskRecord 的affinity只有在其被创建的时候才有用，以后加入这个Task的Activity，即使他们通过taskAffinity指定了一个不同的字符串，也不会更改Task的名称；Activity所在的Task通过AndroidManifest.xml中<Activity>标签中的android:taskAffinity=”xxx”来指定，通常不去主动设置一个Activity的taskAffinity属性，那么taskAffinity的值缺省使用包名。正因为如此，应用中所有的Activity的taskAffinity属性值默认都是相同的，都是包名，所以在应用中使用FLAG_ACTIVITY_NEW_TASK标志去启动一个本应用中的一个Activity，也不会创建一个新的task，除非这个Activity 额外指定了不同的taskAffinity属性值；
ActivityStack
ActivityStack充当TaskRecord的Manager角色；
final class ActivityStack { private final ArrayList<TaskRecord> mTaskHistory = new ArrayList<>(); //ActivityStack中所有的TaskRecord private final ArrayList<ActivityRecord> mLRUActivities = new ArrayList<>();//最近活动过的ActivityRecord ...... final int mStackId; //ActivityStack的唯一标识 final ActivityContainer mActivityContainer; /** The other stacks, in order, on the attached display. Updated at attach/detach time. */ ArrayList<ActivityStack> mStacks; //绑定的ActivityDisplay中的所有ActivityStack /** The attached Display's unique identifier, or -1 if detached */ int mDisplayId;//绑定的ActivityDisplay的id，默认为Display.DEFAULT_DISPLAY = 0； ...... /** Run all ActivityStacks through this */ final ActivityStackSupervisor mStackSupervisor; //ActivityStack的管理者ActivityStackSupervisor ActivityStack(ActivityStackSupervisor.ActivityContainer activityContainer, RecentTasks recentTasks) { mStackSupervisor = activityContainer.getOuter(); ... } }
mTaskHistory：是一个列表，存储的是ActivityStack中的所有TaskRecord对象，TaskRecord 通过mActivities变量存储Task中所有的Activity，所以mTaskHistory间接管理了ActivityStack中的所有activity；
mLRUActivities：一个列表，存储的是ActivityStack中按照最近活动情况运行的所有Activity；
ActivityStackSupervisor
ActivityStackSupervisor 用于管理ActivityStack；ActivityStackSupervisor为AMS提供管理方法；管理着系统中的三个ActivityStack；
public final class ActivityStackSupervisor {/** The stack containing the launcher app. Assumed to always be attached to * Display.DEFAULT_DISPLAY. */ private ActivityStack mHomeStack; /** The stack currently receiving input or launching the next activity. */ private ActivityStack mFocusedStack; /** If this is the same as mFocusedStack then the activity on the top of the focused stack has * been resumed. If stacks are changing position this will hold the old stack until the new * stack becomes resumed after which it will be set to mFocusedStack. */ private ActivityStack mLastFocusedStack; /** List of activities that are waiting for a new activity to become visible before completing * whatever operation they are supposed to do. */ final ArrayList<ActivityRecord> mWaitingVisibleActivities = new ArrayList<ActivityRecord>(); /** List of processes waiting to find out about the next visible activity. */ final ArrayList<IActivityManager.WaitResult> mWaitingActivityVisible = new ArrayList<IActivityManager.WaitResult>(); /** List of processes waiting to find out about the next launched activity. */ final ArrayList<IActivityManager.WaitResult> mWaitingActivityLaunched = new ArrayList<IActivityManager.WaitResult>(); /** List of activities that are ready to be stopped, but waiting for the next activity to * settle down before doing so. */ final ArrayList<ActivityRecord> mStoppingActivities = new ArrayList<ActivityRecord>(); /** List of activities that are ready to be finished, but waiting for the previous activity to * settle down before doing so. It contains ActivityRecord objects. */ final ArrayList<ActivityRecord> mFinishingActivities = new ArrayList<ActivityRecord>(); /** List of activities that are in the process of going to sleep. */ final ArrayList<ActivityRecord> mGoingToSleepActivities = new ArrayList<ActivityRecord>(); ...... /** Mapping from (ActivityStack/TaskStack).mStackId to their current state */ private SparseArray<ActivityContainer> mActivityContainers = new SparseArray<ActivityContainer>();//以mStackId为key /** Mapping from displayId to display current state */ private final SparseArray<ActivityDisplay> mActivityDisplays = new SparseArray<ActivityDisplay>();//以displayId为key }
AMS使用mHomeStack，mFocusedStack来完成系统全部的Activity的管理和调度。其中mHomeStack管理的是Launcher相关的任务，包括Launcher、RecentTask，Keyguad,除了上述以外的任务都归mFocusedStack管理。
AMS 通过操作ActivityStackSupervisor来管理Activity；具体是如何操作的呢？ActivityStackSupervisor通过ActivityContainer来管理ActivityStack(ActivityStack的构造方法只有在ActivityContainer的构造方法中被调用)，ActivityContainer关联ActivityDisplay，ActivityDisplay将自己的mStacks赋值给ActivityContainer的mStack；mStack.mStacks = activityDisplay.mStacks； ActivityContainer
class ActivityContainer extends android.app.IActivityContainer.Stub { final static int FORCE_NEW_TASK_FLAGS = Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_MULTIPLE_TASK | Intent.FLAG_ACTIVITY_NO_ANIMATION; final int mStackId; IActivityContainerCallback mCallback = null; final ActivityStack mStack; //ActivityContainer用于维护ActivityStack的 ActivityRecord mParentActivity = null; String mIdString; boolean mVisible = true; /** Display this ActivityStack is currently on. Null if not attached to a Display. */ ActivityDisplay mActivityDisplay; final static int CONTAINER_STATE_HAS_SURFACE = 0; final static int CONTAINER_STATE_NO_SURFACE = 1; final static int CONTAINER_STATE_FINISHING = 2; int mContainerState = CONTAINER_STATE_HAS_SURFACE; ActivityContainer(int stackId) { synchronized (mService) { mStackId = stackId; mStack = new ActivityStack(this); mIdString = "ActivtyContainer{" + mStackId + "}"; if (DEBUG_STACK) Slog.d(TAG, "Creating " + this); } } void attachToDisplayLocked(ActivityDisplay activityDisplay) { //ActivityContainer关联ActivityDisplay，用 if (DEBUG_STACK) Slog.d(TAG, "attachToDisplayLocked: " + this + " to display=" + activityDisplay); mActivityDisplay = activityDisplay; mStack.mDisplayId = activityDisplay.mDisplayId; mStack.mStacks = activityDisplay.mStacks; activityDisplay.attachActivities(mStack); mWindowManager.attachStack(mStackId, activityDisplay.mDisplayId); } ...... ------>/frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java /** Exactly one of these classes per Display in the system. Capable of holding zero or more * attached {@link ActivityStack}s */ class ActivityDisplay { /** Actual Display this object tracks. */ int mDisplayId; Display mDisplay; DisplayInfo mDisplayInfo = new DisplayInfo(); /** All of the stacks on this display. Order matters, topmost stack is in front of all other * stacks, bottommost behind. Accessed directly by ActivityManager package classes */ final ArrayList<ActivityStack> mStacks = new ArrayList<ActivityStack>(); ActivityRecord mVisibleBehindActivity; ActivityDisplay() { } // After instantiation, check that mDisplay is not null before using this. The alternative // is for this to throw an exception if mDisplayManager.getDisplay() returns null. ActivityDisplay(int displayId) { final Display display = mDisplayManager.getDisplay(displayId); if (display == null) { return; } init(display); } ....... void attachActivities(ActivityStack stack) { if (DEBUG_STACK) Slog.v(TAG, "attachActivities: attaching " + stack + " to displayId=" + mDisplayId); mStacks.add(stack); } ......
追踪代码，发现ActivityContainer在ActivitySupervisor的createStackOnDisplay中被初始化，createStackOnDisplay在setWindowManager或adjustStackFocus或restoreRecentTaskLocked中被调用；这里说说从setWindowManager开始的调用流程，setWindowManager在SystemServer启动AMS时调用，然后调用ActivityContainer.attachToDisplayLocked方法；流程的大概就是根据mDisplayId获取ActivityDisplay，将ActivityDisplay的mStacks(代表该Display上的所有activitystack) 赋值给ActivityContainer的mStack的mStacks；同时将调用activityDisplay.attachActivities(mStack)将ActivityContainer的mStack(ActivityContainer维护的ActivityStack)添加到ActivityDisplay的mStacks 中； ActivityStackSupervisor对ActivityRecord的管理过程如下：
ActivityStackSupervisor.mActivityDisplays -> ActivityDisplay.mStacks -> ActivityStack.mTaskHistory -> TaskRecord.mActivities -> ActivityRecord
二、场景解析
1、从桌面第一次启动App
startActivityLocked里构造一个ActivityRecord
新建一个TaskRecord，并存入mTaskHistory
ActivityRecord存入mActivities
final int startActivityUncheckedLocked(...) { final int startActivityUncheckedLocked(...) { if (reuseTask == null) { r.setTask(targetStack.createTaskRecord(...); ... targetStack.startActivityLocked(r, newTask, doResume, keepCurTransition, options); ... } }
1.TaskRecord存入mTaskHistory
TaskRecord createTaskRecord(int taskId, ActivityInfo info, Intent intent, IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, boolean toTop) { TaskRecord task = new TaskRecord(mService, taskId, info, intent, voiceSession, voiceInteractor); addTask(task, toTop, false); return task; } void addTask(final TaskRecord task, final boolean toTop, boolean moving) { task.stack = this; if (toTop) { insertTaskAtTop(task, null); } else { mTaskHistory.add(0, task); updateTaskMovement(task, false); } ... } private void insertTaskAtTop(TaskRecord task, ActivityRecord newActivity) { ... mTaskHistory.add(taskNdx, task); updateTaskMovement(task, true); }
2.ActivityRecord存入mActivities
final void startActivityLocked(ActivityRecord r, boolean newTask, ...) { ... task = mTaskHistory.get(taskNdx); ... task.addActivityToTop(r); } void addActivityToTop(ActivityRecord r) { addActivityAtIndex(mActivities.size(), r); } void addActivityAtIndex(int index, ActivityRecord r) { ... mActivities.add(index, r); ... }
