一. 前言

        接上一篇文章 AMS组成 , 介绍了一下AMS的内部数据结构,  ProcessRecord容器,还有四大组件记录表 ,  本篇文章继续讲解一下与Activity管理相关的数据结构,  重点关注如下4个类文件:ActivityRecord   TaskRecord    ActivityStack  ActivityStackSupervisor

基本概念:

• ActivityRecord: 记录着Activity信息
• TaskRecord: 记录着task信息
• ActivityStack: 栈信息
• ActivityStackSupervisor : 栈管理者

二. ActivityRecord

        ActivityRecord，源码中的注释介绍：An entry in the history stack, representing an activity.翻译：历史栈中的一个条目，代表一个activity.

final class ActivityRecord extends ConfigurationContainer {
....final ActivityTaskManagerService mAtmService; // ownerfinal IApplicationToken.Stub appToken; // window manager tokenfinal ActivityInfo info; // all about me// TODO: This is duplicated state already contained in info.applicationInfo - removeApplicationInfo appInfo; // information about activity's app//ActivityRecord所在的TaskRecordTaskRecord task;        // the task this is in.//ActivityRecord的构造方法, 需要传递大量的信息ActivityRecord(ActivityTaskManagerService _service, WindowProcessController _caller,int _launchedFromPid, int _launchedFromUid, String _launchedFromPackage, Intent _intent,String _resolvedType, ActivityInfo aInfo, Configuration _configuration,ActivityRecord _resultTo, String _resultWho, int _reqCode, boolean _componentSpecified,boolean _rootVoiceInteraction, ActivityStackSupervisor supervisor,ActivityOptions options, ActivityRecord sourceRecord) {mAtmService = _service;mRootActivityContainer = _service.mRootActivityContainer;appToken = new Token(this, _intent);info = aInfo;launchedFromPid = _launchedFromPid;launchedFromUid = _launchedFromUid;launchedFromPackage = _launchedFromPackage;mUserId = UserHandle.getUserId(aInfo.applicationInfo.uid);intent = _intent;shortComponentName = _intent.getComponent().flattenToShortString();resolvedType = _resolvedType;componentSpecified = _componentSpecified;rootVoiceInteraction = _rootVoiceInteraction;mLastReportedConfiguration = new MergedConfiguration(_configuration);resultTo = _resultTo;resultWho = _resultWho;requestCode = _reqCode;//省略剩下的参数....
}

ActivityRecord中存在着大量的成员变量，包含了一个Activity的所有信息。
ActivityRecord中的成员变量task表示其所在的TaskRecord，由此可以看出：ActivityRecord与TaskRecord建立了联系.

列举出重要的成员变量

Activity类型

    / Activity type is currently not defined.  未定义类型*/public static final int ACTIVITY_TYPE_UNDEFINED = 0;/标准Activity类型 Standard activity type. Nothing special about the activity... */public static final int ACTIVITY_TYPE_STANDARD = 1;/ 桌面类型 Home/Launcher activity type. */public static final int ACTIVITY_TYPE_HOME = 2;/ 最近任务类型  Recents/Overview activity type. There is only one activity with this type in the system. */public static final int ACTIVITY_TYPE_RECENTS = 3;/ 辅助Activity类型Assistant activity type. */public static final int ACTIVITY_TYPE_ASSISTANT = 4;

Activity的状态ActivityState 

enum ActivityState {INITIALIZING,RESUMED,     //已恢复PAUSING,PAUSED,      //已暂停STOPPING, STOPPED,     //已停止FINISHING,DESTROYING,DESTROYED,   //已销毁RESTARTING_PROCESS}

时间相关的成员变量：

其中AR是指ActivityRecord, AS是指ActivityStack。

三. TaskRecord

         Task的信息记录在TaskRecord对象.

         TaskRecord，内部维护一个 ArrayList<ActivityRecord> 用来保存ActivityRecord。
frameworks/base/services/core/java/com/android/server/am/TaskRecord.java

 final int taskId;       // Unique identifier for this task. 任务ID/ List of all activities in the task arranged in history order *///使用一个ArrayList来保存所有的ActivityRecordfinal ArrayList<ActivityRecord> mActivities;//TaskRecord所在的ActivityStackprivate ActivityStack mStack; //构造方法
TaskRecord(ActivityTaskManagerService service, int _taskId, ActivityInfo info, Intent _intent,IVoiceInteractionSession _voiceSession, IVoiceInteractor _voiceInteractor) {mService = service;userId = UserHandle.getUserId(info.applicationInfo.uid);taskId = _taskId;lastActiveTime = SystemClock.elapsedRealtime();mAffiliatedTaskId = _taskId;voiceSession = _voiceSession;voiceInteractor = _voiceInteractor;isAvailable = true;mActivities = new ArrayList<>();mCallingUid = info.applicationInfo.uid;mCallingPackage = info.packageName;setIntent(_intent, info);setMinDimensions(info);touchActiveTime();mService.getTaskChangeNotificationController().notifyTaskCreated(_taskId, realActivity);}

列出重要的成员变量信息

四. ActivityStack

ActivityStack,内部维护了一个 ArrayList<TaskRecord> ，用来管理TaskRecord
 

class ActivityStack extends ConfigurationContainer {
...../* The back history of all previous (and possibly still* running) activities.  It contains #TaskRecord objects.*/// 使用一个ArrayList来保存TaskRecordprivate final ArrayList<TaskRecord> mTaskHistory = new ArrayList<>();//持有一个 ActivityStackSupervisor，所有的运行中的ActivityStacks都通过它来进行管protected final ActivityStackSupervisor mStackSupervisor;//构造方法TaskRecord createTaskRecord(int taskId, ActivityInfo info, Intent intent,IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,boolean toTop, ActivityRecord activity, ActivityRecord source,ActivityOptions options) {//创建一个taskfinal TaskRecord task = TaskRecord.create(mService, taskId, info, intent, voiceSession, voiceInteractor);// add the task to stack first, mTaskPositioner might need the stack association//将task添加到ActivityStack中去addTask(task, toTop, "createTaskRecord");final int displayId = mDisplayId != INVALID_DISPLAY ? mDisplayId : DEFAULT_DISPLAY;final boolean isLockscreenShown = mService.mStackSupervisor.getKeyguardController().isKeyguardOrAodShowing(displayId);if (!mStackSupervisor.getLaunchParamsController().layoutTask(task, info.windowLayout, activity, source, options)&& !matchParentBounds() && task.isResizeable() && !isLockscreenShown) {task.updateOverrideConfiguration(getRequestedOverrideBounds());}task.createTask(toTop, (info.flags & FLAG_SHOW_FOR_ALL_USERS) != 0);return task;}//添加Task到指定位置void addTask(final TaskRecord task, int position, boolean schedulePictureInPictureModeChange,String reason) {// TODO: Is this remove really needed? Need to look into the call path for the other addTask//若存在，先移除mTaskHistory.remove(task);if (isSingleTaskInstance() && !mTaskHistory.isEmpty()) {throw new IllegalStateException("Can only have one child on stack=" + this);}position = getAdjustedPositionForTask(task, position, null /* starting */);final boolean toTop = position >= mTaskHistory.size();final ActivityStack prevStack = preAddTask(task, reason, toTop);//添加task到mTaskHistorymTaskHistory.add(position, task);//为TaskRecord设置ActivityStacktask.setStack(this);updateTaskMovement(task, toTop);postAddTask(task, prevStack, schedulePictureInPictureModeChange);}
....
}

可以看到ActivityStack使用了一个ArrayList来保存TaskRecord。
另外，ActivityStack中还持有ActivityStackSupervisor对象，这个是用来管理ActivityStacks的。
ActivityStack是由ActivityStackSupervisor来创建的，实际ActivityStackSupervisor就是用来管理
ActivityStack的.

列出重要的成员变量信息

所有前台stack的mResumedActivity的state == RESUMED, 则表示allResumedActivitiesComplete, 此时mLastFocusedStack = mFocusedStack;

五. ActivityStackSupervisor

ActivityStackSupervisor，顾名思义，就是用来管理ActivityStack的
frameworks/base/services/core/java/com/android/server/wm/ActivityDisplay.java

class ActivityDisplay extends ConfigurationContainer<ActivityStack>implements WindowContainerListener {
....//管理的是Launcher相关的任务private ActivityStack mHomeStack = null; //管理的是Recent相关的任务栈private ActivityStack mRecentsStack = null;//画中画的任务栈private ActivityStack mPinnedStack = null;//分屏模式下的主屏幕栈private ActivityStack mSplitScreenPrimaryStack = null;
....
}

六. Activity栈关系

Activity栈结构体的组成关系:  点击查看大图

• 一般地，对于没有分屏功能以及虚拟屏的情况下，ActivityStackSupervisor与ActivityDisplay都是系统唯一；
• ActivityDisplay主要有Home Stack和App Stack这两个栈；
• 每个ActivityStack中可以有若干个TaskRecord对象；
• 每个TaskRecord包含如果个ActivityRecord对象；
• 每个ActivityRecord记录一个Activity信息。

(1)正向关系链表：

1. ActivityStackSupervisor.mActivityDisplays

2. -> ActivityDisplay.mStacks

3. -> ActivityStack.mTaskHistory

4. -> TaskRecord.mActivities

5. -> ActivityRecord

(2)反向关系链表：

1. ActivityRecord.task

2. -> TaskRecord.stack

3. -> ActivityStack.mStackSupervisor

4. -> ActivityStackSupervisor

注：ActivityStack.mDisplayId可找到所对应的ActivityDisplay；

七. 参考文章

 四大组件之ActivityRecord

AMS：ActivityRecord 理解