本文主要介紹android4.4中ActivityManagerService的啟動(dòng)和ActivityManagerService對(duì)Activity堆棧的管理。

一、ActivityManagerService的啟動(dòng)

ActivityManagerService也是在SystemServer啟動(dòng)的時(shí)候創(chuàng)建的，

<span style="font-size:18px;">class ServerThread {.......public void initAndLoop() {......context = ActivityManagerService.main(factoryTest); //啟動(dòng)AMS.......ActivityManagerService.setSystemProcess(); //向Service Manager注冊(cè).......}}</span>

需要在一個(gè)新線程中初始化ActivityManagerService，ActivityManagerService用了單例模式。

<span style="font-size:18px;"> public static final Context main(int factoryTest) { AThread thr = new AThread(); thr.start(); //啟動(dòng)一個(gè)線程來(lái)啟動(dòng) synchronized (thr) { while (thr.mService == null) { try { thr.wait();//線程等待activitymanagerservice初始化完成 } catch (InterruptedException e) { } } } ActivityManagerService m = thr.mService; mSelf = m; ActivityThread at = ActivityThread.systemMain(); //啟動(dòng)一個(gè)主線程 mSystemThread = at; Context context = at.getSystemContext(); context.setTheme(android.R.style.Theme_Holo); ...... m.mStackSupervisor = new ActivityStackSupervisor(m, context, thr.mLooper); //新建一個(gè)activity堆棧管理輔助類實(shí)例 ....... synchronized (thr) { thr.mReady = true; thr.notifyAll(); //activitymanagerservice啟動(dòng)完成 } m.startRunning(null, null, null, null); return context;}</span>

二、ActivityStackSupervisor和 ActivityStack 管理Activity的狀態(tài)

1.ActivityState

描述一個(gè)Activity可能經(jīng)歷的所有狀態(tài)，定義在ActivityStack.java文件中：

enum ActivityState { INITIALIZING, //正在初始化 RESUMED, //已經(jīng)恢復(fù) PAUSING, //正在暫停 PAUSED, //已經(jīng)暫停 STOPPING, //正在停止 STOPPED, //已經(jīng)停止 FINISHING, //正在完成 DESTROYING, //正在銷毀 DESTROYED //已經(jīng)銷毀}

狀態(tài)變換圖:

/*** The back history of all previous (and possibly still* running) activities. It contains #TaskRecord objects.*/private ArrayList<TaskRecord> mTaskHistory = new ArrayList<TaskRecord>();/*** Used for validating app tokens with window manager.*/final ArrayList<TaskGroup> mValidateAppTokens = new ArrayList<TaskGroup>();/*** List of running activities, sorted by recent usage.* The first entry in the list is the least recently used.* It contains HistoryRecord objects.*/final ArrayList<ActivityRecord> mLRUActivities = new ArrayList<ActivityRecord>();/*** Animations that for the current transition have requested not to* be considered for the transition animation.*/final ArrayList<ActivityRecord> mNoAnimActivities = new ArrayList<ActivityRecord>();/*** When we are in the process of pausing an activity, before starting the* next one, this variable holds the activity that is currently being paused.*/ActivityRecord mPausingActivity = null;/*** This is the last activity that we put into the paused state. This is* used to determine if we need to do an activity transition while sleeping,* when we normally hold the top activity paused.*/ActivityRecord mLastPausedActivity = null;/*** Activities that specify No History must be removed once the user navigates away from them.* If the device goes to sleep with such an activity in the paused state then we save it here* and finish it later if another activity replaces it on wakeup.*/ActivityRecord mLastNoHistoryActivity = null;/*** Current activity that is resumed, or null if there is none.*/ActivityRecord mResumedActivity = null;/*** This is the last activity that has been started. It is only used to* identify when multiple activities are started at once so that the user* can be warned they may not be in the activity they think they are.*/ActivityRecord mLastStartedActivity = null;

ActivityRecord變量的具體含義，可查看注釋。

2.記錄Activity的ArrayList和ActivityStack

/** The stack containing the launcher app */ private ActivityStack mHomeStack; /** The non-home stack currently receiving input or launching the next activity. If home is * in front then mHomeStack overrides mFocusedStack. * DO NOT ACCESS DIRECTLY - It may be null, use getFocusedStack() */ private ActivityStack mFocusedStack; /** All the non-launcher stacks */ private ArrayList<ActivityStack> mStacks = new ArrayList<ActivityStack>();

mHomeStack : 只記錄存放Launcher和SystemUI(最近應(yīng)用)的Task

mFocusedStack ： 記錄所有非Launcher App的Task

mStacks : 這個(gè)ArrayList只存放 mHomeStack和 mFocusedStack， mHomeStack 放在第0個(gè)位置

這個(gè)結(jié)果我是在用adb shell dumpsys activity命令查看而得知：

ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities)Stack #0:Task id #1TaskRecord{b22161f0 #1 A=com.android.launcher U=0 sz=1}Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10200000 cmp=com.android.launcher/com.android.launcher2.Launcher }Hist #0: ActivityRecord{b2214570 u0 com.android.launcher/com.android.launcher2.Launcher t1}Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10000000 cmp=com.android.launcher/com.android.launcher2.Launcher }ProcessRecord{b21df5c8 1402:com.android.launcher/u0a8}Task id #3TaskRecord{b2288fd0 #3 A=com.android.systemui U=0 sz=1}Intent { act=com.android.systemui.recent.action.TOGGLE_RECENTS flg=0x10800000 cmp=com.android.systemui/.recent.RecentsActivity bnds=[132,331][296,476] (has extras) }Hist #0: ActivityRecord{b22d5aa0 u0 com.android.systemui/.recent.RecentsActivity t3}Intent { act=com.android.systemui.recent.action.TOGGLE_RECENTS flg=0x10800000 cmp=com.android.systemui/.recent.RecentsActivity bnds=[132,331][296,476] (has extras) }ProcessRecord{b2169ac8 1313:com.android.systemui/u0a7}Running activities (most recent first):TaskRecord{b22161f0 #1 A=com.android.launcher U=0 sz=1}Run #1: ActivityRecord{b2214570 u0 com.android.launcher/com.android.launcher2.Launcher t1}TaskRecord{b2288fd0 #3 A=com.android.systemui U=0 sz=1}Run #0: ActivityRecord{b22d5aa0 u0 com.android.systemui/.recent.RecentsActivity t3}Stack #1:Task id #4TaskRecord{b21e57d0 #4 A=android.task.contacts U=0 sz=1}Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.android.contacts/.activities.PeopleActivity }Hist #0: ActivityRecord{b2281e68 u0 com.android.contacts/.activities.PeopleActivity t4}Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.android.contacts/.activities.PeopleActivity bnds=[64,417][128,481] }ProcessRecord{b22f66c0 1820:com.android.contacts/u0a2}Task id #2TaskRecord{b2229370 #2 A=com.android.dialer U=0 sz=1}Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.android.dialer/.DialtactsActivity }Hist #0: ActivityRecord{b223d3c8 u0 com.android.dialer/.DialtactsActivity t2}Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.android.dialer/.DialtactsActivity bnds=[0,417][64,481] }ProcessRecord{b2215d48 1569:com.android.dialer/u0a4}Running activities (most recent first):TaskRecord{b21e57d0 #4 A=android.task.contacts U=0 sz=1}Run #1: ActivityRecord{b2281e68 u0 com.android.contacts/.activities.PeopleActivity t4}TaskRecord{b2229370 #2 A=com.android.dialer U=0 sz=1}Run #0: ActivityRecord{b223d3c8 u0 com.android.dialer/.DialtactsActivity t2}mResumedActivity: ActivityRecord{b2281e68 u0 com.android.contacts/.activities.PeopleActivity t4}mFocusedActivity: ActivityRecord{b2281e68 u0 com.android.contacts/.activities.PeopleActivity t4}mDismissKeyguardOnNextActivity:falsemStackState=STACK_STATE_HOME_IN_BACKmSleepTimeout: falsemCurTaskId: 4mUserStackInFront: {}Recent tasks:* Recent #0: TaskRecord{b21e57d0 #4 A=android.task.contacts U=0 sz=1}* Recent #1: TaskRecord{b22161f0 #1 A=com.android.launcher U=0 sz=1}* Recent #2: TaskRecord{b2229370 #2 A=com.android.dialer U=0 sz=1}* Recent #3: TaskRecord{b2288fd0 #3 A=com.android.systemui U=0 sz=1}

Stack #0 就是

mHomeStack，里面放了Launcher和SystemUI的task。

Stack #1 就是 mFocusedStack，放了所有已經(jīng)啟動(dòng)的app的task。

這兩個(gè)就是mStacks里面存放的。

3.現(xiàn)在看看 mHomeStack和 mFocusedStack是什么時(shí)候被放入mStacks里的？ mHomeStack和 mFocusedStack 里面的元素是在哪里加入的？

mHomeStack的初始化是在開機(jī)時(shí)，WindowManagerService創(chuàng)建完成后，ActivityManagerService設(shè)置 WindowManagerService時(shí)，

ActivityManagerService.self().setWindowManager(wm); //SystemServer.java中 public void setWindowManager(WindowManagerService wm) { //<font size="4"><font size="4"><font size="4"><span style="font-size:18px;"><span style="font-size:18px;"><span style="font-size:18px;">ActivityManagerService</span></span></span></font></font>.java</font>中mWindowManager = wm;mStackSupervisor.setWindowManager(wm);wm.createStack(HOME_STACK_ID, -1, StackBox.TASK_STACK_GOES_OVER, 1.0f);} void setWindowManager(WindowManagerService wm) { //ActivityStackSupervisor.java中mWindowManager = wm;mHomeStack = new ActivityStack(mService, mContext, mLooper, HOME_STACK_ID);mStacks.add(mHomeStack); //放在了第0個(gè)位置} Android4.4 framework分析——Launcher中啟動(dòng)應(yīng)用程序(startActivity)的過程

mFocusedStack存放的是應(yīng)用程序的task，所以它的創(chuàng)建是在Activity啟動(dòng)的時(shí)候，Activity的啟動(dòng)過程可以參考step16，startActivityUncheckedLocked()中，

if (r.resultTo == null && !addingToTask&& (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {targetStack = adjustStackFocus(r); //targetStack即目標(biāo)Stack，r要加入的stack ActivityStack adjustStackFocus(ActivityRecord r) { final TaskRecord task = r.task; //r是否是應(yīng)用程序的activity類型，或者r所屬task是應(yīng)用程序task //android定義區(qū)分了三種不同的activity類型 //static final int APPLICATION_ACTIVITY_TYPE = 0; //應(yīng)用程序類型 //static final int HOME_ACTIVITY_TYPE = 1; //Launcher類型 //static final int RECENTS_ACTIVITY_TYPE = 2; //SystemUI的最近應(yīng)用 if (r.isApplicationActivity() || (task != null && task.isApplicationTask())) { if (task != null) { if (mFocusedStack != task.stack) { if (DEBUG_FOCUS || DEBUG_STACK) Slog.d(TAG, "adjustStackFocus: Setting focused stack to r=" + r + " task=" + task); mFocusedStack = task.stack; } else { if (DEBUG_FOCUS || DEBUG_STACK) Slog.d(TAG, "adjustStackFocus: Focused stack already=" + mFocusedStack); } return mFocusedStack;//app類型的activity每次都加入mFocusedStack } if (mFocusedStack != null) { if (DEBUG_FOCUS || DEBUG_STACK) Slog.d(TAG, "adjustStackFocus: Have a focused stack=" + mFocusedStack); return mFocusedStack;//app類型的activity每次都加入mFocusedStack } for (int stackNdx = mStacks.size() - 1; stackNdx > 0; --stackNdx) { ActivityStack stack = mStacks.get(stackNdx); if (!stack.isHomeStack()) { if (DEBUG_FOCUS || DEBUG_STACK) Slog.d(TAG, "adjustStackFocus: Setting focused stack=" + stack); mFocusedStack = stack; return mFocusedStack;//app類型的activity每次都加入mFocusedStack } } // Time to create the first app stack for this user. int stackId = mService.createStack(-1, HOME_STACK_ID, //啟動(dòng)第一個(gè)app，需要?jiǎng)?chuàng)建一個(gè)stack，其他app創(chuàng)建時(shí)，前面條件判斷將攔截住 StackBox.TASK_STACK_GOES_OVER, 1.0f); if (DEBUG_FOCUS || DEBUG_STACK) Slog.d(TAG, "adjustStackFocus: New stack r=" + r + " stackId=" + stackId); mFocusedStack = getStack(stackId); return mFocusedStack; //app類型的activity每次都加入mFocusedStack } return mHomeStack;}

從上面這個(gè)方法看出，Launcher類型和最近應(yīng)用類型的task將加入mHomeStack中，而其他應(yīng)用類型的task加入mFocusedStack，

public int createStack(int taskId, int relativeStackBoxId, int position, float weight) { enforceCallingPermission(android.Manifest.permission.MANAGE_ACTIVITY_STACKS, "createStack()"); synchronized (this) { long ident = Binder.clearCallingIdentity(); try { int stackId = mStackSupervisor.createStack(); //看這里 mWindowManager.createStack(stackId, relativeStackBoxId, position, weight); if (taskId > 0) { moveTaskToStack(taskId, stackId, true); } return stackId; } finally { Binder.restoreCallingIdentity(ident); } } } int createStack() { while (true) { if (++mLastStackId <= HOME_STACK_ID) { mLastStackId = HOME_STACK_ID + 1; } if (getStack(mLastStackId) == null) { break; } } mStacks.add(new ActivityStack(mService, mContext, mLooper, mLastStackId)); //新建了一個(gè)Stack加入mStacks return mLastStackId; }

createStack()方法只有一次機(jī)會(huì)執(zhí)行，即第一次運(yùn)行app。

mStacks里什么情況下會(huì)出現(xiàn)第三或第四個(gè)元素，這個(gè)不知道，目前沒有發(fā)現(xiàn)這種情況。。。

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