Android Activity.startActivity流程简介

1. 基本概念

1.1 Instrumentation是什么?

      顾名思义，仪器仪表，用于在应用程序中进行“测量”和“管理”工作。一个应用程序中只有一个Instrumentation实例对象，且每个Activity都有此对象的引用。Instrumentation将在任何应用程序运行前初始化，可以通过它监测系统与应用程序之间的所有交互，即类似于在系统与应用程序之间安装了个“窃听器”。

      当ActivityThread 创建(callActivityOnCreate)、暂停、恢复某个Activity时，通过调用此对象的方法来实现，如：

         1) 创建: callActivityOnCreate 

         2) 暂停: callActivityOnPause

         3) 恢复: callActivityOnResume

     Instrumentation和ActivityThread的关系，类似于老板与经理的关系，老板负责对外交流(如与Activity Manager Service<AMS>)，Instrumentation负责管理并完成老板交待的任务。

     它通过以下两个成员变量来对当前应用进程中的Activity进行管理：

    private List<ActivityWaiter> mWaitingActivities;
    private List<ActivityMonitor> mActivityMonitors;

    其功能函数下表所示：

功能	函数
增加删除Monitor	addMonitor(ActivityMonitor monitor) removeMonitor(ActivityMonitor monitor)
Application与Activity生命周期控制	newApplication(Class<?> clazz, Context context) newActivity(ClassLoader cl, String className,Intent intent) callActivityOnCreate(Activity activity, Bundle icicle) callActivityOnDestroy(Activity activity) callActivityOnStart(Activity activity) callActivityOnRestart(Activity activity) callActivityOnResume(Activity activity) callActivityOnStop(Activity activity) callActivityOnPause(Activity activity)
Instrumentation生命周期控制	onCreate(Bundle arguments) start() onStart() finish(int resultCode, Bundle results) onDestroy()
发送用户操控信息到当前窗口	sendCharacterSync(int keyCode) sendPointerSync(MotionEvent event) sendTrackballEventSync(MotionEvent event) sendTrackballEventSync(MotionEvent event)
同步操作	startActivitySync(Intent intent) //它调用Context.startActivity runOnMainSync(Runnable runner) waitForIdle()

2. Android应用程序启动过程(MainActivity)

     即MainActivity的启动过程，在此过程中，将创建一个新的进程来执行此MainActivity。

     Android应用程序从Launcher启动流程如下所示：

/*****************************************************************
 * Launcher通过Binder告诉ActivityManagerService，
 * 它将要启动一个新的Activity；
 ****************************************************************/
Launcher.startActivitySafely->  
Launcher.startActivity->  
 //要求在新的Task中启动此Activity  
 //intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)  
 Activity.startActivity->  
 Activity.startActivityForResult->  
 Instrumentation.execStartActivity->  
  // ActivityManagerNative.getDefault()返回AMS Proxy接口  
  ActivityManagerNative.getDefault().startActivity->  
  ActivityManagerProxy.startActivity->  
  
   ActivityManagerService.startActivity-> (AMS)  
   ActivityManagerService.startActivityAsUser->   
  
    ActivityStack.startActivityMayWait->  
    ActivityStack.resolveActivity(获取ActivityInfo)  
      //aInfo.name为main Activity,如：com.my.test.MainActivity  
      //aInfo.applicationInfo.packageName为包名，如com.my.test  
    ActivityStack.startActivityLocked->  
      //ProcessRecord callerApp; 调用者即Launcher信息  
      //ActivityRecord sourceRecord; Launcher Activity相关信息  
      //ActivityRecord r=new ActivityRecord(...)，将要创建的Activity相关信息    
    ActivityStack.startActivityUncheckedLocked->  
     //Activity启动方式：ActivityInfo.LAUNCH_MULTIPLE/LAUNCH_SINGLE_INSTANCE/  
     //             ActivityInfo.LAUNCH_SINGLE_TASK/LAUNCH_SINGLE_TOP)  
     // 创建一个新的task,即TaskRecord,并保存在ActivityRecord.task中  
     //r.setTask(new TaskRecord(mService.mCurTask, r.info, intent), null, true)  
     // 把新创建的Activity放在栈顶     
     ActivityStack.startActivityLocked->  
     ActivityStack.resumeTopActivityLocked->  
     ActivityStack.startPausingLocked (使Launcher进入Paused状态)->    

     /*****************************************************************
      * AMS通过Binder通知Launcher进入Paused状态
      ****************************************************************/
      ApplicationThreadProxy.schedulePauseActivity->   
      //private class ApplicationThread extends ApplicationThreadNative  
      ApplicationThread.schedulePauseActivity->  
  
       ActivityThread.queueOrSendMessage->  
   
       // 调用Activity.onUserLeaveHint  
       // 调用Activity.onPause  
       // 通知activity manager我进入了pause状态  
       ActivityThread.handlePauseActivity->  

       /*****************************************************************
        * Launcher通过Binder告诉AMS，它已经进入Paused状态
        ****************************************************************/
       ActivityManagerProxy.activityPaused->  
       ActivityManagerService.activityPaused->  
       ActivityStack.activityPaused->(把Activity状态修改为PAUSED)  
       ActivityStack.completePauseLocked->  
    
       // 参数为代表Launcher这个Activity的ActivityRecord  
       // 使用栈顶的Activity进入RESUME状态  
       ActivityStack.resumeTopActivityLokced->  
         //topRunningActivityLocked将刚创建的放于栈顶的activity取回来  
         // 即在ActivityStack.startActivityUncheckedLocked中创建的  

       /*****************************************************************
        * AMS创建一个新的进程，用来启动一个ActivityThread实例，
        * 即将要启动的Activity就是在这个ActivityThread实例中运行
        ****************************************************************/
       ActivityStack.startSpecificActivityLocked->  
  
        // 创建对应的ProcessRecord  
        ActivityManagerService.startProcessLocked->  
          
         // 启动一个新的进程  
         // 新的进程会导入android.app.ActivityThread类，并且执行它的main函数,  
         // 即实例化ActivityThread, 每个应用有且仅有一个ActivityThread实例  
         Process.start("android.app.ActivityThread",...)->  

         // 通过zygote机制创建一个新的进程  
         Process.startViaZygote->  
    
         // 这个函数在进程中创建一个ActivityThread实例，然后调用  
         // 它的attach函数，接着就进入消息循环  
         ActivityThread.main->  

         /*****************************************************************
          * ActivityThread通过Binder将一个ApplicationThread类的Binder对象
          * 传递给AMS，以便AMS通过此Binder对象来控制Activity整个生命周期
          ****************************************************************/
         ActivityThread.attach->  
         IActivityManager.attachApplication(mAppThread)->  
         ActivityManagerProxy.attachApplication->  
         ActivityManagerService.attachApplication->  
  
         // 把在ActivityManagerService.startProcessLocked中创建的ProcessRecord取出来  
         ActivityManagerService.attachApplicationLocked->  

         /*****************************************************************
          * AMS通过Binder通知ActivityThread一切准备OK,它可以真正启动新的Activity了
          ****************************************************************/            
         // 真正启动Activity  
         ActivityStack.realStartActivityLocked->  
         ApplicationThreadProxy.scheduleLaunchActivity->  
         ApplicationThread.scheduleLaunchActivity->  
         ActivityThread.handleLaunchActivity->  
           // 加载新的Activity类，并执行它的onCreate  
           ActivityThread.performLaunchActivity  
            /*1) Instrumentation.newActivity: 加载新类，即创建Activity对象； 
              2) ActivityClientRecord.packageInfo.makeApplication：创建Application对象； 
                 <LoadedApk.makeApplication> 
              3) Activity.attach(Context context, ActivityThread aThread, 
                    Instrumentation instr, IBinder token, int ident, 
                    Application application, Intent intent, ActivityInfo info, 
                    CharSequence title, Activity parent, String id, 
                    NonConfigurationInstances lastNonConfigurationInstances, 
                    Configuration config)：把Application attach到Activity, 即把Activtiy 
                                           相关信息设置到新创建的Activity中 
              4) Instrumentation.callActivityOnCreate：调用onCreate；*/  
    
           // 使用Activity进入RESUMED状态，并调用onResume  
           ActivityThread.handleResumeActivity  

3. ActivityManagerService

3.1 类中关键信息

public final class ActivityManagerService extends ActivityManagerNative
        implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
    ...
    // Maximum number of recent tasks that we can remember.
    static final int MAX_RECENT_TASKS = 20;

    public ActivityStack mMainStack; // 管理Activity堆栈

    // Whether we should show our dialogs (ANR, crash, etc) or just perform their
    // default actuion automatically.  Important for devices without direct input
    // devices.
    private boolean mShowDialogs = true;

    /**
     * Description of a request to start a new activity, which has been held
     * due to app switches being disabled.
     */
    static class PendingActivityLaunch {
        ActivityRecord r;
        ActivityRecord sourceRecord;
        int startFlags;
    }


    /**
     * Activity we have told the window manager to have key focus.
     */
    ActivityRecord mFocusedActivity = null;

    /**
     * List of intents that were used to start the most recent tasks.
     */
    final ArrayList<TaskRecord> mRecentTasks = new ArrayList<TaskRecord>();

    /**
     * Process management.
     */
    final ProcessList mProcessList = new ProcessList();

    /**
     * All of the applications we currently have running organized by name.
     * The keys are strings of the application package name (as
     * returned by the package manager), and the keys are ApplicationRecord
     * objects.
     */
    final ProcessMap<ProcessRecord> mProcessNames = new ProcessMap<ProcessRecord>();

    /**
     * The currently running isolated processes.
     */
    final SparseArray<ProcessRecord> mIsolatedProcesses = new SparseArray<ProcessRecord>();
    ...

    public static final Context main(int factoryTest) { //main入口函数
        AThread thr = new AThread();
        thr.start();

        synchronized (thr) {
            while (thr.mService == null) {
                try {
                    thr.wait();
                } catch (InterruptedException e) {
                }
            }
        }

        ActivityManagerService m = thr.mService;
        mSelf = m;
        ActivityThread at = ActivityThread.systemMain();
        mSystemThread = at;
        Context context = at.getSystemContext();
        context.setTheme(android.R.style.Theme_Holo);
        m.mContext = context;
        m.mFactoryTest = factoryTest;
        m.mMainStack = new ActivityStack(m, context, true); // 创建ActivityStack
        
        m.mBatteryStatsService.publish(context);
        m.mUsageStatsService.publish(context);
        
        synchronized (thr) {
            thr.mReady = true;
            thr.notifyAll();
        }

        m.startRunning(null, null, null, null);
        
        return context;
    }
}

3.2 家族图谱

4. ActivityStack-真正做事的家伙

    ActivityManagerService使用它来管理系统中所有的Activities的状态，Activities使用stack的方式进行管理。它是真正负责做事的家伙，很勤快的，但外界无人知道！

4.1 类中关键信息    

/**
 * State and management of a single stack of activities.
 */
final class ActivityStack {
    final ActivityManagerService mService;
    final boolean mMainStack;
    final Context mContext;

    enum ActivityState {
        INITIALIZING,
        RESUMED,
        PAUSING,
        PAUSED,
        STOPPING,
        STOPPED,
        FINISHING,
        DESTROYING,
        DESTROYED
    }

    /**
     * The back history of all previous (and possibly still
     * running) activities.  It contains HistoryRecord objects.
     */
    final ArrayList<ActivityRecord> mHistory = new ArrayList<ActivityRecord>();

    /**
     * Used for validating app tokens with window manager.
     */
    final ArrayList<IBinder> mValidateAppTokens = new ArrayList<IBinder>();

    /**
     * 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>();

    /**
     * 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 activities that are ready to be stopped, but waiting
     * for the next activity to settle down before doing so.  It contains
     * HistoryRecord objects.
     */
    final ArrayList<ActivityRecord> mStoppingActivities
            = new ArrayList<ActivityRecord>();

    /**
     * List of activities that are in the process of going to sleep.
     */
    final ArrayList<ActivityRecord> mGoingToSleepActivities
            = 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;

    /**
     * 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;

    /**
     * Set to indicate whether to issue an onUserLeaving callback when a
     * newly launched activity is being brought in front of us.
     */
    boolean mUserLeaving = false;

    ActivityStack(ActivityManagerService service, Context context, boolean mainStack) {
        mService = service;
        mContext = context;
        mMainStack = mainStack;
        ...
    }
    ...
}

4.2 家族图谱

5. ProcessRecord

      记录了一个进程的相关信息。

5.1 类中关键信息

/**
 * Full information about a particular process that
 * is currently running.
 */
class ProcessRecord {
    final ApplicationInfo info; // all about the first app in the process
    final boolean isolated;     // true if this is a special isolated process
    final int uid;              // uid of process; may be different from 'info' if isolated
    final int userId;           // user of process.
    final String processName;   // name of the process

    IApplicationThread thread;  // the actual proc...  may be null only if
                                // 'persistent' is true (in which case we
                                // are in the process of launching the app)
                                // 是ApplicationThread对象的远程接口,
                                // 通过此接口通知Activity进入对应的状态
                                
    int pid;                    // The process of this application; 0 if none
    

    ApplicationInfo instrumentationInfo; // the application being instrumented

    BroadcastRecord curReceiver;// receiver currently running in the app

    // contains HistoryRecord objects
    final ArrayList<ActivityRecord> activities = new ArrayList<ActivityRecord>();

    // all ServiceRecord running in this process
    final HashSet<ServiceRecord> services = new HashSet<ServiceRecord>();

    // services that are currently executing code (need to remain foreground).
    final HashSet<ServiceRecord> executingServices
             = new HashSet<ServiceRecord>();

    // All ConnectionRecord this process holds
    final HashSet<ConnectionRecord> connections
            = new HashSet<ConnectionRecord>();  

    // all IIntentReceivers that are registered from this process.
    final HashSet<ReceiverList> receivers = new HashSet<ReceiverList>();

    // class (String) -> ContentProviderRecord
    final HashMap<String, ContentProviderRecord> pubProviders
            = new HashMap<String, ContentProviderRecord>(); 

    // All ContentProviderRecord process is using
    final ArrayList<ContentProviderConnection> conProviders
            = new ArrayList<ContentProviderConnection>();
    
    boolean persistent;         // always keep this application running?
    boolean crashing;           // are we in the process of crashing?
    Dialog crashDialog;         // dialog being displayed due to crash.
    boolean notResponding;      // does the app have a not responding dialog?
    Dialog anrDialog;           // dialog being displayed due to app not resp.
    boolean removed;            // has app package been removed from device?
    boolean debugging;          // was app launched for debugging?
    boolean waitedForDebugger;  // has process show wait for debugger dialog?
    Dialog waitDialog;          // current wait for debugger dialog

    ProcessRecord(BatteryStatsImpl.Uid.Proc _batteryStats, IApplicationThread _thread,
            ApplicationInfo _info, String _processName, int _uid) {
        batteryStats = _batteryStats;
        info = _info;
        isolated = _info.uid != _uid;
        uid = _uid;
        userId = UserHandle.getUserId(_uid);
        processName = _processName;
        pkgList.add(_info.packageName);
        thread = _thread;
        maxAdj = ProcessList.HIDDEN_APP_MAX_ADJ;
        hiddenAdj = clientHiddenAdj = emptyAdj = ProcessList.HIDDEN_APP_MIN_ADJ;
        curRawAdj = setRawAdj = -100;
        curAdj = setAdj = -100;
        persistent = false;
        removed = false;
    }
    ...
}

5. 2 家族图谱

6. IApplicationThread接口AMS->Application

    IApplicationThread为AMS作为客户端访问Application服务器端的Binder接口。当创建Application时，将把此Binder对象传递给AMS，然后AMS把它保存在mProcessNames.ProcessRecord.thread中。当需要通知Application工作时，则调用IApplicationThread中对应的接口函数。

   其相互关系如下图所示：