Activityの起動手順をソースコードの観点から説明する


Activityの起動手順をソースコードの観点から説明する
ActivityはAndroidの4つのコンポーネントの1つとして、私たちが普段開発している最も多くのコンポーネントでもあります.4つのコンポーネントの中で最も重要なボスとして、Activityはどのように起動したのでしょうか.この文章はソースコードの角度から簡単にみんなのために解析します.(PS:本明細書のソースコードは7.0システムに基づいている)
一般にActivityを起動するには2つの方法がありますが、ここではこの2つの方法を詳しく説明しませんが、同じ論理startActivity()メソッドを呼び出しています.そこでActivityの起動プロセスを分析するのはこの方法から始めます.下のstartActivity()のソースコードを見てください.
  @Override
    public void startActivity(Intent intent) {
        this.startActivity(intent, null);
    }

    @Override
    public void startActivity(Intent intent, @Nullable Bundle options) {
        if (options != null) {
            startActivityForResult(intent, -1, options);
        } else {
            // Note we want to go through this call for compatibility with
            // applications that may have overridden the method.
            startActivityForResult(intent, -1);
        }
    }
startActivity()には複数のリロードメソッドが表示されますが、最終的に呼び出されるのはstartActivity ForResult()メソッドです.次に、ソースコードのstartActivity ForResult()の実装を見てみましょう.
 public void startActivityForResult(@RequiresPermission Intent intent, int requestCode) {
        startActivityForResult(intent, requestCode, null);
    }

    public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
            @Nullable Bundle options) {
        //mParent   Activity  ,   Activity    Activity  
        if (mParent == null) {
            //       Activity,      mMainThread.getApplicationThread()     
            Instrumentation.ActivityResult ar =
                mInstrumentation.execStartActivity(
                    this, mMainThread.getApplicationThread(), mToken, this,
                    intent, requestCode, options);
            if (ar != null) {
                //    , onActivityResult      
                mMainThread.sendActivityResult(
                    mToken, mEmbeddedID, requestCode, ar.getResultCode(),
                    ar.getResultData());
            }
            //      requestCode   
            if (requestCode >= 0) {
                // If this start is requesting a result, we can avoid making
                // the activity visible until the result is received.  Setting
                // this code during onCreate(Bundle savedInstanceState) or onResume() will keep the
                // activity hidden during this time, to avoid flickering.
                // This can only be done when a result is requested because
                // that guarantees we will get information back when the
                // activity is finished, no matter what happens to it.
                mStartedActivity = true;
            }

            cancelInputsAndStartExitTransition(options);
            // TODO Consider clearing/flushing other event sources and events for child windows.
        } else {
            if (options != null) {
                mParent.startActivityFromChild(this, intent, requestCode, options);
            } else {
                // Note we want to go through this method for compatibility with
                // existing applications that may have overridden it.
                mParent.startActivityFromChild(this, intent, requestCode);
            }
        }
    }
startActivity ForResult()メソッドでは、まず、そのActivityが親Activity、すなわちmParentによって起動されているかどうかを判断します.彼が最初のActivityであれば、InstrumentationのexecStartActivity()メソッドが呼び出されます.次に、このメソッドのソースコードを見てみましょう.
   public ActivityResult execStartActivity(
            Context who, IBinder contextThread, IBinder token, Activity target,
            Intent intent, int requestCode, Bundle options) {
        IApplicationThread whoThread = (IApplicationThread) contextThread;
        Uri referrer = target != null ? target.onProvideReferrer() : null;
        if (referrer != null) {
            intent.putExtra(Intent.EXTRA_REFERRER, referrer);
        }
        if (mActivityMonitors != null) {
            synchronized (mSync) {
                final int N = mActivityMonitors.size();
                for (int i=0; i= 0 ? am.getResult() : null;
                        }
                        break;
                    }
                }
            }
        }
        try {
            intent.migrateExtraStreamToClipData();
            intent.prepareToLeaveProcess(who);
            int result = ActivityManagerNative.getDefault()
                .startActivity(whoThread, who.getBasePackageName(), intent,
                        intent.resolveTypeIfNeeded(who.getContentResolver()),
                        token, target != null ? target.mEmbeddedID : null,
                        requestCode, 0, null, options);
            checkStartActivityResult(result, intent);
        } catch (RemoteException e) {
            throw new RuntimeException("Failure from system", e);
        }
        return null;
    }
ソースコードからこの方法の核心コードはActivityManagerNativeを呼び出したことがわかる.getDefault().startActivity()でgetDefault()のソースコードを見てみましょう
  static public IActivityManager getDefault() {
        return gDefault.get();
    }
    
    private static final Singleton gDefault = new Singleton() {
        protected IActivityManager create() {
            IBinder b = ServiceManager.getService("activity");
            if (false) {
                Log.v("ActivityManager", "default service binder = " + b);
            }
            IActivityManager am = asInterface(b);
            if (false) {
                Log.v("ActivityManager", "default service = " + am);
            }
            return am;
        }
    };
上記のコードを見て、IActivityManagerはasInterface()メソッドを呼び出し、そのソースコード:
    static public IActivityManager asInterface(IBinder obj) {
        if (obj == null) {
            return null;
        }
        IActivityManager in =
            (IActivityManager)obj.queryLocalInterface(descriptor);
        if (in != null) {
            return in;
        }

        return new ActivityManagerProxy(obj);
    }

 public ActivityManagerProxy(IBinder remote)
    {
        mRemote = remote;
    }

    public IBinder asBinder()
    {
        return mRemote;
    }

    public int startActivity(IApplicationThread caller, String callingPackage, Intent intent,
            String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle options) throws RemoteException {
        Parcel data = Parcel.obtain();
        Parcel reply = Parcel.obtain();
        data.writeInterfaceToken(IActivityManager.descriptor);
        data.writeStrongBinder(caller != null ? caller.asBinder() : null);
        data.writeString(callingPackage);
        intent.writeToParcel(data, 0);
        data.writeString(resolvedType);
        data.writeStrongBinder(resultTo);
        data.writeString(resultWho);
        data.writeInt(requestCode);
        data.writeInt(startFlags);
        if (profilerInfo != null) {
            data.writeInt(1);
            profilerInfo.writeToParcel(data, Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
        } else {
            data.writeInt(0);
        }
        if (options != null) {
            data.writeInt(1);
            options.writeToParcel(data, 0);
        } else {
            data.writeInt(0);
        }
        mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);
        reply.readException();
        int result = reply.readInt();
        reply.recycle();
        data.recycle();
        return result;
    }
asInterfaceがActivityManagerProxyオブジェクト、すなわちActivityManagerNativeを返すことがわかる.getDefault()はActivity Management Proxyオブジェクトを返します.以前のBInderメカニズムの記事では、Proxyがクライアントで実行されていることがわかります.クライアントはProxyクラスにパラメータを書き込むことで、ProxyがBinderを介してサービス側をリモートで呼び出す具体的な方法を知っています.そのため、Activity Management Proxyを借りてActivity Management Serviceを呼び出す方法Activity Management ServiceはActivity Management Nativeから継承されます.ActivityManagerNativeはBinderから継承され、IActivityManagerというBinderインタフェースを実現しているため、ActivityManagerServiceもBinderであり、IActivityManagerの具体的な実装である.
次に、AMSでActivityを起動します.ソースコードは次のとおりです.
    @Override
    public final int startActivity(IApplicationThread caller, String callingPackage,
            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
        return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
                resultWho, requestCode, startFlags, profilerInfo, bOptions,
                UserHandle.getCallingUserId());
    }
    @Override
    public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId) {
        enforceNotIsolatedCaller("startActivity");
        userId = mUserController.handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(),
                userId, false, ALLOW_FULL_ONLY, "startActivity", null);
        // TODO: Switch to user app stacks here.
        return mActivityStarter.startActivityMayWait(caller, -1, callingPackage, intent,
                resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
                profilerInfo, null, null, bOptions, false, userId, null, null);
    }
startActivityではstartActivity AssUserメソッドが直接呼び出すが、startActivity AssUserではmStackSupervisorが呼び出される.startActivity MayWaitメソッド.
startActivityMayWait関数のソースコードは長く、簡単にまとめると次のようになります.
startActivityMayWait()->startActivityLocked()->startActivityUncheckedLocked()->startSpecificActivityLocked()->startActivityLocked()->resumeTopActivitiesLocked()->resumeTopActivityLocked().
一連の呼び出しの後、最終的にstartPausingLockedメソッドに到達し、ActivityのonPauseメソッドを実行し、現在のActivityを終了します.
final boolean startPausingLocked(boolean userLeaving, boolean uiSleeping, boolean resuming,boolean dontWait) {
    ...
    if (prev.app != null && prev.app.thread != null) {
        if (DEBUG_PAUSE) Slog.v(TAG_PAUSE, "Enqueueing pending pause: " + prev);
        try {
            EventLog.writeEvent(EventLogTags.AM_PAUSE_ACTIVITY,
                    prev.userId, System.identityHashCode(prev),
                    prev.shortComponentName);
            mService.updateUsageStats(prev, false);
            prev.app.thread.schedulePauseActivity(prev.appToken, prev.finishing,
                    userLeaving, prev.configChangeFlags, dontWait);
        } catch (Exception e) {
            // Ignore exception, if process died other code will cleanup.
            Slog.w(TAG, "Exception thrown during pause", e);
            mPausingActivity = null;
            mLastPausedActivity = null;
            mLastNoHistoryActivity = null;
        }
    } else {
        mPausingActivity = null;
        mLastPausedActivity = null;
        mLastNoHistoryActivity = null;
    }
    ...
}
このコードはappのため非常に重要です.threadのタイプはIApplicationThreadであり、その具体的な実装はActivity ThreadのApplicationThreadクラスであり、ApplicationThreadはActivity Threadの内部クラスであり、IApplicationThreadを継承し、Binderオブジェクトであるため、Appcationはゲスト側であり、Activity Threadはサービス側であり、これまでActivityの呼び出しはActivity Threadに来ていた.
Activity Threadで現在のActivityを削除するには、schedulePauseActivityを呼び出してpause操作を実行します.
public final void schedulePauseActivity(IBinder token, boolean finished,
                boolean userLeaving, int configChanges, boolean dontReport) {
            int seq = getLifecycleSeq();
            if (DEBUG_ORDER) Slog.d(TAG, "pauseActivity " + ActivityThread.this
                    + " operation received seq: " + seq);
            sendMessage(
                    finished ? H.PAUSE_ACTIVITY_FINISHING : H.PAUSE_ACTIVITY,
                    token,
                    (userLeaving ? USER_LEAVING : 0) | (dontReport ? DONT_REPORT : 0),
                    configChanges,
                    seq);
        }
schedulePauseActivityではhandlerによってメッセージが送信され、メッセージタイプはPAUSE_であることがわかります.ACTIVITY_FINISHING
   private void handlePauseActivity(IBinder token, boolean finished,
            boolean userLeaving, int configChanges, boolean dontReport, int seq) {
        ActivityClientRecord r = mActivities.get(token);
        if (DEBUG_ORDER) Slog.d(TAG, "handlePauseActivity " + r + ", seq: " + seq);
        if (!checkAndUpdateLifecycleSeq(seq, r, "pauseActivity")) {
            return;
        }
        if (r != null) {
            //Slog.v(TAG, "userLeaving=" + userLeaving + " handling pause of " + r);
            if (userLeaving) {
                performUserLeavingActivity(r);
            }

            r.activity.mConfigChangeFlags |= configChanges;
            performPauseActivity(token, finished, r.isPreHoneycomb(), "handlePauseActivity");

            // Make sure any pending writes are now committed.
            if (r.isPreHoneycomb()) {
                QueuedWork.waitToFinish();
            }

            // Tell the activity manager we have paused.
            if (!dontReport) {
                try {
                    ActivityManagerNative.getDefault().activityPaused(token);
                } catch (RemoteException ex) {
                    throw ex.rethrowFromSystemServer();
                }
            }
            mSomeActivitiesChanged = true;
        }
    }
新しいActivityを起動します.startSpecificActivity Lockedメソッドでは、Activityを呼び出すpauseメソッドと同様に、Activityを起動するメッセージをHandlerメカニズムで送信し、そのメッセージを処理して最後にActivityを起動します.performLaunchActivityメソッドを呼び出します.
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
        // System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")");

        ActivityInfo aInfo = r.activityInfo;
        if (r.packageInfo == null) {
            r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,
                    Context.CONTEXT_INCLUDE_CODE);
        }

        ComponentName component = r.intent.getComponent();
        if (component == null) {
            component = r.intent.resolveActivity(
                mInitialApplication.getPackageManager());
            r.intent.setComponent(component);
        }

        if (r.activityInfo.targetActivity != null) {
            component = new ComponentName(r.activityInfo.packageName,
                    r.activityInfo.targetActivity);
        }

        Activity activity = null;
        try {
            java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
            activity = mInstrumentation.newActivity(
                    cl, component.getClassName(), r.intent);
            StrictMode.incrementExpectedActivityCount(activity.getClass());
            r.intent.setExtrasClassLoader(cl);
            r.intent.prepareToEnterProcess();
            if (r.state != null) {
                r.state.setClassLoader(cl);
            }
        } catch (Exception e) {
            if (!mInstrumentation.onException(activity, e)) {
                throw new RuntimeException(
                    "Unable to instantiate activity " + component
                    + ": " + e.toString(), e);
            }
        }

        try {
            Application app = r.packageInfo.makeApplication(false, mInstrumentation);

            if (localLOGV) Slog.v(TAG, "Performing launch of " + r);
            if (localLOGV) Slog.v(
                    TAG, r + ": app=" + app
                    + ", appName=" + app.getPackageName()
                    + ", pkg=" + r.packageInfo.getPackageName()
                    + ", comp=" + r.intent.getComponent().toShortString()
                    + ", dir=" + r.packageInfo.getAppDir());

            if (activity != null) {
                Context appContext = createBaseContextForActivity(r, activity);
                CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
                Configuration config = new Configuration(mCompatConfiguration);
                if (r.overrideConfig != null) {
                    config.updateFrom(r.overrideConfig);
                }
                if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "
                        + r.activityInfo.name + " with config " + config);
                Window window = null;
                if (r.mPendingRemoveWindow != null && r.mPreserveWindow) {
                    window = r.mPendingRemoveWindow;
                    r.mPendingRemoveWindow = null;
                    r.mPendingRemoveWindowManager = null;
                }
                activity.attach(appContext, this, getInstrumentation(), r.token,
                        r.ident, app, r.intent, r.activityInfo, title, r.parent,
                        r.embeddedID, r.lastNonConfigurationInstances, config,
                        r.referrer, r.voiceInteractor, window);

                if (customIntent != null) {
                    activity.mIntent = customIntent;
                }
                r.lastNonConfigurationInstances = null;
                activity.mStartedActivity = false;
                int theme = r.activityInfo.getThemeResource();
                if (theme != 0) {
                    activity.setTheme(theme);
                }

                activity.mCalled = false;
                if (r.isPersistable()) {
                    mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
                } else {
                    mInstrumentation.callActivityOnCreate(activity, r.state);
                }
                if (!activity.mCalled) {
                    throw new SuperNotCalledException(
                        "Activity " + r.intent.getComponent().toShortString() +
                        " did not call through to super.onCreate()");
                }
                r.activity = activity;
                r.stopped = true;
                if (!r.activity.mFinished) {
                    activity.performStart();
                    r.stopped = false;
                }
                if (!r.activity.mFinished) {
                    if (r.isPersistable()) {
                        if (r.state != null || r.persistentState != null) {
                            mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state,
                                    r.persistentState);
                        }
                    } else if (r.state != null) {
                        mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
                    }
                }
                if (!r.activity.mFinished) {
                    activity.mCalled = false;
                    if (r.isPersistable()) {
                        mInstrumentation.callActivityOnPostCreate(activity, r.state,
                                r.persistentState);
                    } else {
                        mInstrumentation.callActivityOnPostCreate(activity, r.state);
                    }
                    if (!activity.mCalled) {
                        throw new SuperNotCalledException(
                            "Activity " + r.intent.getComponent().toShortString() +
                            " did not call through to super.onPostCreate()");
                    }
                }
            }
            r.paused = true;

            mActivities.put(r.token, r);

        } catch (SuperNotCalledException e) {
            throw e;

        } catch (Exception e) {
            if (!mInstrumentation.onException(activity, e)) {
                throw new RuntimeException(
                    "Unable to start activity " + component
                    + ": " + e.toString(), e);
            }
        }

        return activity;
    }
最終的なActivityオブジェクトがやっと作成されたことがわかります.
参考『Android開発芸術探索』著者ブログ