技術標籤：Launcher

一.開始

Launcher中點選應用圖示啟動Activity，其開始方法是

public boolean startActivitySafely(View v, Intent intent, ItemInfo item) {
        if (mIsSafeModeEnabled && !Utilities.isSystemApp(this, intent)) {
            Toast.makeText(this, R.string.safemode_shortcut_error, Toast.LENGTH_SHORT).show();
            return false;
        }
        boolean useLaunchAnimation = (v != null) &&
                !intent.hasExtra(INTENT_EXTRA_IGNORE_LAUNCH_ANIMATION);
        Bundle optsBundle = useLaunchAnimation ? getActivityLaunchOptions(v) : null;

        UserHandle user = item == null ? null : item.user;

        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        if (v != null) {
            intent.setSourceBounds(getViewBounds(v));
        }
        try {
            if (Utilities.ATLEAST_MARSHMALLOW
                    && (item instanceof ShortcutInfo)
                    && (item.itemType == Favorites.ITEM_TYPE_SHORTCUT
                    || item.itemType == Favorites.ITEM_TYPE_DEEP_SHORTCUT)
                    && !((ShortcutInfo) item).isPromise()) {
                // Shortcuts need some special checks due to legacy reasons.
                startShortcutIntentSafely(intent, optsBundle, item);
            } else if (user == null || user.equals(Process.myUserHandle())) {
                // Could be launching some bookkeeping activity
                startActivity(intent, optsBundle);
            } else {
                LauncherAppsCompat.getInstance(this).startActivityForProfile(
                        intent.getComponent(), user, intent.getSourceBounds(), optsBundle);
            }
            return true;
        } catch (ActivityNotFoundException | SecurityException e) {
            Toast.makeText(this, R.string.activity_not_found, Toast.LENGTH_SHORT).show();
            LogUtils.e("Unable to launch. tag=" + item + " intent=" + intent);
        }
        return false;
    }
 

最終，它會走startActivity(intent, optsBundle)方法，我們繼續看下實現

 @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);
        }
    }
 

呼叫startActivityForResult，看其實現

 public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
            @Nullable Bundle options) {
        if (mParent == null) {
            options = transferSpringboardActivityOptions(options);
            Instrumentation.ActivityResult ar =
                mInstrumentation.execStartActivity(
                    this, mMainThread.getApplicationThread(), mToken, this,
                    intent, requestCode, options);
            if (ar != null) {
                mMainThread.sendActivityResult(
                    mToken, mEmbeddedID, requestCode, ar.getResultCode(),
                    ar.getResultData());
            }
            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);
            }
        }
    }
 

Instrumentation.ActivityResult ar =mInstrumentation.execStartActivity(this, mMainThread.getApplicationThread(), mToken, this,intent, requestCode, options)，Activity的啟動交給了Instrumentation實現，每個程序都會存在一個Instrumentation，它對於Activity生命週期的管理至關重要，看下其實現

 public ActivityResult execStartActivity(
            Context who, IBinder contextThread, IBinder token, Activity target,
            Intent intent, int requestCode, Bundle options) {
    ...
 try {
            intent.migrateExtraStreamToClipData(who);
            intent.prepareToLeaveProcess(who);
            int result = ActivityTaskManager.getService().startActivity(whoThread,
                    who.getBasePackageName(), who.getAttributionTag(), 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);
        }
}

我們看到ActivityTaskManager.getService()執行startActivity，看下其實現

   /** @hide */
    public static IActivityTaskManager getService() {
        return IActivityTaskManagerSingleton.get();
    }

    @UnsupportedAppUsage(trackingBug = 129726065)
    private static final Singleton<IActivityTaskManager> IActivityTaskManagerSingleton =
            new Singleton<IActivityTaskManager>() {
                @Override
                protected IActivityTaskManager create() {
                    final IBinder b = ServiceManager.getService(Context.ACTIVITY_TASK_SERVICE);
                    return IActivityTaskManager.Stub.asInterface(b);
                }
            };

這裡，我們看到IActivityTaskManager實際上是AMS返回的代理類，也就是startActivity真正實現是AMS中實現的。

二.ActivityManagerService啟動應用

看下AMS的startActivity實現

 public int startActivity(IApplicationThread caller, String callingPackage,
            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
        return mActivityTaskManager.startActivity(caller, callingPackage, null, intent,
                resolvedType, resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions);
    }

mActivityTaskManager為ActivityTaskManagerService，其實現是

   @Override
    public final int startActivity(IApplicationThread caller, String callingPackage,
            String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,
            String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,
            Bundle bOptions) {
        return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
                resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions,
                UserHandle.getCallingUserId());
    }

  @Override
    public int startActivityAsUser(IApplicationThread caller, String callingPackage,
            String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,
            String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,
            Bundle bOptions, int userId) {
        return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
                resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions, userId,
                true /*validateIncomingUser*/);
    }

private int startActivityAsUser(IApplicationThread caller, String callingPackage,
            @Nullable String callingFeatureId, Intent intent, String resolvedType,
            IBinder resultTo, String resultWho, int requestCode, int startFlags,
            ProfilerInfo profilerInfo, Bundle bOptions, int userId, boolean validateIncomingUser) {
        assertPackageMatchesCallingUid(callingPackage);
        enforceNotIsolatedCaller("startActivityAsUser");

        userId = getActivityStartController().checkTargetUser(userId, validateIncomingUser,
                Binder.getCallingPid(), Binder.getCallingUid(), "startActivityAsUser");

        // TODO: Switch to user app stacks here.
        return getActivityStartController().obtainStarter(intent, "startActivityAsUser")
                .setCaller(caller)
                .setCallingPackage(callingPackage)
                .setCallingFeatureId(callingFeatureId)
                .setResolvedType(resolvedType)
                .setResultTo(resultTo)
                .setResultWho(resultWho)
                .setRequestCode(requestCode)
                .setStartFlags(startFlags)
                .setProfilerInfo(profilerInfo)
                .setActivityOptions(bOptions)
                .setUserId(userId)
                .execute();

    }

我們看下obtainStarter的實現

 ActivityStarter obtainStarter(Intent intent, String reason) {
        return mFactory.obtain().setIntent(intent).setReason(reason);
    }

進入execute檢視

 int execute() {
        ...
        int res;
        synchronized (mService.mGlobalLock) {
            final boolean globalConfigWillChange = mRequest.globalConfig != null
                    && mService.getGlobalConfiguration().diff(mRequest.globalConfig) != 0;
            final ActivityStack stack = mRootWindowContainer.getTopDisplayFocusedStack();
            if (stack != null) {
                stack.mConfigWillChange = globalConfigWillChange;
            }
            if (DEBUG_CONFIGURATION) {
                Slog.v(TAG_CONFIGURATION, "Starting activity when config will change = "
                        + globalConfigWillChange);
            }

            final long origId = Binder.clearCallingIdentity();

            res = resolveToHeavyWeightSwitcherIfNeeded();
            if (res != START_SUCCESS) {
                return res;
            }
            res = executeRequest(mRequest);
        }

    }

最終會執行res = executeRequest(mRequest)，進一步檢視

private int executeRequest(Request request) {
        ...
        mService.onStartActivitySetDidAppSwitch();
        mController.doPendingActivityLaunches(false);

        mLastStartActivityResult = startActivityUnchecked(r, sourceRecord, voiceSession,
                request.voiceInteractor, startFlags, true /* doResume */, checkedOptions, inTask,
                restrictedBgActivity, intentGrants);

        if (request.outActivity != null) {
            request.outActivity[0] = mLastStartActivityRecord;
        }

        return mLastStartActivityResult;
    }

邏輯很多，但最終會執行startActivityUnchecked方法，進一步分析

  private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
                IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
                int startFlags, boolean doResume, ActivityOptions options, Task inTask,
                boolean restrictedBgActivity, NeededUriGrants intentGrants) {
        int result = START_CANCELED;
        final ActivityStack startedActivityStack;
        try {
            mService.deferWindowLayout();
            Trace.traceBegin(Trace.TRACE_TAG_WINDOW_MANAGER, "startActivityInner");
            result = startActivityInner(r, sourceRecord, voiceSession, voiceInteractor,
                    startFlags, doResume, options, inTask, restrictedBgActivity, intentGrants);
        } finally {
            Trace.traceEnd(Trace.TRACE_TAG_WINDOW_MANAGER);
            startedActivityStack = handleStartResult(r, result);
            mService.continueWindowLayout();
        }

        postStartActivityProcessing(r, result, startedActivityStack);

        return result;
    }

繼續執行startActivityInner方法

int startActivityInner(final ActivityRecord r, ActivityRecord sourceRecord,
            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
            int startFlags, boolean doResume, ActivityOptions options, Task inTask,
            boolean restrictedBgActivity, NeededUriGrants intentGrants) {
        setInitialState(r, options, inTask, doResume, startFlags, sourceRecord, voiceSession,
                voiceInteractor, restrictedBgActivity);
    ...
    mRootWindowContainer.resumeFocusedStacksTopActivities(
                       mTargetStack, mStartActivity, mOptions);

}}

最終執行mRootWindowContainer.resumeFocusedStacksTopActivities( mTargetStack, mStartActivity, mOptions);mRootWindowContainer為RootWindowContainer，看其實現

 boolean resumeFocusedStacksTopActivities() {
        return resumeFocusedStacksTopActivities(null, null, null);
    }

  boolean resumeFocusedStacksTopActivities(
            ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
        if (!mStackSupervisor.readyToResume()) {
            return false;
        }
        boolean result = false;
        if (targetStack != null && (targetStack.isTopStackInDisplayArea()
                || getTopDisplayFocusedStack() == targetStack)) {
            result = targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
        }
        return result;
    }

targetStack為ActivityStack，實現resumeTopActivityUncheckedLocked，看其實現

 boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
        if (mInResumeTopActivity) {
            // Don't even start recursing.
            return false;
        }
        boolean result = false;
        try {
            // Protect against recursion.
            mInResumeTopActivity = true;
            result = resumeTopActivityInnerLocked(prev, options);
            ...
        } finally {
            mInResumeTopActivity = false;
        }
        return result;
    }

 private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
    ...
        mStackSupervisor.startSpecificActivity(next, true, true);
    ...
    }

mStatckSupervisor為ActivityStackSupervisor，看其實現

   void startSpecificActivity(ActivityRecord r, boolean andResume, boolean checkConfig) {
        // Is this activity's application already running?
        final WindowProcessController wpc =
                mService.getProcessController(r.processName, r.info.applicationInfo.uid);

        boolean knownToBeDead = false;
        if (wpc != null && wpc.hasThread()) {
            try {
                realStartActivityLocked(r, wpc, andResume, checkConfig);
                return;
            } catch (RemoteException e) {
                Slog.w(TAG, "Exception when starting activity "
                        + r.intent.getComponent().flattenToShortString(), e);
            }

            // If a dead object exception was thrown -- fall through to
            // restart the application.
            knownToBeDead = true;
        }

        r.notifyUnknownVisibilityLaunchedForKeyguardTransition();

        final boolean isTop = andResume && r.isTopRunningActivity();
        mService.startProcessAsync(r, knownToBeDead, isTop, isTop ? "top-activity" : "activity");
    }

這個方法是個關鍵點，mService.getProcessController獲取點wpc為程序管理者，如果wpc.hasThread()為true，即已生成了程序，則直接呼叫realStartActivityLocked啟動Activity，否則先執行mService.startProcessAsync來生成程序，因為是Launcher啟動應用，所以先執行生成程序操作。