Android系统启动流程-桌面程序的启动

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在SystemServer启动“Other”类型服务的时候,最后阶段会执行ActivityManagerService的systemReady()方法,这里就是启动桌面程序的入口.


        mActivityManagerService.systemReady(() -> {

            traceBeginAndSlog("StartSystemUI");
            try {
                startSystemUi(context, windowManagerF);
            } catch (Throwable e) {
                reportWtf("starting System UI", e);
            }
            traceEnd();

            // Wait for all packages to be prepared
            mPackageManagerService.waitForAppDataPrepared();

            // It is now okay to let the various system services start their
            // third party code...
            traceBeginAndSlog("PhaseThirdPartyAppsCanStart");
            mSystemServiceManager.startBootPhase(
                    SystemService.PHASE_THIRD_PARTY_APPS_CAN_START);
            traceEnd();

        }, BOOT_TIMINGS_TRACE_LOG);

在ActivityManagerService中的systemReady()方法中有这么一段:


mAtmInternal.startHomeOnAllDisplays(currentUserId, "systemReady");

在ActivityTaskManagerService中有实现:


        @Override
        public boolean startHomeOnAllDisplays(int userId, String reason) {
            synchronized (mGlobalLock) {
                return mRootActivityContainer.startHomeOnAllDisplays(userId, reason);
            }
        }

最终会执行到RootActivityContainer中:


    boolean startHomeOnAllDisplays(int userId, String reason) {
        boolean homeStarted = false;
        for (int i = mActivityDisplays.size() - 1; i >= 0; i--) {
            final int displayId = mActivityDisplays.get(i).mDisplayId;
            homeStarted |= startHomeOnDisplay(userId, reason, displayId);
        }
        return homeStarted;
    }

    boolean startHomeOnDisplay(int userId, String reason, int displayId, boolean allowInstrumenting,
            boolean fromHomeKey) {
        // Fallback to top focused display if the displayId is invalid.
        if (displayId == INVALID_DISPLAY) {
            displayId = getTopDisplayFocusedStack().mDisplayId;
        }

        Intent homeIntent = null;
        ActivityInfo aInfo = null;
        if (displayId == DEFAULT_DISPLAY) {
            // 获取Home Intent
            homeIntent = mService.getHomeIntent();
            aInfo = resolveHomeActivity(userId, homeIntent);
        } else if (shouldPlaceSecondaryHomeOnDisplay(displayId)) {
            Pair<ActivityInfo, Intent> info = resolveSecondaryHomeActivity(userId, displayId);
            aInfo = info.first;
            homeIntent = info.second;
        }
        if (aInfo == null || homeIntent == null) {
            return false;
        }

        if (!canStartHomeOnDisplay(aInfo, displayId, allowInstrumenting)) {
            return false;
        }

        // Updates the home component of the intent.
        homeIntent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));
        homeIntent.setFlags(homeIntent.getFlags() | FLAG_ACTIVITY_NEW_TASK);
        // Updates the extra information of the intent.
        if (fromHomeKey) {
            homeIntent.putExtra(WindowManagerPolicy.EXTRA_FROM_HOME_KEY, true);
        }
        // Update the reason for ANR debugging to verify if the user activity is the one that
        // actually launched.
        final String myReason = reason + ":" + userId + ":" + UserHandle.getUserId(
                aInfo.applicationInfo.uid) + ":" + displayId;
        mService.getActivityStartController().startHomeActivity(homeIntent, aInfo, myReason,
                displayId);
        return true;
    }

这里会找到桌面程序的Intent:


    Intent getHomeIntent() {
        Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);
        intent.setComponent(mTopComponent);
        intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);
        if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
            intent.addCategory(Intent.CATEGORY_HOME);
        }
        return intent;
    }

剩下的就是启动桌面程序了.

Launcher的启动流程代码写的不是一般的混乱,启动Launcher的时候会有好几次的防护,针对Launcher启动崩溃也做了相应的处理.
没有经过debug,可能存在其他的路径启动Launcher,后续如果还有兴趣的话再补充.