前言

在之前我們學(xué)習(xí)了init進(jìn)程琼腔、Zygote進(jìn)程和SyetemServer進(jìn)程的啟動(dòng)過(guò)程，我們知道SystemServer進(jìn)程主要用于啟動(dòng)系統(tǒng)的各種服務(wù)尸诽，二者其中就包含了負(fù)責(zé)啟動(dòng)Launcher的服務(wù)盯另，LauncherAppService性含，本篇我們將一起學(xué)習(xí)Launcher相關(guān)的知識(shí)。

Launcher概述

Launcher程序就是我們平時(shí)看到的桌面程序鸳惯，它其實(shí)也是一個(gè)Android應(yīng)用程序商蕴，只不過(guò)這個(gè)應(yīng)用程序是系統(tǒng)默認(rèn)第一個(gè)啟動(dòng)的應(yīng)用程序，Android系統(tǒng)啟動(dòng)的最后一步就是啟動(dòng)Launcher程序芝发，應(yīng)用程序Launcher在啟動(dòng)過(guò)程中會(huì)請(qǐng)求PackageManagerService返回系統(tǒng)中已經(jīng)安裝的應(yīng)用程序的信息绪商，并將這些信息封裝成一個(gè)快捷圖標(biāo)列表顯示在系統(tǒng)屏幕上，這樣用戶可以通過(guò)點(diǎn)擊這些快捷圖標(biāo)來(lái)啟動(dòng)相應(yīng)的應(yīng)用程序格郁。

Launcher啟動(dòng)流程

SystemServer進(jìn)程的啟動(dòng)過(guò)程中會(huì)調(diào)用其main靜態(tài)方法，開(kāi)始執(zhí)行整個(gè)SystemServer的啟動(dòng)流程独悴，在其中通過(guò)調(diào)用三個(gè)內(nèi)部方法分別啟動(dòng)boot service例书、core service和other service。在調(diào)用startOtherService方法中就會(huì)通過(guò)調(diào)用mActivityManagerService.systemReady()方法刻炒，而這個(gè)ActivityManagerService的systemReady函數(shù)就是啟動(dòng)Launcher的入口决采。 frameworks/base/services/Java/com/android/server/SystemServer.java

 private void startOtherServices() {
 ...
  mActivityManagerService.systemReady(new Runnable() {
            @Override
            public void run() {
                Slog.i(TAG, "Making services ready");
                mSystemServiceManager.startBootPhase(
                        SystemService.PHASE_ACTIVITY_MANAGER_READY);

...
}
...
}

可以發(fā)現(xiàn)這個(gè)方法傳遞了一個(gè)Runnable參數(shù)，里面執(zhí)行了各種其他服務(wù)的systemReady方法落蝙，這里不是我們關(guān)注的重點(diǎn)织狐，我們看一下在ActivityManagerService中systemReady方法的具體實(shí)現(xiàn) frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

public void systemReady(final Runnable goingCallback) {
        ...
        // Start up initial activity.
        mBooting = true;
        startHomeActivityLocked(mCurrentUserId, "systemReady");
        ...
    }

重點(diǎn)是在這個(gè)方法體中調(diào)用了startHomeActivityLocked方法暂幼，看其名字就是說(shuō)開(kāi)始執(zhí)行啟動(dòng)homeActivity的操作

boolean startHomeActivityLocked(int userId, String reason) {
        if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL
                && mTopAction == null) {//1
            return false;
        }
        Intent intent = getHomeIntent();//2
        ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);
        if (aInfo != null) {
            intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));
            aInfo = new ActivityInfo(aInfo);
            aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);
            ProcessRecord app = getProcessRecordLocked(aInfo.processName,
                    aInfo.applicationInfo.uid, true);
            if (app == null || app.instrumentationClass == null) {//3
                intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);
                mActivityStarter.startHomeActivityLocked(intent, aInfo, reason);//4
            }
        } else {
            Slog.wtf(TAG, "No home screen found for " + intent, new Throwable());
        }

        return true;
    }

注釋1處的mFactoryTest代表系統(tǒng)的運(yùn)行模式筏勒，系統(tǒng)的運(yùn)行模式分為三種，分別是非工廠模式旺嬉、低級(jí)工廠模式和高級(jí)工廠模式管行，mTopAction則用來(lái)描述第一個(gè)被啟動(dòng)Activity組件的Action，它的值為Intent.ACTION_MAIN邪媳。因此注釋1的代碼意思就是mFactoryTest為FactoryTest.FACTORY_TEST_LOW_LEVEL（低級(jí)工廠模式）并且mTopAction=null時(shí)捐顷，直接返回false，然后是調(diào)用getHomeIntent()方法

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

getHomeIntent函數(shù)中創(chuàng)建了Intent雨效，并將mTopAction和mTopData傳入迅涮。mTopAction的值為Intent.ACTION_MAIN，并且如果系統(tǒng)運(yùn)行模式不是低級(jí)工廠模式則將intent的Category設(shè)置為Intent.CATEGORY_HOME徽龟。Launcher的Intent對(duì)象中添加了Intent.CATEGORY_HOME常量叮姑，這個(gè)其實(shí)是一個(gè)launcher的標(biāo)志，一般系統(tǒng)的啟動(dòng)頁(yè)面Activity都會(huì)在androidmanifest.xml中配置這個(gè)標(biāo)志。

我們?cè)倩氐紸ctivityManagerService的startHomeActivityLocked函數(shù)传透，假設(shè)系統(tǒng)的運(yùn)行模式不是低級(jí)工廠模式耘沼，在注釋3處判斷符合Action為Intent.ACTION_MAIN，Category為Intent.CATEGORY_HOME的應(yīng)用程序是否已經(jīng)啟動(dòng)朱盐，如果沒(méi)啟動(dòng)則調(diào)用注釋4的方法啟動(dòng)該應(yīng)用程序群嗤。

startHomeActivityLocked方法中，經(jīng)過(guò)一系列的判斷邏輯之后最后調(diào)用了mStackSupervisor.startHomeActivity方法

void startHomeActivity(Intent intent, ActivityInfo aInfo, String reason) {
        moveHomeStackTaskToTop(HOME_ACTIVITY_TYPE, reason);
        startActivityLocked(null /* caller */, intent, null /* resolvedType */, aInfo,
                null /* voiceSession */, null /* voiceInteractor */, null /* resultTo */,
                null /* resultWho */, 0 /* requestCode */, 0 /* callingPid */, 0 /* callingUid */,
                null /* callingPackage */, 0 /* realCallingPid */, 0 /* realCallingUid */,
                0 /* startFlags */, null /* options */, false /* ignoreTargetSecurity */,
                false /* componentSpecified */,
                null /* outActivity */, null /* container */,  null /* inTask */);
        if (inResumeTopActivity) {
            // If we are in resume section already, home activity will be initialized, but not
            // resumed (to avoid recursive resume) and will stay that way until something pokes it
            // again. We need to schedule another resume.
            scheduleResumeTopActivities();
        }
    }

發(fā)現(xiàn)其調(diào)用的是scheduleResumeTopActivities()方法兵琳，這個(gè)方法中就是Activity的啟動(dòng)流程的邏輯了狂秘，此處不展開(kāi)。

Launcher啟動(dòng)的Intent是一個(gè)隱士的Intent闰围，所以我們會(huì)啟動(dòng)在androidmanifest.xml中配置了相同catogory的activity赃绊，android M中配置的這個(gè)catogory就是LauncherActivity。

LauncherActivity繼承與ListActivity羡榴，我們看一下其Layout布局文件：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >

    <ListView
        android:id="@android:id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />

    <TextView
        android:id="@android:id/empty"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="@string/activity_list_empty"
        android:visibility="gone"
        android:textAppearance="?android:attr/textAppearanceMedium"
        />

</FrameLayout>

可以看到我們現(xiàn)實(shí)的桌面其實(shí)就是一個(gè)ListView控件碧查，通過(guò)intent,應(yīng)用程序Launcher就會(huì)被啟動(dòng)起來(lái)，并執(zhí)行它的onCreate函數(shù)校仑。

Launcher中應(yīng)用圖標(biāo)顯示流程

packages/apps/Launcher3/src/com/android/launcher3/Launcher.java

  @Override
    protected void onCreate(Bundle savedInstanceState) {
       ...
        LauncherAppState app = LauncherAppState.getInstance();//1
        mDeviceProfile = getResources().getConfiguration().orientation
                == Configuration.ORIENTATION_LANDSCAPE ?
                app.getInvariantDeviceProfile().landscapeProfile
                : app.getInvariantDeviceProfile().portraitProfile;

        mSharedPrefs = Utilities.getPrefs(this);
        mIsSafeModeEnabled = getPackageManager().isSafeMode();
        mModel = app.setLauncher(this);//2
        ....
        if (!mRestoring) {
            if (DISABLE_SYNCHRONOUS_BINDING_CURRENT_PAGE) {
                mModel.startLoader(PagedView.INVALID_RESTORE_PAGE);//2
            } else {
                mModel.startLoader(mWorkspace.getRestorePage());
            }
        }
...
    }

注釋1處獲取LauncherAppState的實(shí)例并在注釋2處調(diào)用它的setLauncher函數(shù)并將Launcher對(duì)象傳入 packages/apps/Launcher3/src/com/android/launcher3/LauncherAppState.java

 LauncherModel setLauncher(Launcher launcher) {
        getLauncherProvider().setLauncherProviderChangeListener(launcher);
        mModel.initialize(launcher);//1
        mAccessibilityDelegate = ((launcher != null) && Utilities.ATLEAST_LOLLIPOP) ?
            new LauncherAccessibilityDelegate(launcher) : null;
        return mModel;
    }

注釋1處會(huì)調(diào)用LauncherModel的initialize函數(shù)：

public void initialize(Callbacks callbacks) {
    synchronized (mLock) {
        unbindItemInfosAndClearQueuedBindRunnables();
        mCallbacks = new WeakReference<Callbacks>(callbacks);
    }
}

在initialize函數(shù)中會(huì)將Callbacks忠售，也就是傳入的Launcher 封裝成一個(gè)弱引用對(duì)象。因此我們得知mCallbacks變量指的就是封裝成弱引用對(duì)象的Launcher迄沫，這個(gè)mCallbacks后文會(huì)用到它稻扬。 再回到Launcher的onCreate函數(shù)，在注釋2處調(diào)用了LauncherModel的startLoader函數(shù)：

packages/apps/Launcher3/src/com/android/launcher3/LauncherModel.java

...
 @Thunk static final HandlerThread sWorkerThread = new HandlerThread("launcher-loader");//1
    static {
        sWorkerThread.start();
    }
    @Thunk static final Handler sWorker = new Handler(sWorkerThread.getLooper());//2
...
   public void startLoader(int synchronousBindPage, int loadFlags) {s
        InstallShortcutReceiver.enableInstallQueue();
        synchronized (mLock) {
            synchronized (mDeferredBindRunnables) {
                mDeferredBindRunnables.clear();
            }
            if (mCallbacks != null && mCallbacks.get() != null) {
                stopLoaderLocked();
                mLoaderTask = new LoaderTask(mApp.getContext(), loadFlags);//3
                if (synchronousBindPage != PagedView.INVALID_RESTORE_PAGE
                        && mAllAppsLoaded && mWorkspaceLoaded && !mIsLoaderTaskRunning) {
                    mLoaderTask.runBindSynchronousPage(synchronousBindPage);
                } else {
                    sWorkerThread.setPriority(Thread.NORM_PRIORITY);
                    sWorker.post(mLoaderTask);//4
                }
            }
        }
    }

注釋1處創(chuàng)建了具有消息循環(huán)的線程HandlerThread對(duì)象羊瘩。注釋2處創(chuàng)建了Handler泰佳，并且傳入HandlerThread的Looper。Hander的作用就是向HandlerThread發(fā)送消息尘吗。在注釋3處創(chuàng)建LoaderTask逝她，在注釋4處將LoaderTask作為消息發(fā)送給HandlerThread 。 LoaderTask類實(shí)現(xiàn)了Runnable接口睬捶，當(dāng)LoaderTask所描述的消息被處理時(shí)則會(huì)調(diào)用它的run函數(shù)

private class LoaderTask implements Runnable {
 ...
        public void run() {
            synchronized (mLock) {
                if (mStopped) {
                    return;
                }
                mIsLoaderTaskRunning = true;
            }
            keep_running: {
                if (DEBUG_LOADERS) Log.d(TAG, "step 1: loading workspace");
                loadAndBindWorkspace();//1
                if (mStopped) {
                    break keep_running;
                }
                waitForIdle();
                if (DEBUG_LOADERS) Log.d(TAG, "step 2: loading all apps");
                loadAndBindAllApps();//2
            }
            mContext = null;
            synchronized (mLock) {
                if (mLoaderTask == this) {
                    mLoaderTask = null;
                }
                mIsLoaderTaskRunning = false;
                mHasLoaderCompletedOnce = true;
            }
        }
   ...     
  }      

Launcher是用工作區(qū)的形式來(lái)顯示系統(tǒng)安裝的應(yīng)用程序的快捷圖標(biāo)黔宛，每一個(gè)工作區(qū)都是來(lái)描述一個(gè)抽象桌面的，它由n個(gè)屏幕組成擒贸，每個(gè)屏幕又分n個(gè)單元格臀晃，每個(gè)單元格用來(lái)顯示一個(gè)應(yīng)用程序的快捷圖標(biāo)。注釋1處調(diào)用loadAndBindWorkspace函數(shù)用來(lái)加載工作區(qū)信息介劫，注釋2處的loadAndBindAllApps函數(shù)是用來(lái)加載系統(tǒng)已經(jīng)安裝的應(yīng)用程序信息

private void loadAndBindAllApps() {
    if (DEBUG_LOADERS) {
        Log.d(TAG, "loadAndBindAllApps mAllAppsLoaded=" + mAllAppsLoaded);
    }
    if (!mAllAppsLoaded) {
        loadAllApps();//1
        synchronized (LoaderTask.this) {
            if (mStopped) {
                return;
            }
        }
        updateIconCache();
        synchronized (LoaderTask.this) {
            if (mStopped) {
                return;
            }
            mAllAppsLoaded = true;
        }
    } else {
        onlyBindAllApps();
    }
}

如果系統(tǒng)沒(méi)有加載已經(jīng)安裝的應(yīng)用程序信息徽惋，則會(huì)調(diào)用注釋1處的loadAllApps函數(shù)：

 private void loadAllApps() {
...
        mHandler.post(new Runnable() {
            public void run() {
                final long bindTime = SystemClock.uptimeMillis();
                final Callbacks callbacks = tryGetCallbacks(oldCallbacks);
                if (callbacks != null) {
                    callbacks.bindAllApplications(added);//1
                    if (DEBUG_LOADERS) {
                        Log.d(TAG, "bound " + added.size() + " apps in "
                                + (SystemClock.uptimeMillis() - bindTime) + "ms");
                    }
                } else {
                    Log.i(TAG, "not binding apps: no Launcher activity");
                }
            }
        });
       ...
    }

在注釋1處會(huì)調(diào)用callbacks的bindAllApplications函數(shù)，在前面我們得知這個(gè)callbacks實(shí)際是指向Launcher的座韵，因此我們來(lái)查看Launcher的bindAllApplications函數(shù) packages/apps/Launcher3/src/com/android/launcher3/Launcher.java

public void bindAllApplications(final ArrayList<AppInfo> apps) {
    if (waitUntilResume(mBindAllApplicationsRunnable, true)) {
        mTmpAppsList = apps;
        return;
    }
    if (mAppsView != null) {
        mAppsView.setApps(apps);//1
    }
    if (mLauncherCallbacks != null) {
        mLauncherCallbacks.bindAllApplications(apps);
    }
}

注釋1處會(huì)調(diào)用AllAppsContainerView的setApps函數(shù)险绘，并將包含應(yīng)用信息的列表apps傳進(jìn)去 packages/apps/Launcher3/src/com/android/launcher3/allapps/AllAppsContainerView.java

  public void setApps(List<AppInfo> apps) {
        mApps.setApps(apps);
    }

包含應(yīng)用信息的列表apps已經(jīng)設(shè)置到了AllAppsContainerView的AlphabeticalAppsList中，查看AllAppsContainerView的onFinishInflate函數(shù)：

@Override
    protected void onFinishInflate() {
        super.onFinishInflate();
...
        // Load the all apps recycler view
        mAppsRecyclerView = (AllAppsRecyclerView) findViewById(R.id.apps_list_view);//1
        mAppsRecyclerView.setApps(mApps);//2
        mAppsRecyclerView.setLayoutManager(mLayoutManager);
        mAppsRecyclerView.setAdapter(mAdapter);//3
        mAppsRecyclerView.setHasFixedSize(true);
        mAppsRecyclerView.addOnScrollListener(mElevationController);
        mAppsRecyclerView.setElevationController(mElevationController);
...
    }

onFinishInflate函數(shù)在加載完xml文件時(shí)就會(huì)調(diào)用，在注釋1處得到AllAppsRecyclerView用來(lái)顯示App列表隆圆，并在注釋2處將apps的信息列表傳進(jìn)去漱挚，并在注釋3處為AllAppsRecyclerView設(shè)置Adapter。這樣應(yīng)用程序快捷圖標(biāo)的列表就會(huì)顯示在屏幕上渺氧。

總結(jié) Launcher的啟動(dòng)流程

Zygote進(jìn)程 –> SystemServer進(jìn)程 –> startOtherService方法 –> ActivityManagerService的systemReady方法 –> startHomeActivityLocked方法 –> ActivityStackSupervisor的startHomeActivity方法 –> 執(zhí)行Activity的啟動(dòng)邏輯旨涝，執(zhí)行scheduleResumeTopActivities()方法

因?yàn)槭请[試的啟動(dòng)Activity，所以啟動(dòng)的Activity就是在AndroidManifest.xml中配置catogery的值為：

public static final String CATEGORY_HOME = "android.intent.category.HOME";