省略一萬字前奏
如果大家沒有源碼，
不介意的話，可以參考https://github.com/Tic-pf/Launcher3-N-Folder 開發中

主入口Launcher

LauncherAppState

Launcher的onCreate里比較長，我們依次取代碼片段來分析，看oncrate方法的這一段,初始化LauncherAppState

public void onCreate() {
    ...
    LauncherAppState app = LauncherAppState.getInstance();
    ...
}
    

LauncherAppState是保存一些全局的，核心的對象。主要有整個Launcher的工作臺workspace，Launcher的控制器LauncherModel，應用圖標的緩存機制IconCache，設備的配置信息InvariantDeviceProfile等。

構造方法，首先初始化內存的追蹤器TestingUtils，記錄我們app的內存信息，這個工具在我們開發其他app分析內存信息時也是很有用的。

private LauncherAppState() {
    ...

    if (TestingUtils.MEMORY_DUMP_ENABLED) {
        TestingUtils.startTrackingMemory(sContext);
    }

    mInvariantDeviceProfile = new InvariantDeviceProfile(sContext);
    mIconCache = new IconCache(sContext, mInvariantDeviceProfile);
    mWidgetCache = new WidgetPreviewLoader(sContext, mIconCache);

    mAppFilter = AppFilter.loadByName(sContext.getString(R.string.app_filter_class));
    mModel = new LauncherModel(this, mIconCache, mAppFilter);

    LauncherAppsCompat.getInstance(sContext).addOnAppsChangedCallback(mModel);

    // Register intent receivers
    IntentFilter filter = new IntentFilter();
    filter.addAction(Intent.ACTION_LOCALE_CHANGED);
    filter.addAction(SearchManager.INTENT_GLOBAL_SEARCH_ACTIVITY_CHANGED);
    // For handling managed profiles
    filter.addAction(LauncherAppsCompat.ACTION_MANAGED_PROFILE_ADDED);
    filter.addAction(LauncherAppsCompat.ACTION_MANAGED_PROFILE_REMOVED);
    filter.addAction(LauncherAppsCompat.ACTION_MANAGED_PROFILE_AVAILABLE);
    filter.addAction(LauncherAppsCompat.ACTION_MANAGED_PROFILE_UNAVAILABLE);

    sContext.registerReceiver(mModel, filter);
    ...
}         

LauncherAppsCompat里添加了一個應用變化的回調，由LauncherModel實現接口，及時的響應數據變化。LauncherAppsCompat是獲取所有應用，監聽應用變化的一個抽象，Android 5.0前后的版本獲取方式不一樣了，這就是Launcher良好適配性的體現了。

        LauncherAppsCompat.getInstance(sContext).addOnAppsChangedCallback(mModel);

Android 5.0以前的監聽

private void registerForPackageIntents() {
    IntentFilter filter = new IntentFilter(Intent.ACTION_PACKAGE_ADDED);
    filter.addAction(Intent.ACTION_PACKAGE_REMOVED);
    filter.addAction(Intent.ACTION_PACKAGE_CHANGED);
    filter.addDataScheme("package");
    mContext.registerReceiver(mPackageMonitor, filter);
    filter = new IntentFilter();
    filter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE);
    filter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE);
    mContext.registerReceiver(mPackageMonitor, filter);
}

Android5.0后的監聽

import android.content.pm.LauncherApps;

protected LauncherApps mLauncherApps;

public void addOnAppsChangedCallback(LauncherAppsCompat.OnAppsChangedCallbackCompat callback) {
    WrappedCallback wrappedCallback = new WrappedCallback(callback);
    synchronized (mCallbacks) {
        mCallbacks.put(callback, wrappedCallback);
    }
    mLauncherApps.registerCallback(wrappedCallback);
}

除了TestingUtils，應用變化監聽外，初始化兩個核心對象IconCache，LauncherModel。LauncherModel添加了設備變更，用戶信息變更的廣播，這是因為當用戶修改設備信息如語言，區域，用戶信息等，LauncherModel會刷新數據，改變圖標，標題等信息。
LauncherAppState的初始化到這里基本上就完成了。

DeviceProfile，InvariantDeviceProfile，Launcher的配置

我們繼續看，下一步

LauncherAppState app = LauncherAppState.getInstance();

// Load configuration-specific DeviceProfile
mDeviceProfile = getResources().getConfiguration().orientation
        == Configuration.ORIENTATION_LANDSCAPE ?
        app.getInvariantDeviceProfile().landscapeProfile
        : app.getInvariantDeviceProfile().portraitProfile;

通過Configuration獲取橫屏配置landscapeProfile 或者portraitProfile豎屏配置

DeviceProfile

DeviceProfile的數據都是來自InvariantDeviceProfile，封裝一些工具方法，我們直接看重點InvariantDeviceProfile

InvariantDeviceProfile

InvariantDeviceProfile的初始化是在LauncherAppState構造里new出來的，調用的是

InvariantDeviceProfile(Context context) {
    ...
    numRows = closestProfile.numRows;
    numColumns = closestProfile.numColumns;
    numHotseatIcons = closestProfile.numHotseatIcons;
    hotseatAllAppsRank = (int) (numHotseatIcons / 2);
    defaultLayoutId = closestProfile.defaultLayoutId;
    numFolderRows = closestProfile.numFolderRows;
    numFolderColumns = closestProfile.numFolderColumns;
    minAllAppsPredictionColumns = closestProfile.minAllAppsPredictionColumns;

    iconSize = interpolatedDeviceProfileOut.iconSize;
    iconBitmapSize = Utilities.pxFromDp(iconSize, dm);
    iconTextSize = interpolatedDeviceProfileOut.iconTextSize;
    hotseatIconSize = interpolatedDeviceProfileOut.hotseatIconSize;
    fillResIconDpi = getLauncherIconDensity(iconBitmapSize);

    // If the partner customization apk contains any grid overrides, apply them
    // Supported overrides: numRows, numColumns, iconSize
    applyPartnerDeviceProfileOverrides(context, dm);

    Point realSize = new Point();
    display.getRealSize(realSize);
    // The real size never changes. smallSide and largeSide will remain the
    // same in any orientation.
    int smallSide = Math.min(realSize.x, realSize.y);
    int largeSide = Math.max(realSize.x, realSize.y);

    landscapeProfile = new DeviceProfile(context, this, smallestSize, largestSize,
            largeSide, smallSide, true /* isLandscape */);
    portraitProfile = new DeviceProfile(context, this, smallestSize, largestSize,
            smallSide, largeSide, false /* isLandscape */);
}

可以看到，通過closestProfile和interpolatedDeviceProfileOut拿到了一系列配置項，如桌面的行，列，Hotseat(桌面底部固定的應用欄)的個數，Hotseat所有應用的位置，布局id，文件夾的行列，圖標的大小等等。之后再將這些信息new出我們的DeviceProfile對象。
那問題來了，closestProfile和interpolatedDeviceProfileOut是什么？？怎么計算出來的？

...
WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
Display display = wm.getDefaultDisplay();
DisplayMetrics dm = new DisplayMetrics();
display.getMetrics(dm);

Point smallestSize = new Point();
Point largestSize = new Point();
display.getCurrentSizeRange(smallestSize, largestSize);

// This guarantees that width < height
minWidthDps = Utilities.dpiFromPx(Math.min(smallestSize.x, smallestSize.y), dm);
minHeightDps = Utilities.dpiFromPx(Math.min(largestSize.x, largestSize.y), dm);

ArrayList<InvariantDeviceProfile> closestProfiles =
        findClosestDeviceProfiles(minWidthDps, minHeightDps, getPredefinedDeviceProfiles());
InvariantDeviceProfile interpolatedDeviceProfileOut =
        invDistWeightedInterpolate(minWidthDps,  minHeightDps, closestProfiles);
...

可以發現，通過設備的寬高等信息，從各種分辨率的DeviceProfiles列表中找到最合適的配置信息，查找的方法如下，根據設備的寬高跟列表里的的最小寬高差值的平方根從小到大排序，第一個就是我們期望的配置

/**
 * Returns the closest device profiles ordered by closeness to the specified width and height
 */
// Package private visibility for testing.
ArrayList<InvariantDeviceProfile> findClosestDeviceProfiles(
        final float width, final float height, ArrayList<InvariantDeviceProfile> points) {

    // Sort the profiles by their closeness to the dimensions
    ArrayList<InvariantDeviceProfile> pointsByNearness = points;
    Collections.sort(pointsByNearness, new Comparator<InvariantDeviceProfile>() {
        public int compare(InvariantDeviceProfile a, InvariantDeviceProfile b) {
            return Float.compare(dist(width, height, a.minWidthDps, a.minHeightDps),
                    dist(width, height, b.minWidthDps, b.minHeightDps));
        }
    });

    return pointsByNearness;
}

@Thunk float dist(float x0, float y0, float x1, float y1) {
    return (float) Math.hypot(x1 - x0, y1 - y0);
}

配置好的InvariantDeviceProfile列表信息如下，構造參數依次是，
配置名稱，寬高，行數，列數，文件夾行數列數，圖標大小，圖標文本大小
hotseat配置資源文件，hotseat圖標大小，默認頁的資源文件
故，當我們有新機型沒有適配，就可以在這里修改或新增配置

ArrayList<InvariantDeviceProfile> getPredefinedDeviceProfiles() {
    ArrayList<InvariantDeviceProfile> predefinedDeviceProfiles = new ArrayList<>();
    // width, height, #rows, #columns, #folder rows, #folder columns,
    // iconSize, iconTextSize, #hotseat, #hotseatIconSize, defaultLayoutId.
    predefinedDeviceProfiles.add(new InvariantDeviceProfile("Super Short Stubby",
            255, 300,     2, 3, 2, 3, 3, 48, 13, 3, 48, R.xml.default_workspace_3x3));
    predefinedDeviceProfiles.add(new InvariantDeviceProfile("Shorter Stubby",
            255, 400,     3, 3, 3, 3, 3, 48, 13, 3, 48, R.xml.default_workspace_3x3));
    predefinedDeviceProfiles.add(new InvariantDeviceProfile("Short Stubby",
            275, 420,     3, 4, 3, 4, 4, 48, 13, 5, 48, R.xml.default_workspace_4x4));
    predefinedDeviceProfiles.add(new InvariantDeviceProfile("Stubby",
            255, 450,     3, 4, 3, 4, 4, 48, 13, 5, 48, R.xml.default_workspace_4x4));
    predefinedDeviceProfiles.add(new InvariantDeviceProfile("Nexus S",
            296, 491.33f, 4, 4, 4, 4, 4, 48, 13, 5, 48, R.xml.default_workspace_4x4));
    predefinedDeviceProfiles.add(new InvariantDeviceProfile("Nexus 4",
            359, 567,     4, 4, 4, 4, 4, DEFAULT_ICON_SIZE_DP, 13, 5, 56, R.xml.default_workspace_4x4));
    predefinedDeviceProfiles.add(new InvariantDeviceProfile("Nexus 5",
            335, 567,     5, 4, 5, 4, 4, DEFAULT_ICON_SIZE_DP, 13, 5, 56, R.xml.default_workspace_5x4_no_all_apps));
    predefinedDeviceProfiles.add(new InvariantDeviceProfile("Large Phone",
            406, 694,     5, 5, 4, 4, 4, 64, 14.4f,  5, 56, R.xml.default_workspace_5x5));
    // The tablet profile is odd in that the landscape orientation
    // also includes the nav bar on the side
    predefinedDeviceProfiles.add(new InvariantDeviceProfile("Nexus 7",
            575, 904,     5, 6, 4, 5, 4, 72, 14.4f,  7, 60, R.xml.default_workspace_5x6));
    // Larger tablet profiles always have system bars on the top & bottom
    predefinedDeviceProfiles.add(new InvariantDeviceProfile("Nexus 10",
            727, 1207,    5, 6, 4, 5, 4, 76, 14.4f,  7, 76, R.xml.default_workspace_5x6));
    predefinedDeviceProfiles.add(new InvariantDeviceProfile("20-inch Tablet",
            1527, 2527,   7, 7, 6, 6, 4, 100, 20,  7, 72, R.xml.default_workspace_5x6));
    return predefinedDeviceProfiles;
}

Launcher的配置初始化到這里基本上就完成了。

還有一些其他的對象的初始化，包括workspace狀態變化的動畫加載控制LauncherStateTransitionAnimation, 應用組件的管理器AppWidgetManagerCompat, 處理組件長按事件的ViewLauncherAppWidgetHost，因為在Launcher的初始化流程里不是特別需要，故后文有機會再做介紹。

LauncherModel加載應用信息

整個流程里比較復雜的就是LauncherModel加載應用了, 在onCreate里

    mModel = app.setLauncher(this);
    

LauncherAppState里調用了LauncherModel的初始化方法 initialize,參數是Launcher

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

LauncherModel的initialize參數是LauncherModel.Callbacks，Launcher里實現了LauncherModel.Callbacks的一系列接口用于綁定獲取到的應用信息，文件夾信息，屏幕信息等等

 public void initialize(Callbacks callbacks) {
        synchronized (mLock) {
            // Disconnect any of the callbacks and drawables associated with ItemInfos on the
            // workspace to prevent leaking Launcher activities on orientation change.
            unbindItemInfosAndClearQueuedBindRunnables();
            mCallbacks = new WeakReference<Callbacks>(callbacks);
        }
    }

在加載數據之前先清除正在運行的線程DeferredBindRunnables，清除DeferredHandler里等待執行的任務，并且將所有ItemInfo unbind

/** Unbinds all the sBgWorkspaceItems and sBgAppWidgets on the main thread */
void unbindWorkspaceItemsOnMainThread() {
    // Ensure that we don't use the same workspace items data structure on the main thread
    // by making a copy of workspace items first.
    final ArrayList<ItemInfo> tmpItems = new ArrayList<ItemInfo>();
    synchronized (sBgLock) {
        tmpItems.addAll(sBgWorkspaceItems);
        tmpItems.addAll(sBgAppWidgets);
    }
    Runnable r = new Runnable() {
            @Override
            public void run() {
                for (ItemInfo item : tmpItems) {
                    item.unbind();
                }
            }
        };
    runOnMainThread(r);
}

接著我們才看到真正開始加載數據了，onCreate里的LauncherModel調用startLoader，創建線程加載數據

        ...        
        if (!mRestoring) {
            if (DISABLE_SYNCHRONOUS_BINDING_CURRENT_PAGE) {
                // If the user leaves launcher, then we should just load items asynchronously when
                // they return.
                mModel.startLoader(PagedView.INVALID_RESTORE_PAGE);
            } else {
                // We only load the page synchronously if the user rotates (or triggers a
                // configuration change) while launcher is in the foreground
                mModel.startLoader(mWorkspace.getRestorePage());
            }
        }
        ...
        

當第一次打開時，會調用 mModel.startLoader(PagedView.INVALID_RESTORE_PAGE)，停止舊的Loader任務，stopLoaderLocked，然后new出一個LoaderTask(mApp.getContext(), loadFlags) Runnable，通過Handler sworker post出去，開始加載任務

public void startLoader(int synchronousBindPage) {
    startLoader(synchronousBindPage, LOADER_FLAG_NONE);
}

public void startLoader(int synchronousBindPage, int loadFlags) {
        // Enable queue before starting loader. It will get disabled in Launcher#finishBindingItems
        InstallShortcutReceiver.enableInstallQueue();
        synchronized (mLock) {
            // Clear any deferred bind-runnables from the synchronized load process
            // We must do this before any loading/binding is scheduled below.
            synchronized (mDeferredBindRunnables) {
                mDeferredBindRunnables.clear();
            }

            // Don't bother to start the thread if we know it's not going to do anything
            if (mCallbacks != null && mCallbacks.get() != null) {
                // If there is already one running, tell it to stop.
                stopLoaderLocked();
                mLoaderTask = new LoaderTask(mApp.getContext(), loadFlags);
                if (synchronousBindPage != PagedView.INVALID_RESTORE_PAGE
                        && mAllAppsLoaded && mWorkspaceLoaded && !mIsLoaderTaskRunning) {
                    mLoaderTask.runBindSynchronousPage(synchronousBindPage);
                } else {
                    sWorkerThread.setPriority(Thread.NORM_PRIORITY);
                    sWorker.post(mLoaderTask);
                }
            }
        }
    }

開始加載應用信息的任務后，由于后續的篇幅比較長，請看下一篇文章的詳細介紹。