告别单调：Android用户必学的系统主题切换攻略

项目需求：编写主题app，一键切换桌面app图标和系统壁纸。
Android版本：8.1

需求是写一个系统主题app，实现类似于华为手机内置系统主题app的功能，原生android是没有主题app的，网上都是app换肤框架，是给自己单独的app换主题，百般无奈只能自己动手写了。还好我们是在源码基础上开发，可以任性的自定义功能。

步骤一

先找到Launcher加载各种app的地方

Launcher的初始化过程:

@OverrideprotectedvoidonCreate(Bundle savedInstanceState){...
		LauncherAppState app = LauncherAppState.getInstance(this);
		mModel = app.setLauncher(this);...if(!mModel.startLoader(currentScreen)){
            mDragLayer.setAlpha(0);}else{
            mWorkspace.setCurrentPage(currentScreen);setWorkspaceLoading(true);}...}

进入LauncherModel，发现LauncherModel 居然是BroadcastReceiver

publicclassLauncherModelextendsBroadcastReceiver

去看它的startLoader

publicbooleanstartLoader(int synchronousBindPage){// Enable queue before starting loader. It will get disabled in Launcher#finishBindingItems
        InstallShortcutReceiver.enableInstallQueue(InstallShortcutReceiver.FLAG_LOADER_RUNNING);synchronized(mLock){if(mCallbacks != null && mCallbacks.get()!= null){final Callbacks oldCallbacks = mCallbacks.get();// Clear any pending bind-runnables from the synchronized load process.
                mUiExecutor.execute(newRunnable(){publicvoidrun(){
                                oldCallbacks.clearPendingBinds();}});stopLoader();
                LoaderResults loaderResults =newLoaderResults(mApp, sBgDataModel,
                        mBgAllAppsList, synchronousBindPage, mCallbacks);if(mModelLoaded &&!mIsLoaderTaskRunning){
                    loaderResults.bindWorkspace();
                    loaderResults.bindAllApps();
                    loaderResults.bindDeepShortcuts();
                    loaderResults.bindWidgets();returntrue;}else{startLoaderForResults(loaderResults);}}}returnfalse;}

第一次初始化mModelLoaded肯定是false无疑，所以进入startLoaderForResults(loaderResults)

publicvoidstartLoaderForResults(LoaderResults results){synchronized(mLock){stopLoader();
            mLoaderTask =newLoaderTask(mApp, mBgAllAppsList, sBgDataModel, results,packName,themeName);runOnWorkerThread(mLoaderTask);}}

LoaderTask是一个Runnable,

privatestaticvoidrunOnWorkerThread(Runnable r){if(sWorkerThread.getThreadId()== Process.myTid()){
            r.run();}else{// If we are not on the worker thread, then post to the worker handler
            sWorker.post(r);}}

所以应该去看LoaderTask的run方法

publicvoidrun(){synchronized(this){// Skip fast if we are already stopped.if(mStopped){return;}}try(LauncherModel.LoaderTransaction transaction = mApp.getModel().beginLoader(this)){if(DEBUG_LOADERS) Log.d(TAG,"step 1.1: loading workspace");loadWorkspace();if(DEBUG_LOADERS) Log.d(TAG,"step 1.2: bind workspace workspace");
            mResults.bindWorkspace();if(DEBUG_LOADERS) Log.d(TAG,"step 2.1: loading all apps");loadAllApps();
            mResults.bindAllApps();if(DEBUG_LOADERS) Log.d(TAG,"step 2.3: Update icon cache");updateIconCache();// third stepif(DEBUG_LOADERS) Log.d(TAG,"step 3.1: loading deep shortcuts");loadDeepShortcuts();if(DEBUG_LOADERS) Log.d(TAG,"step 3.2: bind deep shortcuts");
            mResults.bindDeepShortcuts();// fourth stepif(DEBUG_LOADERS) Log.d(TAG,"step 4.1: loading widgets");
            mBgDataModel.widgetsModel.update(mApp, null);if(DEBUG_LOADERS) Log.d(TAG,"step 4.2: Binding widgets");
            mResults.bindWidgets();
            transaction.commit();}catch(CancellationException e){}}

这个方法很大，但是逻辑是顺序的，分别先加载并绑定了 workspace ，然后再加载所有app的view，由于我们想找到的是加载app图标的地方，所以肯定是 loadAllApps 了。

privatevoidloadAllApps(){finallong loadTime = DEBUG_LOADERS ? SystemClock.uptimeMillis():0;final List<UserHandle> profiles = mUserManager.getUserProfiles();
        mBgAllAppsList.clear();for(UserHandle user : profiles){...//省略// Create the ApplicationInfosfor(int i =0; i < apps.size(); i++){
                LauncherActivityInfo app = apps.get(i);// This builds the icon bitmaps.
                Log.i(TAG,"loadAllApps--> app="+ app.getName());
                mBgAllAppsList.add(newAppInfo(app, user, quietMode), app);}...//省略
            ManagedProfileHeuristic.onAllAppsLoaded(mApp.getContext(), apps, user);}...//省略}

其中，for循环用LauncherActivityInfo封装给AppInfo，再添加进list里，

publicvoidadd(AppInfo info, LauncherActivityInfo activityInfo){if(!mAppFilter.shouldShowApp(info.componentName)){return;}if(findAppInfo(info.componentName, info.user)!= null){return;}
        mIconCache.getTitleAndIcon(info, activityInfo,true/* useLowResIcon */);
        data.add(info);
        added.add(info);}

进入了AllAppsList，使用的是IconCache来管理appinfo的，

publicsynchronizedvoidgetTitleAndIcon(ItemInfoWithIcon info,
            LauncherActivityInfo activityInfo,boolean useLowResIcon){// If we already have activity info, no need to use package icongetTitleAndIcon(info, Provider.of(activityInfo),false, useLowResIcon);}---privatesynchronizedvoidgetTitleAndIcon(@NonNull ItemInfoWithIcon infoInOut,@NonNull Provider<LauncherActivityInfo> activityInfoProvider,boolean usePkgIcon,boolean useLowResIcon){
        CacheEntry entry =cacheLocked(infoInOut.getTargetComponent(), activityInfoProvider,
                infoInOut.user, usePkgIcon, useLowResIcon);applyCacheEntry(entry, infoInOut);}

继续封装AppInfo

protected CacheEntry cacheLocked(@NonNull ComponentName componentName,@NonNull Provider<LauncherActivityInfo> infoProvider,
            UserHandle user,boolean usePackageIcon,boolean useLowResIcon){
        Preconditions.assertWorkerThread();
        ComponentKey cacheKey =newComponentKey(componentName, user);
        CacheEntry entry = mCache.get(cacheKey);if(entry == null ||(entry.isLowResIcon &&!useLowResIcon)){
            entry =newCacheEntry();
            mCache.put(cacheKey, entry);// Check the DB first.
            LauncherActivityInfo info = null;boolean providerFetchedOnce =false;if(!getEntryFromDB(cacheKey, entry, useLowResIcon)|| DEBUG_IGNORE_CACHE){
                info = infoProvider.get();
                providerFetchedOnce =true;if(info != null){
                    Log.i(TAG,"cacheLocked--> 1 create icon ="+info.getName());
                    entry.icon = LauncherIcons.createBadgedIconBitmap(getFullResIcon(info), info.getUser(), mContext,
                            infoProvider.get().getApplicationInfo().targetSdkVersion);}}...//省略}return entry;}

在LauncherIcons的createBadgedIconBitmap里处理appIcon，其中第一个参数来自于getFullResIcon(info)

public Drawable getFullResIcon(LauncherActivityInfo info){returngetFullResIcon(info,true);}---public Drawable getFullResIcon(LauncherActivityInfo info,boolean flattenDrawable){return mIconProvider.getIcon(info, mIconDpi, flattenDrawable);}---public Drawable getIcon(LauncherActivityInfo info,int iconDpi,boolean flattenDrawable){return info.getIcon(iconDpi);}

获取的Icon资源来自于 LauncherActivityInfo

public Drawable getIcon(int density){// TODO: Go through LauncherAppsServicefinalint iconRes = mActivityInfo.getIconResource();
        Drawable icon = null;// Get the preferred density icon from the app's resourcesif(density !=0&& iconRes !=0){try{final Resources resources
                        = mPm.getResourcesForApplication(mActivityInfo.applicationInfo);
                icon = resources.getDrawableForDensity(iconRes, density);}catch(NameNotFoundException| Resources.NotFoundException exc){}}// Get the default density iconif(icon == null){
            icon = mActivityInfo.loadIcon(mPm);}return icon;}

关键点就是

final Resources resources
            = mPm.getResourcesForApplication(mActivityInfo.applicationInfo);
    icon = resources.getDrawableForDensity(iconRes, density);

通过各个app的启动Activity（就是每个app都有的主Activity），获取到对应的ApplicationInfo，然后获取到对应包的资源Resources，然后根据那个Resources找到对应Id的drawable.

所以我们找到了Launcher加载app列表，获取app图标的地方了，接下来就是怎么拦截这个操作，使用我们自己主题app的图标了。

步骤二

使Launcher加载我们自己写的包里的资源。

在上面的获取Resources的时候，是通过对应的ApplicationInfo来获取的，也就是每个应用程序都有自己对应的Resources对象来管理当前app的资源，我们怎么去获取到我们自己写的包的Resources呢，如果要先去获取Activityinfo，那就很绕弯了，很巧的是，还有个可用的重载方法。

getResourcesForApplication(ApplicationInfo app)getResourcesForApplication(String appPackageName)

直接根据包名就可以获取到资源Resources对象，当然这里的报名直接写我们自己的app包名。

所以接下来就是在getFullResIcon那里做拦截，先到我们写的app里找资源，更改如下

public Drawable getFullResIcon(LauncherActivityInfo info,boolean flattenDrawable){if(!TextUtils.isEmpty(mPackname)){
            Drawable drawable =getFullResIconLanco(info.getActivityInfo());if(drawable != null){return drawable;}}return mIconProvider.getIcon(info, mIconDpi, flattenDrawable);}

public Drawable getFullResIconLanco(ActivityInfo info){
        Drawable drawable = null;
        Resources resourcesX;
        Resources resourcesY;try{
            resourcesX= mPackageManager.getResourcesForApplication(
                    info.applicationInfo);
            resourcesY = mPackageManager.getResourcesForApplication(
                    mPackname);}catch(PackageManager.NameNotFoundException e){
            resourcesX = null;
            resourcesY = null;}if(resourcesX != null && resourcesY != null){int iconId = info.getIconResource();if(iconId !=0){
                drawable =getFullResIcon(resourcesX, resourcesY, iconId);if(drawable != null){return drawable;}}}return drawable;}

当获取对应Icon的时候，一并得到我们自己app的Resources

private Drawable getFullResIcon(Resources resourcesReal,Resources resourcesFake,int iconId){
        Drawable d;try{
            String name = resourcesReal.getResourceEntryName(iconId);
            String type = resourcesReal.getResourceTypeName(iconId);if(!mThemename.equals("")){
                name = name +"_"+ mThemename;}int fakeid = resourcesFake.getIdentifier(name,"drawable", mPackname);
            Log.i(TAG,"getFullResIcon--> name = "+ name +"--type ="+ type+"--iconId="+iconId+"--fakeid="+fakeid);
            d = resourcesFake.getDrawableForDensity(fakeid, mIconDpi);}catch(Resources.NotFoundException e){
            d = null;}return d ;}

根据真实的Resources获取到对应icon的名称，然后根据名称，在我们写的app的Resources里找到同名的id，再找到对应的Drawable。
其中，根据mThemename主题名称的不同，我们加载不同的icon名称，
比如：如果主题名字叫theme，正常的appIcon名称 ic_launcher_main， 对应我们包里的icon就命名成ic_launcher_main_theme， 不同主题加不同的后缀，用于区分不同的id，
关于mThemename和mPackname，主题名和包名的传递，是在我们自己app里直接发送Intent过来的，然后把对应名称设置到IconCache这个类里来就行了，别忘了，前面特别提到LauncherModel是个BroadcastReceiver，发广播的事情不提了。

步骤三

在我们的app里定义不同的主题包

首先要内置第三方app，然后在makefile里区别资源包，我的方法是给出三个目录

LOCAL_RESOURCE_DIR := \
    $(LOCAL_PATH)/res \
    $(LOCAL_PATH)/res_fake\
    $(LOCAL_PATH)/res_xposed \

创建不同的主题资源，其余的就是对应图片命名，然后别忘了引用他们，不然编译不能生成对应R资源。

<resources><drawable name="ic_launcher_browser_fake">@drawable/ic_launcher_browser_fake</drawable><drawable name="ic_launcher_phone_fake">@drawable/ic_launcher_phone_fake</drawable><drawable name="ic_launcher_mms_fake">@drawable/ic_launcher_mms_fake</drawable></resources>

然后R文件里就会有我们的ID了，

publicstaticfinalint ic_launcher_browser_fake=0x7f08006e;publicstaticfinalint ic_launcher_phone_fake=0x7f080080;publicstaticfinalint ic_launcher_mms_fake=0x7f08007d;

这样，在Launcher找我们包里的图片的时候，找的就是这些我们加进来的图片id.

Tips

Launcher 初始化之后，就不会再加载一次图片，因为那些app列表信息会存储到数据库里，要想每次我们切换主题都有效，就必须强制清空数据，

mIconCache.clear();

这是必须的，以及

if(clearDb){
        Log.d(TAG,"loadWorkspace: resetting launcher database");
        LauncherSettings.Settings.call(contentResolver,
                LauncherSettings.Settings.METHOD_CREATE_EMPTY_DB);}

这是清除数据库，具体的都在源码里。只有这样才会更新，不然就从缓存里和数据库里找资源了。

步骤四

更改对应壁纸

这里只需要在切换主题的时候更换壁纸，

try{if(mWallPaperid ==0){clearWallpaper();}else{
            WallpaperManager.getInstance(this).setBitmap(BitmapFactory.decodeResource(getResources(), mWallPaperid));}}catch(IOException e){
        e.printStackTrace();}

效果图：