Arouter原理分析-白红宇

在app的开发中，页面之间的相互跳转是最基本常用的功能。在Android中的跳转一般通过显式intent和隐式intent两种方式实现的，而Android的原生跳转方式会存在一些缺点：

显式intent的实现方式，因为会存在直接的类依赖的问题，导致耦合严重；隐式intent的实现方式，则会出现规则集中式管理，导致协作变得困难；可配置性较差，一般而言配置规则都是在Manifest中的，这就导致了扩展性较差；跳转过程无法控制，一旦使用了StartActivity()就无法插手其中任何环节了，只能交给系统管理；特别是当使用多组件化开发时，使用原生的路由方式很难实现完全解耦；

而阿里的ARouter路由框架具有解耦、简单易用、支持多模块项目、定制性较强、支持拦截逻辑等诸多优点，很好的解决了上述的问题。

Arouter原理

ARouter在编译时会生成module下生成这些文件

public class ARouter$$Root$$app implements IRouteRoot {   @Override   public void loadInto(Map
      
       > routes) {     routes.put("app", ARouter$$Group$$app.class);   } } public class ARouter$$Group$$app implements IRouteGroup {   @Override   public void loadInto(Map
       
         atlas) {     atlas.put("/app/main", RouteMeta.build(RouteType.ACTIVITY, MainActivity.class, "/app/main", "app", null, -1, -2147483648));     atlas.put("/app/second", RouteMeta.build(RouteType.ACTIVITY, SecondActivity.class, "/app/second", "app", null, -1, -2147483648));   } } public class ARouter$$Providers$$app implements IProviderGroup {   @Override   public void loadInto(Map
        
          providers) {   } }复制代码

接着看一下初始化方法

public static void init(Application application) {     if (!hasInit) {         logger = _ARouter.logger;         _ARouter.logger.info(Consts.TAG, "ARouter init start.");         hasInit = _ARouter.init(application);         if (hasInit) {             _ARouter.afterInit();         }         _ARouter.logger.info(Consts.TAG, "ARouter init over.");     } }复制代码

调用了_ARouter.init方法后接着就调用 _ARouter.afterInit方法

跟进_ARouter.init方法

protected static synchronized boolean init(Application application) {     mContext = application;     LogisticsCenter.init(mContext, executor);     logger.info(Consts.TAG, "ARouter init success!");     hasInit = true;     mHandler = new Handler(Looper.getMainLooper());     return true; }复制代码

最主要的是ogisticsCenter.init(mContext, executor)这一句，其他的都是进行基本的赋值

public synchronized static void init(Context context, ThreadPoolExecutor tpe) throws HandlerException {     mContext = context;     executor = tpe;     try {         long startInit = System.currentTimeMillis();         //先通过插件加载         loadRouterMap();         if (registerByPlugin) {             logger.info(TAG, "Load router map by arouter-auto-register plugin.");         } else { 			//加载routerMap             Set
      
        routerMap;             if (ARouter.debuggable() || PackageUtils.isNewVersion(context)) {                 logger.info(TAG, "Run with debug mode or new install, rebuild router map.");                 routerMap = ClassUtils.getFileNameByPackageName(mContext, ROUTE_ROOT_PAKCAGE);                 if (!routerMap.isEmpty()) {                     context.getSharedPreferences(AROUTER_SP_CACHE_KEY, Context.MODE_PRIVATE).edit().putStringSet(AROUTER_SP_KEY_MAP, routerMap).apply();                 }                 PackageUtils.updateVersion(context);             } else {                 logger.info(TAG, "Load router map from cache.");                 routerMap = new HashSet<>(context.getSharedPreferences(AROUTER_SP_CACHE_KEY, Context.MODE_PRIVATE).getStringSet(AROUTER_SP_KEY_MAP, new HashSet
       
        ()));             }             //开始加载             startInit = System.currentTimeMillis();             for (String className : routerMap) {                 if (className.startsWith(ROUTE_ROOT_PAKCAGE + DOT + SDK_NAME + SEPARATOR + SUFFIX_ROOT)) {                     // 加载ARouter$$RootXXX的IRouteRoot子类                     ((IRouteRoot) (Class.forName(className).getConstructor().newInstance())).loadInto(Warehouse.groupsIndex);                 } else if (className.startsWith(ROUTE_ROOT_PAKCAGE + DOT + SDK_NAME + SEPARATOR + SUFFIX_INTERCEPTORS)) {                     // 加载ARouter$$InterceptorsXXX的IInterceptorGroup子类                     ((IInterceptorGroup) (Class.forName(className).getConstructor().newInstance())).loadInto(Warehouse.interceptorsIndex);                 } else if (className.startsWith(ROUTE_ROOT_PAKCAGE + DOT + SDK_NAME + SEPARATOR + SUFFIX_PROVIDERS)) {                     // 加载ARouter$$ProvidersXXX的IProviderGroup子类                     ((IProviderGroup) (Class.forName(className).getConstructor().newInstance())).loadInto(Warehouse.providersIndex);                 }             }         }         logger.info(TAG, "Load root element finished, cost " + (System.currentTimeMillis() - startInit) + " ms.");         if (Warehouse.groupsIndex.size() == 0) {             logger.error(TAG, "No mapping files were found, check your configuration please!");         }         if (ARouter.debuggable()) {             logger.debug(TAG, String.format(Locale.getDefault(), "LogisticsCenter has already been loaded, GroupIndex[%d], InterceptorIndex[%d], ProviderIndex[%d]", Warehouse.groupsIndex.size(), Warehouse.interceptorsIndex.size(), Warehouse.providersIndex.size()));         }     } catch (Exception e) {         throw new HandlerException(TAG + "ARouter init logistics center exception! [" + e.getMessage() + "]");     } }复制代码

从com.alibaba.android.arouter.routes这个包下面去扫描并加载到routerMap，本地进行缓存，如果是debug模式或者是新版本都需要从新进行扫描。然后对router进行分类并加载到Warehouse中进行管理。

然后跟进_ARouter.afterInit方法

static void afterInit() {     interceptorService = (InterceptorService) ARouter.getInstance().build("/arouter/service/interceptor").navigation(); }复制代码

afterInit方法是跟使用Arouter跳转activity的代码非常像，它返回了一个InterceptorService进行赋值。跟进去看一下，ARouter.getInstance()返回了一个Arouter的单例对象，然后接着调用了它的build方法

public Postcard build(String path) {     return _ARouter.getInstance().build(path); }复制代码

接着又获取了_ARouter的单例对象并调用其build方法。

protected Postcard build(String path) {     if (TextUtils.isEmpty(path)) {         throw new HandlerException(Consts.TAG + "Parameter is invalid!");     } else {         PathReplaceService pService = ARouter.getInstance().navigation(PathReplaceService.class);         if (null != pService) {             path = pService.forString(path);         }         return build(path, extractGroup(path));     } }复制代码

对path进行了判空，接着用另一种navigation方法获取了一个PathReplaceService，这个我们后面再看。再接着就是调用了extractGroup方法从path中获取到路由的group，然后再调用build(String path, String group)方法。

protected Postcard build(String path, String group) { if (TextUtils.isEmpty(path) || TextUtils.isEmpty(group)) { throw new HandlerException(Consts.TAG + "Parameter is invalid!"); } else { PathReplaceService pService = ARouter.getInstance().navigation(PathReplaceService.class); if (null != pService) { path = pService.forString(path); } return new Postcard(path, group); } }

跟上面的build方法比较类似，最后就返回了一个postcart对象。afterInit方法中最后就是拿着返回的postcart对象去调用navigation方法，navigation方法最终会调用到_ARouter的navigation(final Context context, final Postcard postcard, final int requestCode, final NavigationCallback callback)方法。

protected Object navigation(final Context context, final Postcard postcard, final int requestCode, final NavigationCallback callback) {     try {         LogisticsCenter.completion(postcard);     } catch (NoRouteFoundException ex) {         logger.warning(Consts.TAG, ex.getMessage());         if (debuggable()) {             runInMainThread(new Runnable() {                 @Override                 public void run() {                     Toast.makeText(mContext, "There's no route matched!\n" +                             " Path = [" + postcard.getPath() + "]\n" +                             " Group = [" + postcard.getGroup() + "]", Toast.LENGTH_LONG).show();                 }             });         }         if (null != callback) {             callback.onLost(postcard);         } else {    // No callback for this invoke, then we use the global degrade service.             DegradeService degradeService = ARouter.getInstance().navigation(DegradeService.class);             if (null != degradeService) {                 degradeService.onLost(context, postcard);             }         }         return null;     }     if (null != callback) {         callback.onFound(postcard);     }     if (!postcard.isGreenChannel()) {   // It must be run in async thread, maybe interceptor cost too mush time made ANR.         interceptorService.doInterceptions(postcard, new InterceptorCallback() {             @Override             public void onContinue(Postcard postcard) {                 _navigation(context, postcard, requestCode, callback);             }             @Override             public void onInterrupt(Throwable exception) {                 if (null != callback) {                     callback.onInterrupt(postcard);                 }             }         });     } else {         return _navigation(context, postcard, requestCode, callback);     }     return null; }复制代码

代码比较多，我们看主要的，首先是调用了LogisticsCenter.completion(postcard)，这个方法是去加载路由信息，（前面LogisticsCenter只加载了相关group的一些东西，具体group中的路由还没有加载），如果已经加载就获取信息完成postcart对象其他字段的赋值。然后就是在拦截器中（如果是GreenChannel则直接调用）调用_navigation(context, postcard, requestCode, callback)方法。

public synchronized static void completion(Postcard postcard) {     if (null == postcard) {         throw new NoRouteFoundException(TAG + "No postcard!");     }     RouteMeta routeMeta = Warehouse.routes.get(postcard.getPath());     if (null == routeMeta) {    // Maybe its does't exist, or didn't load.         Class
       groupMeta = Warehouse.groupsIndex.get(postcard.getGroup());  // Load route meta.         if (null == groupMeta) {             throw new NoRouteFoundException(TAG + "There is no route match the path [" + postcard.getPath() + "], in group [" + postcard.getGroup() + "]");         } else {             try {                 IRouteGroup iGroupInstance = groupMeta.getConstructor().newInstance();                 iGroupInstance.loadInto(Warehouse.routes);                 Warehouse.groupsIndex.remove(postcard.getGroup());                 if (ARouter.debuggable()) {                     logger.debug(TAG, String.format(Locale.getDefault(), "The group [%s] has already been loaded, trigger by [%s]", postcard.getGroup(), postcard.getPath()));                 }             } catch (Exception e) {                 throw new HandlerException(TAG + "Fatal exception when loading group meta. [" + e.getMessage() + "]");             }             completion(postcard);   // Reload         }     } else {         postcard.setDestination(routeMeta.getDestination());         postcard.setType(routeMeta.getType());         postcard.setPriority(routeMeta.getPriority());         postcard.setExtra(routeMeta.getExtra());         Uri rawUri = postcard.getUri();         if (null != rawUri) {   // Try to set params into bundle.             Map
      
        resultMap = TextUtils.splitQueryParameters(rawUri);             Map
       
         paramsType = routeMeta.getParamsType();             if (MapUtils.isNotEmpty(paramsType)) {                 for (Map.Entry
        
          params : paramsType.entrySet()) {                     setValue(postcard,                             params.getValue(),                             params.getKey(),                             resultMap.get(params.getKey()));                 }                 postcard.getExtras().putStringArray(ARouter.AUTO_INJECT, paramsType.keySet().toArray(new String[]{}));             }             postcard.withString(ARouter.RAW_URI, rawUri.toString());         }         switch (routeMeta.getType()) {             case PROVIDER:                 Class
          providerMeta = (Class
         ) routeMeta.getDestination();                 IProvider instance = Warehouse.providers.get(providerMeta);                 if (null == instance) { // There's no instance of this provider                     IProvider provider;                     try {                         provider = providerMeta.getConstructor().newInstance();                         provider.init(mContext);                         Warehouse.providers.put(providerMeta, provider);                         instance = provider;                     } catch (Exception e) {                         throw new HandlerException("Init provider failed! " + e.getMessage());                     }                 }                 postcard.setProvider(instance);                 postcard.greenChannel();    // Provider should skip all of interceptors                 break;             case FRAGMENT:                 postcard.greenChannel();    // Fragment needn't interceptors             default:                 break;         }     } }复制代码

if (null == groupMeta)这段代码中就是将这个path对应的group中的路由全部加载进来，然后又一次调用了completion(postcard)方法，下面就是对postcard进行赋值，switch语句中可以看到PROVIDER、FRAGMENT就是直接不通过拦截器的，而且PROVIDER的创建由框架控制，如果有实例就不重复创建了。让后就是真正的路由方法_navigation(context, postcard, requestCode, callback)

private Object _navigation(final Context context, final Postcard postcard, final int requestCode, final NavigationCallback callback) {     final Context currentContext = null == context ? mContext : context;     switch (postcard.getType()) {         case ACTIVITY:             final Intent intent = new Intent(currentContext, postcard.getDestination());             intent.putExtras(postcard.getExtras());             int flags = postcard.getFlags();             if (-1 != flags) {                 intent.setFlags(flags);             } else if (!(currentContext instanceof Activity)) {    // Non activity, need less one flag.                 intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);             }             String action = postcard.getAction();             if (!TextUtils.isEmpty(action)) {                 intent.setAction(action);             }             runInMainThread(new Runnable() {                 @Override                 public void run() {                     startActivity(requestCode, currentContext, intent, postcard, callback);                 }             });             break;         case PROVIDER:             return postcard.getProvider();         case BOARDCAST:         case CONTENT_PROVIDER:         case FRAGMENT:             Class fragmentMeta = postcard.getDestination();             try {                 Object instance = fragmentMeta.getConstructor().newInstance();                 if (instance instanceof Fragment) {                     ((Fragment) instance).setArguments(postcard.getExtras());                 } else if (instance instanceof android.support.v4.app.Fragment) {                     ((android.support.v4.app.Fragment) instance).setArguments(postcard.getExtras());                 }                 return instance;             } catch (Exception ex) {                 logger.error(Consts.TAG, "Fetch fragment instance error, " + TextUtils.formatStackTrace(ex.getStackTrace()));             }         case METHOD:         case SERVICE:         default:             return null;     }     return null; }复制代码

简单明了，ACTIVITY就直接跳转了返回null，PROVIDER就返回provider的实现类，BOARDCAST、CONTENT_PROVIDER、FRAGMENT也是通过反射创建对应的实例对象然后返回。

从整个Arouter的初始化流程，大家应该就明白了，Arouter其实就是将类的相关信息与我们给定的路由形成一个映射，这些映射关系在Arouter初始化的时候被加载进来，然后再通过我们定义好的路由来找到我们的类。所以我们在组件化中就可以通过路由来跳转其他module的activity。