写这篇文章的原因是昨天有个刚入门的小老弟问我ARouter的原理是怎样的。当时就把我搞不会了，当时我也不记得我以前有没有看过ARouter的源码。但是我还是老油条的回了一句“上百度找，网上很多都说得很清楚”，本以为这事就到处结束，结果他说网上别人写的他看得不是很懂。
那帮人帮到底，我只能带他慢慢过一遍ARouter，当然这篇文章肯定不会写得比较详细，因为我大致浏览下，能看到很多的关于ARouter的文章其实都写得很好，这是是为了更方便初学者，更慢的去过一遍ARouter
一. 简述ARouter原理
1. 为什么要使用ARouter
为什么要使用ARouter，无非就是做了组件化，如果module之间的相互引用，就会导致组件之间很混乱，使用ARouter能更好的实现解耦，并且让代码更可观。
2. ARouter的实现
我这边就只拿Activity举例。如果不使用ARouter，要在各个module之间做页面跳转。无非只能各个module之间相互引用，然后直接做Intent。要么使用隐式Intent等等，但这些方法都不太好。
ARouter的作用简单来说是在module之间不相互引用的基础上能实现显示Intent来跳转页面。
那么它是怎么实现的？很多新手其实卡在这里，既要不相互引用，又能使用显示Intent，这不相互矛盾吗？
其实不然，我们平时写Intent
Intent intent = new Intent(this, xxxx.class);
startActivity(intent)
加入在moduleA中写这段代码，但是xxxx是moduleB中的类，不应用的情况下肯定报红，你编译不过。
但其实这里的Intent构造方法是传的Class<?> 对象，所以我们可以不在这明确写xxxx.class。我可以在某个地方Class<?> cls = xxxx.class，然后传这个cls
ARouter的原理就是所有的moudle都引用ARouter，然后再moudle中去生成一个映射表，然后再把这个映射表传到ARouter中。如果还是不是很理解，可以先继续往下看
二. 源码分析
关于源码我这边只简单的讲一讲，详细的可以去网上找更细致的分析，我的目的主要是让大家了解大概的一个流程是怎样的
1. 映射表生成
我们一般配置ARouter会这样写
@Route(path = xxx/xxx)
public class xxx{
......
}
这个会在编译时生成一个文件，在build/intermediates/javac/....../classes/com/alibaba/....../routes/下，会看到一堆生成的.class文件
随便打开一个看看
看得出这就是一个映射表Map<String, RouteMeta>
某个module引用ARouter并且使用@Route注释的话都会生成一个这样的文件。
原理就在这里，想必猜都能猜得出，在ARouter中有提个Map<String, RouteMeta> 对象的映射表，然后在某个时候，会调用所有module中的这些文件的loadInto方法，把这个映射表传过来，做put操作。也就是下层的对象在上层传入Class<?>
如果到这里还是看不懂，建议多捋几次，这就是ARouter能实现module之间不引用的情况下又能实现显示Intent的办法。如果让你自己写一个ARouter框架，也是利用上面这招来弄。
2. 路由初始化
初始化调用
ARouter.init(context)
内部主要调用
hasInit = _ARouter.init(application);
if (hasInit) {
_ARouter.afterInit();
}
往下看，之后调用LogisticsCenter.init
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;
}
接着往下看，我把不重要的代码屏蔽掉
public synchronized static void init(Context context, ThreadPoolExecutor tpe) throws HandlerException {
......
try {
......
Set<String> routerMap;
// It will rebuild router map every times when debuggable.
if (ARouter.debuggable() || PackageUtils.isNewVersion(context)) {
logger.info(TAG, "Run with debug mode or new install, rebuild router map.");
// These class was generated by arouter-compiler.
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); // Save new version name when router map update finishes.
} 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<String>()));
}
logger.info(TAG, "Find router map finished, map size = " + routerMap.size() + ", cost " + (System.currentTimeMillis() - startInit) + " ms.");
startInit = System.currentTimeMillis();
for (String className : routerMap) {
if (className.startsWith(ROUTE_ROOT_PAKCAGE + DOT + SDK_NAME + SEPARATOR + SUFFIX_ROOT)) {
// This one of root elements, load root.
((IRouteRoot) (Class.forName(className).getConstructor().newInstance())).loadInto(Warehouse.groupsIndex);
} else if (className.startsWith(ROUTE_ROOT_PAKCAGE + DOT + SDK_NAME + SEPARATOR + SUFFIX_INTERCEPTORS)) {
// Load interceptorMeta
((IInterceptorGroup) (Class.forName(className).getConstructor().newInstance())).loadInto(Warehouse.interceptorsIndex);
} else if (className.startsWith(ROUTE_ROOT_PAKCAGE + DOT + SDK_NAME + SEPARATOR + SUFFIX_PROVIDERS)) {
// Load providerIndex
((IProviderGroup) (Class.forName(className).getConstructor().newInstance())).loadInto(Warehouse.providersIndex);
}
}
......
} catch (Exception e) {
throw new HandlerException(TAG + "ARouter init logistics center exception! [" + e.getMessage() + "]");
}
}
先判断版本号，PackageUtils.isNewVersion(context)，这里主要是做一个缓存的操作，第一次进来肯定进判断。
ClassUtils.getFileNameByPackageName(mContext, ROUTE_ROOT_PAKCAGE)方法是获取所有生成的com/alibaba/....../routes/下的class文件，如果还是不清楚，可以直接加个打印，就知道获取到的数组是什么了。
下面的for (String className : routerMap)循环，就是给这些文件分类，并调用loadInto方法来配置路由表（这个在上面就讲过），Warehouse这个类就是存放路由表的地方。
如果你细心，你会发现其实这里配置路由表的映射并不完整，因为没有给Warehouse的routes对象进行赋值，而我们的跳转的核心就是routes这个HashMap，没关系，我们继续往下看。
3. 路由跳转
看_ARouter.afterInit();的源码也行，看路由跳转的源码也行。
无非都是
ARouter.getInstance().build("xxxxxx").navigation()
build方法往下看
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));
}
}
这里正常流程pService会为空，直接执行build(path, extractGroup(path));
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);
}
}
还是为空，所以能看出这步最终是为了创建一个Postcard对象。
然后看navigation方法，我这边也把和流程无关紧要的代码屏蔽掉
protected Object navigation(final Context context, final Postcard postcard, final int requestCode, final NavigationCallback callback) {
......
try {
LogisticsCenter.completion(postcard);
} catch (NoRouteFoundException ex) {
......
}
if (null != callback) {
callback.onFound(postcard);
}
......
return _navigation(context, postcard, requestCode, callback);
return null;
}
关键在于 LogisticsCenter.completion(postcard);
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<? extends IRouteGroup> 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 {
// Load route and cache it into memory, then delete from metas.
try {
if (ARouter.debuggable()) {
logger.debug(TAG, String.format(Locale.getDefault(), "The group [%s] starts loading, trigger by [%s]", postcard.getGroup(), postcard.getPath()));
}
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<String, String> resultMap = TextUtils.splitQueryParameters(rawUri);
Map<String, Integer> paramsType = routeMeta.getParamsType();
if (MapUtils.isNotEmpty(paramsType)) {
// Set value by its type, just for params which annotation by @Param
for (Map.Entry<String, Integer> params : paramsType.entrySet()) {
setValue(postcard,
params.getValue(),
params.getKey(),
resultMap.get(params.getKey()));
}
// Save params name which need auto inject.
postcard.getExtras().putStringArray(ARouter.AUTO_INJECT, paramsType.keySet().toArray(new String[]{}));
}
// Save raw uri
postcard.withString(ARouter.RAW_URI, rawUri.toString());
}
switch (routeMeta.getType()) {
case PROVIDER: // if the route is provider, should find its instance
// Its provider, so it must implement IProvider
Class<? extends IProvider> providerMeta = (Class<? extends IProvider>) 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;
}
}
}
这里的代码都是有用的。RouteMeta routeMeta = Warehouse.routes.get(postcard.getPath());
上面说了，每给Warehouse.routes配置映射关系，所以第一次进来这里是为空，执行下面操作
IRouteGroup iGroupInstance = groupMeta.getConstructor().newInstance();
iGroupInstance.loadInto(Warehouse.routes);
Warehouse.groupsIndex.remove(postcard.getGroup());
简单来说就是把group中的映射关系转变为具体routes的映射关系，再调用一次自身completion赋值给Postcard
postcard.setDestination(routeMeta.getDestination());
postcard.setType(routeMeta.getType());
postcard.setPriority(routeMeta.getPriority());
postcard.setExtra(routeMeta.getExtra());
再接下来的switch (routeMeta.getType()) 中处理Type为PROVIDER和FRAGMENT的逻辑。
然后接着上面看_navigation方法
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:
// Build intent
final Intent intent = new Intent(currentContext, postcard.getDestination());
intent.putExtras(postcard.getExtras());
// Set flags.
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);
}
// Set Actions
String action = postcard.getAction();
if (!TextUtils.isEmpty(action)) {
intent.setAction(action);
}
// Navigation in main looper.
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;
}
我们一般写的跳转就是Type为ACTIVITY，能看到里面就是直接调用显示intent。
