前言

Android app开发中，经常会用到组件化技术，具体表现就是将各个模块以module的方式集成在主模块(App壳)中，各个业务module之间代码独立，互不依赖。那业务模块在不存在依赖关系的情况下，如何进行数据交互呢？这就涉及到模块间通讯了。网上有很多开源的模块间通讯方案，例如EventBus,ARouter等，今天来分析一下ARouter源码。

用法

• 环境配置
  build.gradle中添加依赖

    api config.thirddependencies.arouter_api
    annotationProcessor config.thirddependencies.arouter_compiler

• 在待启动的目标Activity添加注解

@Route(path = "/test/activity2")
public class Test2Activity extends AppCompatActivity {

    @Autowired
    String key1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test2);
    }
}

• 启动目标Activity

 ARouter.getInstance()
                       .build("/test/activity2")
                        .navigation();

源码分析

ARouter.getInstance()
.build("/test/activity2")调用的是_ARouter中的build方法,返回的是一个Postcard对象

/**
     * Build postcard by uri
     */
    protected Postcard build(Uri uri) {
        if (null == uri || TextUtils.isEmpty(uri.toString())) {
            throw new HandlerException(Consts.TAG + "Parameter invalid!");
        } else {
            PathReplaceService pService = ARouter.getInstance().navigation(PathReplaceService.class);
            if (null != pService) {
                uri = pService.forUri(uri);
            }
            return new Postcard(uri.getPath(), extractGroup(uri.getPath()), uri, null);
        }
    }

Postcard调用navigation()方法, 内部其实是调用_ARouter的navigation(),

/**
     * Use router navigation.
     *
     * @param context     Activity or null.
     * @param postcard    Route metas
     * @param requestCode RequestCode
     * @param callback    cb
     */
    protected Object navigation(final Context context, final Postcard postcard, final int requestCode, final NavigationCallback callback) {
        try {
            //首先对postcard进行一些处理，设置postcard的destination，type，priority 等一些属性值，completion()后面会有分析
            LogisticsCenter.completion(postcard);
        } catch (NoRouteFoundException ex) {
            logger.warning(Consts.TAG, ex.getMessage());

            if (debuggable()) {
                // Show friendly tips for user.
                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();
                    }
                });
            }
            // 如果处理postcard失败，通过 callback 回调失败结果
            // callback为空的情况下，如果有定义全局的降级处理（DegradeService），则使用全局处理
            //降级处理也需要我们自己实现DegradeService接口
            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;
        }
        //回调onFound
        if (null != callback) {
            callback.onFound(postcard);
        }

        //目前来说，PROVIDER服务类型，以及FRAGMENT类型不需要通过拦截器外，其他类型均需要通过拦截器
        if (!postcard.isGreenChannel()) {   // It must be run in async thread, maybe interceptor cost too mush time made ANR.
            //如果需要拦截就执行onInterrupt(),否则执行onContinue,在onContinue中执行_navigation
            interceptorService.doInterceptions(postcard, new InterceptorCallback() {
                /**
                 * Continue process
                 *
                 * @param postcard route meta
                 */
                @Override
                public void onContinue(Postcard postcard) {
                    _navigation(context, postcard, requestCode, callback);
                }

                /**
                 * Interrupt process, pipeline will be destory when this method called.
                 *
                 * @param exception Reson of interrupt.
                 */
                @Override
                public void onInterrupt(Throwable exception) {
                    if (null != callback) {
                        callback.onInterrupt(postcard);
                    }

                    logger.info(Consts.TAG, "Navigation failed, termination by interceptor : " + exception.getMessage());
                }
            });
        } else {
            return _navigation(context, postcard, requestCode, callback);
        }

        return null;
    }

在_ARouter的navigation方法中

• 调用 LogisticsCenter.completion(postcard);这个方法主要做数据加载处理，执行完这个方法后，目标activity的路由信息就已经设置到postCard对象中了
• 当调用 LogisticsCenter.completion(postcard)出现异常的时候，判断是NavigationCallback callback参数是否为空，callback不为空的话直接回调callback.onLost(); callback为空的话，调用全局降级服务DegradeService.onLost(), 然后终止整个流程
• 判断postcard.isGreenChannel()是否需要执行拦截器逻辑，在拦截器中如果需要拦截，则回调onInterrupt(Throwable exception)方法,不需要拦截则会回调onContinue(Postcard postcard), 在onContinue方法中执行_navigation方法取执行Activity跳转逻辑