How to solve the problem of Router cross-module jump

After starting a modular development project, a very important issue is the page jump problem. This article mainly introduces the example of Router solving the page jump under cross-module. Now I will share it with you and give you an example. refer to.

1. Foreword

After starting a modular development project, a very important issue is the page jump problem.

For details on modular development, please see my other article Android Modular Development Exploration.

It is precisely because the project is divided into modules that there is no dependency between the modules and they are invisible to each other. So what should we do if we jump from interface a of module A to interface b of module B?

2. Cross-module jump methods

Here we will first introduce these common jump methods:

1. Show jump

2. Implicit jump

3. Scheme protocol jump

4. ##Router Routing table solution

2.1 Display jump

Display jump is our most commonly used jump method: using Intent, passing in the current Activity context, and the class object of the target Activity are enough, as follows:

Intent intent = new Intent();
intent.setClass(mContext, GuideActivity.class);
startActivity(intent);

Obviously, this method can only be called when the target Activity is visible (Activity is under the same Module). Not suitable for jumping between modules.

2.2 Hidden jump

The hidden jump we are talking about here is that the intent does not set a class, but sets an Action or Category.

For example:

In the manifest file

<!--网页展示界面-->
<activity
  android:name="com.whaty.base.BaseWebViewActivity"
  android:hardwareAccelerated="true">
    <intent-filter>
      <category android:name="android.intent.category.DEFAULT" />
      <action android:name="com.whaty.base.BaseWebViewActivity" />
    </intent-filter>
</activity>

When jumping:

//创建一个隐式的 Intent 对象：Action 动作 
Intent intent = new Intent(); 
//设置 Intent 的动作为清单中指定的action 
intent.setAction("com.whaty.base.BaseWebViewActivity"); 
startActivity(intent);

2.3 scheme jump

If we define a URI for B page - wsc://home/bbb, and then serialize the shared messageModel into a Json string, then A only needs to assemble a jump protocol that conforms to the B page scheme. wsc://home/bbb?message={ “name”:”John”, “age”:31, “city”:”New York” }

In the manifest file, configure the data attribute and set Its host, path, scheme, etc.

<activity android:name=".ui.BbbActivity"
  <intent-filter>
    <category android:name="android.intent.category.DEFAULT" />
    <action android:name="android.intent.action.VIEW" />
    <data
      android:host="bbb"
      android:path="/home"
      android:scheme="wsc" />
  </intent-filter>
</activity>

When jumping:

final Uri uri = new Uri.Builder().authority("wsc").path("home/bbb").appendQueryParameter("message", new Gson().toJson(messageModel)).build();
final Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setData(uri);
startActivity(intent);

The above methods are not what we want. Next, we will introduce our Router solution.

3. Why use Router

Google provides two native routing solutions: explicit and implicit. However, in modular development, explicit Intent has the problem of direct dependence on classes, causing severe coupling between modules. Implicit Intent requires a large number of paths to be configured in the Manifest, making it difficult to expand (such as jump interception). In order to solve the above problems, we need to adopt a more flexible Router solution.

4. Implementation Ideas

The idea is as follows:

Use annotations to label aliases for each target Activity. When the application starts, all classes are scanned and the annotated activities are stored in the routing table.

When jumping, obtain the class object of the target Activity through the alias in the routing table, and use Intent to implement the jump.

5. Code implementation

5.1 Custom annotations

/**
 * Description: 路由跳转界面 注解
 * Created by jia on 2018/1/10.
 * 人之所以能，是相信能
 */
@Target(ElementType.TYPE) //注解作用于类型（类，接口，注解，枚举）
@Retention(RetentionPolicy.RUNTIME) //运行时保留，运行中可以处理
@Documented // 生成javadoc文件
public @interface Action {

  String DEFAULT = "js";

  String value() default DEFAULT;

}

For a detailed introduction to custom annotations, Please read my article Java Advanced Custom Annotations. No more to say here.

5.2 Annotate Activity

@Action("MainActivity")
public class MainActivity extends BaseActivity implements TabLayout.OnTabSelectedListener {

  ...
}

When creating an Activity, annotate it with the just customized annotation and annotate it with an alias.

5.3 Scanning at startup

private void getAllActivities(Context ctx){
  try {
    //通过资源路径获得DexFile
    DexFile e = new DexFile(ctx.getPackageResourcePath());
    Enumeration entries = e.entries();
    //遍历所有元素
    while(entries.hasMoreElements()) {
      String entryName = (String)entries.nextElement();
      //匹配Activity包名与类名
      if(entryName.contains("activity") && entryName.contains("Activity")) {
        //通过反射获得Activity类
        Class entryClass = Class.forName(entryName);
        if(entryClass.isAnnotationPresent(Action.class)) {
          Action action = (Action)entryClass.getAnnotation(Action.class);
          this.map.put(action.value(), entryClass);
        }
      }
    }
  } catch (Exception e) {
    e.printStackTrace();
  }
}

When the application starts, all classes under the package are scanned in Application. First, find the activity in the name (defined under the activity package), and then Activities marked with annotations are stored in the map.

5.4 Jump

/**
 * 页面跳转
 * @param activity
 * @param alias
 */
public void jumpActivity(Activity activity, String alias) throws ClassNotFoundException{
  if(map.containsKey(alias)) {
    Intent intent = new Intent(activity, map.get(alias));
    activity.startActivity(intent);
  } else {
    throw new ClassNotFoundException();
  }
}

Just pass in the alias of the target Activity when jumping (the alias here is the alias of the annotation).

Summary

In this way, the module dependency problem caused by jumping Activity is solved. Compared with the native solution, it is more scalable. However, this plan is only phased and there are still some problems. First of all, frequent use of reflection during the loading process will cause performance problems. Secondly, the alias of each Activity needs to be maintained uniformly, which increases the cost of collaboration. Still needs to be optimized.

Of course, there are many popular Router solutions on the market (such as Alibaba’s ARouter). Here is just an idea. If you have good suggestions, welcome to exchange and make progress together.

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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