无侵入进行SDK的初始化

0.前言

我们在集成第三方SDK的时候大多都会在Application的onCreate方法里进行SDK的初始化或配置工作，这好像也没有什么问题，不过我们能不能能做的更好一点呢？就是希望用户在gradle文件里compile一下相应的库就可以直接使用，不需要额外的初始化和配置.这个问题，我在阅读Android Architecture Components（https://developer.android.com/topic/libraries/architecture/index.html） 源码时找到答案，现在把这个方案记录下来。

1.注册占位的Provider

<providerandroid:name="android.arch.lifecycle.LifecycleRuntimeTrojanProvider"    android:authorities="com.example.android.persistence.lifecycle-trojan"    android:exported="false"    android:multiprocess="true" />

2.在Provider的onCreate初始化

public class LifecycleRuntimeTrojanProvider extends ContentProvider {    public LifecycleRuntimeTrojanProvider() {    }    public boolean onCreate() {        LifecycleDispatcher.init(this.getContext());        ProcessLifecycleOwner.init(this.getContext());        return true;    }    @Nullable    public Cursor query(@NonNull Uri uri, String[] strings, String s, String[] strings1, String s1) {        return null;    }    @Nullable    public String getType(@NonNull Uri uri) {        return null;    }    @Nullable    public Uri insert(@NonNull Uri uri, ContentValues contentValues) {        return null;    }    public int delete(@NonNull Uri uri, String s, String[] strings) {        return 0;    }    public int update(@NonNull Uri uri, ContentValues contentValues, String s, String[] strings) {        return 0;    }}

3.分析和总结

先说下结论：Provider的onCreate优先于Application的onCreate执行，并且此时的Application已经创建成功，而Provider里的context正是Application的对象，完全符合需求。（也就是和在Application的onCreate里是写一样一样的）

LifecycleRuntimeTrojanProvider.onCreate的调用栈:

Application.onCreate的调用栈：

由ActivityThread的handleBindApplication方法可以看到，是先调用installContentProviders方法，然后调用mInstrumentation.callApplicationOnCreate方法的。

public final class ActivityThread {private void handleBindApplication(AppBindData data) {    // Allow disk access during application and provider setup. This could   // block processing ordered broadcasts, but later processing would   // probably end up doing the same disk access.   final StrictMode.ThreadPolicy savedPolicy = StrictMode.allowThreadDiskWrites();   try {       // If the app is being launched for full backup or restore, bring it up in       // a restricted environment with the base application class.       Application app = data.info.makeApplication(data.restrictedBackupMode, null);       mInitialApplication = app;       // don't bring up providers in restricted mode; they may depend on the       // app's custom Application class       if (!data.restrictedBackupMode) {           if (!ArrayUtils.isEmpty(data.providers)) {               installContentProviders(app, data.providers);               // For process that contains content providers, we want to               // ensure that the JIT is enabled "at some point".               mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);           }       }       // Do this after providers, since instrumentation tests generally start their       // test thread at this point, and we don't want that racing.       try {           mInstrumentation.onCreate(data.instrumentationArgs);       }       catch (Exception e) {           throw new RuntimeException(               "Exception thrown in onCreate() of "               + data.instrumentationName + ": " + e.toString(), e);       }       try {           mInstrumentation.callApplicationOnCreate(app);       } catch (Exception e) {           if (!mInstrumentation.onException(app, e)) {               throw new RuntimeException(                   "Unable to create application " + app.getClass().getName()                   + ": " + e.toString(), e);           }       }   } finally {       StrictMode.setThreadPolicy(savedPolicy);   }}}

参考

* Android Architecture Components（https://developer.android.com/topic/libraries/architecture/index.html）