0.前言

我們在整合第三方SDK的時候大多都會在Application的onCreate方法裡進行SDK的初始化或配置工作，這好像也沒有什麼問題，不過我們能不能能做的更好一點呢？就是希望使用者在gradle檔案裡compile一下相應的庫就可以直接使用，不需要額外的初始化和配置.這個問題，我在閱讀Android Architecture Components（https://developer.android.com/topic/libraries/architecture/index.html） 原始碼時找到答案，現在把這個方案記錄下來。

1.註冊佔位的Provider

<provider

android:name="android.arch.lifecycle.LifecycleRuntimeTrojanProvider"
 

    android:authorities="com.example.android.persistence.lifecycle-trojan"
    android:exported="false"
    android:multiprocess="true" />

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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;
    }
}

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3.分析和總結

先說下結論：Provider的onCreate優先於Application的onCreate執行，並且此時的Application已經建立成功，而Provider裡的context正是Application的物件，完全符合需求。（也就是和在Application的onCreate裡是寫一樣一樣的）

LifecycleRuntimeTrojanProvider.onCreate的呼叫棧: 

Application.onCreate的呼叫棧： 

由ActivityThread的handleBindApplication方法可以看到，是先呼叫installContentProviders方法，然後呼叫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);
   }
}
}

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參考

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

本文轉自：http://blog.csdn.net/ihrthk/article/details/74025388