Application.onCreate 、ContentProvider.onCreate 、 Activity.onCreate 的调用顺序研究

网上看到的一个问题，一开始没想到答案，也是很懵的，于是自己写了个 demo 。在 demo 里打印 log 顺序。先说结果吧

Application.attachBaseContext();
ContentProvider.onCreate();
Application.onCreate();
Activity.onCreate();

一开始，我以为是 Application.onCreate() -> ContentProvider.onCreate() -> Activity.onCreate() 的顺序的。

于是很费解，就找了源码看看。

private void handleBindApplication(AppBindData data) {
 // 省略代码
 // If the app is being launched for full backup or restore, bring it up in
 // a restricted environment with the base application class.
 // 1 这里是开始创建 Application , 然后调用 attachBaseContext() 方法
 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)) {
 // 2 开始初始化 ContentProvider ,
 // 个人的理解是防止自定义的 Application 需要使用 ContentProvider 的时候 ContentProvider 没有初始化
 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 {
 // 3 这里调用 Application 的 onCreate() 方法
 mInstrumentation.callApplicationOnCreate(app);
 } catch (Exception e) {
 if (!mInstrumentation.onException(app, e)) {
 throw new RuntimeException(
 "Unable to create application " + app.getClass().getName()
 + ": " + e.toString(), e);
 }
 }
 
 // 省略代码
 
}

看代码的确是这样

ContentProvider.onCreate() -> Application.onCreate() -> Activity.onCreate()

为什么是这样，想了想，可能是防止开发者在自定义的 Application 的 onCreate 方法里面使用 ContentProvider 的时候 ContentProvider 没有初始化导致错误吧。