实现Android插件化的核心技术简介（三）：Android dynamic register activities

实现Android插件化的核心技术（三）：Android dynamic register activities

Android activities are monitored by Instrumentation.

Android activities受Instrumentation监控。

Each activity was started by Activity's startActivityForResult. (1)

由Activity的startActivityForResult方法启动，通过instrumentation的execStartActivity方法激活生命周期。

public void startActivityForResult(Intent intent, int requestCode, @Nullable Bundle options) {    if (mParent == null) {        Instrumentation.ActivityResult ar =            mInstrumentation.execStartActivity( // Override entry 1                this, mMainThread.getApplicationThread(), mToken, this,                intent, requestCode, options);        ...    }}

And instantiated by ActivityThread's performLaunchActivity. (2)

在ActivityThread的performLaunchActivity方法中通过instrumentation的newActivity方法实例化。

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {    ...    Activity activity = null;    try {        java.lang.ClassLoader cl = r.packageInfo.getClassLoader();        activity = mInstrumentation.newActivity( // Override entry 2                cl, component.getClassName(), r.intent);        StrictMode.incrementExpectedActivityCount(activity.getClass());        r.intent.setExtrasClassLoader(cl);        r.intent.prepareToEnterProcess();        if (r.state != null) {            r.state.setClassLoader(cl);        }    } catch (Exception e) {        if (!mInstrumentation.onException(activity, e)) {            throw new RuntimeException(                "Unable to instantiate activity " + component                + ": " + e.toString(), e);        }    }    ...}

To dynamic register activities, we register a stub activity in host's AndroidManifest.xml to cheat (1) to manager the activity life circle for us. And then cheat (2) to create the plugin activity instance.

动态注册Activity，首先在宿主manifest中注册一个命名特殊的占坑activity来欺骗(1)以获得生命周期，再欺骗(2)来获得插件activity实例。

So all the things to do is wrapper a instrumentation and replace the host one.

要做的就是封装一个instrumentation，替换掉宿主的。

Fake code:

<!-- Stub Activities --><activity android:name=".A.0" android:launchMode="standard"/>

ActivityThread thread = currentActivityThread();Instrumentation base = thread.@mInstrumentation;Instrumentation wrapper = new InstrumentationWrapper(base);thread.@mInstrumentation = wrapper;class InstrumentationWrapper extends Instrumentation {    public ActivityResult execStartActivity(..., Intent intent, ...) {        fakeToStub(intent);        base.execStartActivity(args);    }    @Override    public Activity newActivity(ClassLoader cl, String className, Intent intent) {        className = restoreToReal(intent, className);        return base.newActivity(cl, className, intent);    }}