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Activity插件化原理第一种方案:Hook Instrumentation

人生一切难题,知识给你答案

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今天,我们来解决一个问题:

Activity插件化原理第一种方案:Hook Instrumentation

人生一切难题,知识给你答案。


Activity的插件化解决的一个根本性问题就是插件中的Activity并没有在宿主的AndroidManifest.xml中进行注册,也就是说我们需要启动一个未注册的Activity,因此需要对Activity的启动过程有个了解。

启动Activity时会请求AMS创建Activity,这里的AMS指的是ActivityManagerService,AMS所属的进程与宿主(发起者)不属于同一个进程,AMS位于SystemServer进程中。

未命名文件 (5).png

应用程序进程与AMS之间的通信是通过Binder来实现的,AMS要管理所有APP的启动请求,因此我们不能在SystemServer进程中进行相应的Hook,那么我们只能在应用进程中进行相应的Hook。

如果我们启动一个未注册的Activity,AMS会去检查AndroidManifest中是否注册了该Activity,如果未注册会报错。

未命名文件 (6).png

为了让AMS验证通过,需要启动一个预先在AndroidManifest中注册的Activity,我们称之为占坑,在启动插件Activity时替换为占坑Activity,达到一个欺上瞒下的作用,当AMS验证通过之后,需要将启动的占坑Activity替换为插件Activity。

未命名文件 (8).png

总结下来Activity的插件化需要做两件事:

  • 将请求启动的插件Activity替换为占坑Activity。
  • 绕过AMS验证后,将占坑Activity替换为插件Activity。

什么时候将插件Activity替换为占坑Activity?又是什么时候还原插件Activity?这需要我们对Activity的启动流程有个相应的认识。

我们在Activity中调用startActivity方法如下:

    @Override
    public void startActivity(Intent intent) {
        this.startActivity(intent, null);
    }
    
        @Override
    public void startActivity(Intent intent, @Nullable Bundle options) {
        if (options != null) {
           startActivityForResult(intent, -1, options);
        } else {
           startActivityForResult(intent, -1);
        }
    }
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调用startActivityForResult方法:

    public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
            @Nullable Bundle options) {
        if (mParent == null) {
            //Activity启动
            options = transferSpringboardActivityOptions(options);
            Instrumentation.ActivityResult ar =
                mInstrumentation.execStartActivity(
                    this, mMainThread.getApplicationThread(), mToken, this,
                    intent, requestCode, options);
            if (ar != null) {
                mMainThread.sendActivityResult(
                    mToken, mEmbeddedID, requestCode, ar.getResultCode(),
                    ar.getResultData());
            }
            if (requestCode >= 0) {
                mStartedActivity = true;
            }

            cancelInputsAndStartExitTransition(options);
            windows.
        } else {
            if (options != null) {
                mParent.startActivityFromChild(this, intent, requestCode, options);
            } else {
                mParent.startActivityFromChild(this, intent, requestCode);
            }
        }
    }

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startActivityForResult方法中通过调用mInstrumentation的execStartActivity方法来启动Activity,这个mInstrumentation是Activity的成员变量,在ActivityThread的performLaunchActivity方法中通过Activity的attach方法传入,同时Activity的创建也是在performLaunchActivity方法中创建的,通过mInstrumentation.newActivity。

//:/frameworks/base/core/java/android/app/ActivityThread.java
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
    ...
    try {
        java.lang.ClassLoader cl = appContext.getClassLoader();
        activity = mInstrumentation.newActivity(
                    cl, component.getClassName(), r.intent);
        StrictMode.incrementExpectedActivityCount(activity.getClass());
        r.intent.setExtrasClassLoader(cl);
        r.intent.prepareToEnterProcess();
        if (r.state != null) {
            r.state.setClassLoader(cl);
        }
    }
    ...
    activity.attach(appContext, this, getInstrumentation(), r.token,
                        r.ident, app, r.intent, r.activityInfo, title, r.parent,
                        r.embeddedID, r.lastNonConfigurationInstances, config,
                        r.referrer, r.voiceInteractor, window, r.configCallback);
    ...
}
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综上所述Instrumentation提供了execStartActivity方法来启动Activity,newActivity方法来创建Activity。因此,第一种方案就是用代理Instrumentation来替代Activity的Instrumentation,并在代理Instrumentation的execStartActivity方法中替换为占坑Activity,在newActivity方法还原插件Activity。

现在我们基于第一种方案Hook Instrumentation来实现Activity的插件化。

首先创建占坑Activity:

public class StubActivity extends AppCompatActivity {

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_stub);
    }
}
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创建插件Activity:

public class TargetActivity extends AppCompatActivity {

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_target);
    }
}
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并在AndroidManifest.xml中注册占坑Activity:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.glh.haiproject01">

    <application
        android:name=".MyApplication"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme"
        tools:ignore="AllowBackup,GoogleAppIndexingWarning">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".StubActivity" />
    </application>

</manifest>
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在AndroidManifest.xml中没有注册插件Activity,这时如果启动插件Activity会报错。

最后Hook Instrumentation,将ActivityThread中的成员变量Instrumentation替换成代理的Instrumentation。

创建代理Instrumentation类:

public class InstrumentationProxy extends Instrumentation {

    private Instrumentation mInstrumentation;
    private PackageManager mPackageManager;

    public InstrumentationProxy(Instrumentation instrumentation, PackageManager packageManager) {
        this.mInstrumentation = instrumentation;
        this.mPackageManager = packageManager;
    }

    public ActivityResult execStartActivity(
            Context who, IBinder contextThread, IBinder token, Activity target,
            Intent intent, int requestCode, Bundle options) {

        List<ResolveInfo> resolveInfo = mPackageManager.queryIntentActivities(intent, PackageManager.MATCH_ALL);
        //判断启动的插件Activity是否在AndroidManifest.xml中注册过
        if (null == resolveInfo || resolveInfo.size() == 0) {
            //保存目标插件
            intent.putExtra(HookHelper.REQUEST_TARGET_INTENT_NAME, intent.getComponent().getClassName());
            //设置为占坑Activity
            intent.setClassName(who, "com.glh.haiproject01.StubActivity");
        }

        try {
            Method execStartActivity = Instrumentation.class.getDeclaredMethod("execStartActivity",
                    Context.class, IBinder.class, IBinder.class, Activity.class,
                    Intent.class, int.class, Bundle.class);
            return (ActivityResult) execStartActivity.invoke(mInstrumentation, who, contextThread, token, target, intent, requestCode, options);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
        return null;
    }

    public Activity newActivity(ClassLoader cl, String className, Intent intent) throws InstantiationException,
            IllegalAccessException, ClassNotFoundException {
        String intentName=intent.getStringExtra(HookHelper.REQUEST_TARGET_INTENT_NAME);
        if(!TextUtils.isEmpty(intentName)){
            return super.newActivity(cl,intentName,intent);
        }
        return super.newActivity(cl,className,intent);
    }

}
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代理类InstrumentationProxy的execStartActivity方法先判断插件Activity是否在AndroidManifest.xml中注册过,如果没有注册过就需要替换占坑的Activity,在newActivity方法中还原插件Activity。

代理类InstrumentationProxy写完后,需要对ActivityThread的成员变量mInstrumentation进行替换。

public class MyApplication extends Application {

    @Override
    protected void attachBaseContext(Context base) {
        super.attachBaseContext(base);
        hookActivityThreadInstrumentation();
    }


    private void hookActivityThreadInstrumentation(){
        try {
            Class<?> activityThreadClass=Class.forName("android.app.ActivityThread");
            Field activityThreadField=activityThreadClass.getDeclaredField("sCurrentActivityThread");
            activityThreadField.setAccessible(true);
            //获取ActivityThread对象sCurrentActivityThread
            Object activityThread=activityThreadField.get(null);

            Field instrumentationField=activityThreadClass.getDeclaredField("mInstrumentation");
            instrumentationField.setAccessible(true);
            //从sCurrentActivityThread中获取成员变量mInstrumentation
            Instrumentation instrumentation= (Instrumentation) instrumentationField.get(activityThread);
            //创建代理对象InstrumentationProxy
            InstrumentationProxy proxy=new InstrumentationProxy(instrumentation,getPackageManager());
            //将sCurrentActivityThread中成员变量mInstrumentation替换成代理类InstrumentationProxy
            instrumentationField.set(activityThread,proxy);
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}
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这时我们在主界面点击跳转插件Activity:

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        findViewById(R.id.btn_startActivity).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(MainActivity.this,TargetActivity.class);
                startActivity(intent);
            }
        });
    }
}
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运行效果:

wq1.gif


838794-506ddad529df4cd4.webp.jpg

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