本文主要是介绍【Android插件化】启动没有在Manifest中注册的Activity，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
1 概述
如果要启动没有在Manifest中注册的Activity，应该从startActivity着手。一般启动Activity的方式有两种，一种是startActivity，一种是startActivityForResult。其实startActivity最终调用的也是startActivityForResult，如下所示：
//Activity.java@Overridepublic void startActivity(Intent intent, @Nullable Bundle options) {if (options != null) {startActivityForResult(intent, -1, options);} else {// Note we want to go through this call for compatibility with// applications that may have overridden the method.startActivityForResult(intent, -1);}}
当我们启动一个Activity时，AMS会对这个Activity是否在AndroidManifest中声明注册进行检查，如果没有注册，则会报错。要想启动没有在AndroidManifest中注册的Activity，则需要“欺骗AMS”，让其以为我们已经在AndroidManifest中注册了。
基本思路是：
- 发送要启动的Activity信息给AMS之前，把这个Activity替换为一个在AndroidManifest中声明的StubActivity，这样就能绕过AMS的检查，在替换过程中，要把原来的Activity信息保存起来。
- AMS通知App启动StubActivity时，我们再将保存的Activity替换StubActivity，这样就能启动没有在AndroidManifest中注册的Activity。
修改Activity启动流程如图所示（图片来自网络）
2 代码实现
AndroidManifest.xml
<applicationandroid:name=".MainApplication"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"><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=".SubActivity"/></application>
一共两个Activity，分别是MainActivity和SubActivity，一个MainApplication，SubActivity是一个壳Activity，用于欺骗AMS的。
MainActivity.java
private View.OnClickListener mListener = new View.OnClickListener() {@Overridepublic void onClick(View v) {Intent intent = new Intent();intent.setClass(MainActivity.this, PluginTestActivity.class);startActivity(intent);}};
PluginTestActivity并没有在AndroidManifest中注册，正常情况下会报错，所以我们需要欺骗AMS。
欺骗AMS的方式有几种，这里我们选择对ActivityThread的mInstrumentation进行hook。代码如下：
public class HookHelper {public static final String PLUGIN_INTENT = "plugin_intent";public static void hookInstrumentation(Context context,String className) throws Exception{//获取ActivityThread的字节码对象Class<?> clazz = Class.forName("android.app.ActivityThread");//获取ActivityThread中的sCurrentActivityThread字段Field sCurrentActivityThreadField = ReflectUtils.getField(clazz,"sCurrentActivityThread");//获取ActivityThread中的mInstrumentation字段Field mInstrumentationField = ReflectUtils.getField(clazz,"mInstrumentation");//获取ActivityThread中的sCurrentActivityThread的值并赋值给currentActivityThreadObject currentActivityThread = sCurrentActivityThreadField.get(clazz);//获取ActivityThread中的mInstrumentation的值并赋值给instrumentationInstrumentation instrumentation = (Instrumentation) mInstrumentationField.get(currentActivityThread);//创建一个PackageManager对象packageManagerPackageManager packageManager = context.getPackageManager();//创建InstrumentationProxy对象，InstrumentationProxy是继承Instrumentation的类，下面详细介绍InstrumentationProxy instrumentationProxy = new InstrumentationProxy(instrumentation,packageManager,className);//将ActivityThread中的mInstrumentation赋值为instrumentationProxyReflectUtils.setFieldObject(clazz,currentActivityThread,"mInstrumentation",instrumentationProxy);}
}
InstrumentationProxy类如下
package com.example.plugintest;import android.app.Activity;
import android.app.Instrumentation;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.content.pm.ResolveInfo;
import android.os.Bundle;
import android.os.IBinder;
import android.text.TextUtils;import java.lang.reflect.Method;
import java.util.List;/*** Created by yds* on 2020/2/14.*/
public class InstrumentationProxy extends Instrumentation{private Instrumentation mInstrumentation;private PackageManager mPackageManager;private String className;public InstrumentationProxy(Instrumentation mInstrumentation, PackageManager mPackageManager, String className) {this.mInstrumentation = mInstrumentation;this.mPackageManager = mPackageManager;this.className = className;}public ActivityResult execStartActivity(Context who, IBinder contextThread, IBinder token, Activity target,Intent intent, int requestCode, Bundle options) {List<ResolveInfo> infos = mPackageManager.queryIntentActivities(intent, PackageManager.MATCH_ALL);if (infos == null || infos.size() == 0) {intent.putExtra(HookHelper.PLUGIN_INTENT,intent.getComponent().getClassName());intent.setClassName(who,className);}try {Method execMethod = Instrumentation.class.getDeclaredMethod("execStartActivity",Context.class,IBinder.class,IBinder.class,Activity.class,Intent.class,int.class,Bundle.class);return (ActivityResult) execMethod.invoke(mInstrumentation,who,contextThread,token,target,intent,requestCode,options);} catch (Exception e) {e.printStackTrace();}return null;}public Activity newActivity(ClassLoader cl,String className,Intent intent) throwsInstantiationException,IllegalAccessException,ClassNotFoundException{String intentName = intent.getStringExtra(HookHelper.PLUGIN_INTENT);if(!TextUtils.isEmpty(intentName)){return super.newActivity(cl,intentName,intent);}return super.newActivity(cl,className,intent);}
}只要将InstrumentationProxy赋值给ActivityThread的mInstrumentation，调用startActivity时，最终会调用InstrumentationProxy的execStartActivity和newActivity。我们只要在execStartActivity中将未注册的Activity保存起来，并使用已注册的SubActivity，然后在newActivity中将保存起来未注册的Activity替换SubActivity就可以了。
源码地址：https://github.com/Yedongsheng/PluginTest01
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