滴滴开源Android插件化框架VirtualAPK原理分析

Android , 评论

概述

滴滴出行公司的首个对外开源项目 - VirtualAPK。地址：https://github.com/didi/VirtualAPK

滴滴自行研发了这款插件化框架，功能全面、兼容性好，还能够适用于有耦合的业务插件，这就是VirtualAPK存在的意义。业内认为，在加载耦合插件方面，VirtualAPK可以说是开源方案的首选。据说滴滴打车里面已经用上了，所以还是有必要一探究竟的~~

VirtualAPK 的工作流程如图所示：

VirtualAPK 对于插件没有额外的约束，原生的 apk 即可作为一个插件。插件工程编译生成 apk 后，通过宿主 App 加载，每个插件 apk 被加载后，都会在宿主中创建一个单独的 LoadedPlugin 对象。如上图所示，通过这些 LoadedPlugin 对象，VirtualAPK 就可以管理插件并赋予插件新的意义，使其可以像手机中安装过的App一样运行。

Activity 支持

Hook ActivityManagerService

插件化支持首先要解决的一点就是插件里的Activity并未在宿主程序的 AndroidMainfest.xml 注册，常规方法肯定无法直接启动插件的Activity，这个时候就需要去了解Activity的启动流程，关于启动过程主要的几个步骤请参考：浅析Android Activity的启动过程

从上文中可知，Activity 启动实际上是调用了 Instrumentation.execStartActivity 这个方法。源码如下：

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public ActivityResult execStartActivity(Context who, IBinder contextThread, IBinder token, Activity target,  
            Intent intent, int requestCode, Bundle options) {  
    IApplicationThread whoThread = (IApplicationThread) contextThread;  
    if (mActivityMonitors != null) {  
        synchronized (mSync) {  
            final int N = mActivityMonitors.size();  
            for (int i=0; i<N; i++) { //先查找一遍看是否存在这个activity  
                final ActivityMonitor am = mActivityMonitors.get(i);  
                if (am.match(who, null, intent)) {  
                    am.mHits++;  
                    if (am.isBlocking()) {  
                        return requestCode >= 0 ? am.getResult() : null;  
                    }  
                    break;  
                }  
            }  
        }  
    }  
    try {  
        intent.migrateExtraStreamToClipData();  
        intent.prepareToLeaveProcess();  
        //这里才是真正打开activity的地方，其核心功能在whoThread中完成。  
        int result = ActivityManagerNative.getDefault().startActivity(whoThread, who.getBasePackageName(), intent,  
                    intent.resolveTypeIfNeeded(who.getContentResolver()),token, target != null ? target.mEmbeddedID : null,  
                    requestCode, 0, null, options);         
        checkStartActivityResult(result, intent); // 处理各种异常，如ActivityNotFound  
    } catch (RemoteException e) {  
    }  
    return null;  
}

可见， startActivity 最终通过 ActivityManagerNative.getDefault() 远程调用了AMS的startActivity方法， ActivityManagerNative 实际上就是 ActivityManagerService 这个远程对象的 Binder 代理对象，每次需要与AMS交互时，需要通过这个 Binder 对象完成远程IPC调用。

还不了解Binder的童鞋，可以看看老罗的Android进程间通信（IPC）机制Binder简要介绍和学习计划

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// ActivityManagerNative.getDefault()
static public IActivityManager getDefault() {
    return gDefault.get();
}

private static final Singleton<iactivitymanager> gDefault = 
    new Singleton<iactivitymanager>() {
           protected IActivityManager create() {
               IBinder b = ServiceManager.getService("activity");
               if (false) {
                   Log.v("ActivityManager", "default service binder = " + b);
               }
               IActivityManager am = asInterface(b);
               if (false) {
                   Log.v("ActivityManager", "default service = " + am);
               }
               return am;
           }
};


从这我们可以知道，ActivityManagerNative.getDefault() 实际上是返回了一个 IActivityManager 的单例对象。

那么，VirtualApk 所要做的第一件事，就是把这个 AMS 代理对象保存起来。首先，我们可以看一下 VirtualApk 核心库里面 com.didi.virtualapk.PluginManager 这个类的初始化：

```java

// 构造方法
private PluginManager(Context context) {
    Context app = context.getApplicationContext();
    if (app == null) {
        this.mContext = context;
    } else {
        this.mContext = ((Application)app).getBaseContext();
    }
    prepare();
}

// 初始化
private void prepare() {
    Systems.sHostContext = getHostContext();
    this.hookInstrumentationAndHandler();
    this.hookSystemServices();
}

/**
 * Hook 出一个IActivityManager，也就是 AMS 的代理对象
 */
private void hookSystemServices() {
    try {
        // 反射调用 ActivityManagerNative.getDefault()，实际上这在6.0中是公开的静态方法，反射可能是考虑到版本兼容性吧？
        Singleton<IActivityManager> defaultSingleton = (Singleton<IActivityManager>) ReflectUtil.getField(ActivityManagerNative.class, null, "gDefault");
        // 通过动态代理的方式去创建代理对象，之后所有ActivityManagerNative中的方法被调用的时候都会经过这个代理
        IActivityManager activityManagerProxy = ActivityManagerProxy.newInstance(this, defaultSingleton.get());

        // Hook IActivityManager from ActivityManagerNative，实际上就是把 ActivityManagerNative 替换为刚创建的 activityManagerProxy
        ReflectUtil.setField(defaultSingleton.getClass().getSuperclass(), defaultSingleton, "mInstance", activityManagerProxy);

        if (defaultSingleton.get() == activityManagerProxy) {
            // 两者一样，保存下来
            this.mActivityManager = activityManagerProxy;
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

实际上除了 startActivity 是调用 AMS 的方法以外，startService， bindService 等方法，最终调用到AMS的里的方法，这个我们在动态代理类 com.didi.virtualapk.delegate.ActivityManagerProxy 也可以找到：

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@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if ("startService".equals(method.getName())) {
        try {
            // 执行自定义的 startService 过程，后面会提到
            return startService(proxy, method, args);
        } catch (Throwable e) {
            Log.e(TAG, "Start service error", e);
        }
    } else if ("stopService".equals(method.getName())) {
        try {
            return stopService(proxy, method, args);
        } catch (Throwable e) {
            Log.e(TAG, "Stop Service error", e);
        }
    } else if ("stopServiceToken".equals(method.getName())) {
        try {
            return stopServiceToken(proxy, method, args);
        } catch (Throwable e) {
            Log.e(TAG, "Stop service token error", e);
        }
    } else if ("bindService".equals(method.getName())) {
        try {
            return bindService(proxy, method, args);
        } catch (Throwable e) {
            e.printStackTrace();
        }
    } else if ("unbindService".equals(method.getName())) {
        try {
            return unbindService(proxy, method, args);
        } catch (Throwable e) {
            e.printStackTrace();
        }
    } else if ("getIntentSender".equals(method.getName())) {
        try {
            getIntentSender(method, args);
        } catch (Exception e) {
            e.printStackTrace();
        }
    } else if ("overridePendingTransition".equals(method.getName())){
        try {
            overridePendingTransition(method, args);
        } catch (Exception e){
            e.printStackTrace();
        }
    }

    try {
        // sometimes system binder has problems.
        return method.invoke(this.mActivityManager, args);
    } catch (Throwable th) {
        Throwable c = th.getCause();
        if (c != null && c instanceof DeadObjectException) {
            // retry connect to system binder
            IBinder ams = ServiceManager.getService(Context.ACTIVITY_SERVICE);
            if (ams != null) {
                IActivityManager am = ActivityManagerNative.asInterface(ams);
                mActivityManager = am;
            }
        }

        Throwable cause = th;
        do {
            if (cause instanceof RemoteException) {
                throw cause;
            }
        } while ((cause = cause.getCause()) != null);

        throw c != null ? c : th;
    }

}

所以实际上就等同于我们重写了一些 Activity、Service 的相关操作。具体做些什么，后面会提到~

Hook Instrumentation

回过头去看看 Instrumentation.execStartActivity 这个方法，在最后有这么一句代码：

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checkStartActivityResult(result, intent); // 处理各种异常，如ActivityNotFound
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static void checkStartActivityResult(int res, Object intent) {  
    if (res >= ActivityManager.START_SUCCESS) {  
        return;  
    }  
      
    switch (res) {  
        case ActivityManager.START_INTENT_NOT_RESOLVED:  
        case ActivityManager.START_CLASS_NOT_FOUND:  
            if (intent instanceof Intent && ((Intent)intent).getComponent() != null)  
                throw new ActivityNotFoundException(  
                        "Unable to find explicit activity class "  
                        + ((Intent)intent).getComponent().toShortString()  
                        + "; have you declared this activity in your AndroidManifest.xml?");  
            throw new ActivityNotFoundException(  
                    "No Activity found to handle " + intent);  
        case ActivityManager.START_PERMISSION_DENIED:  
            throw new SecurityException("Not allowed to start activity "  
                    + intent);  
        case ActivityManager.START_FORWARD_AND_REQUEST_CONFLICT:  
            throw new AndroidRuntimeException(  
                    "FORWARD_RESULT_FLAG used while also requesting a result");  
        case ActivityManager.START_NOT_ACTIVITY:  
            throw new IllegalArgumentException(  
                    "PendingIntent is not an activity");  
        default:  
            throw new AndroidRuntimeException("Unknown error code "  
                    + res + " when starting " + intent);  
    }  
}

相信大家对上面的这些异常信息不陌生吧，其中最熟悉的非 Unable to find explicit activity class 莫属了，如果 Activity 没有在 AndroidMainfest.xml 注册，将会抛出此异常。

那么就得思考一个问题了，插件的 Activity 并未在宿主程序的 AndroidMainfest.xml 注册，要如何才能绕过这一层检测？

前文中提到，com.didi.virtualapk.PluginManager 这个类的初始化的时候，除了 Hook 出一个 AMS 代理对象以外，还 Hook 出一个 Instrumentation 对象。代码如下：

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private void hookInstrumentationAndHandler() {
    try {
        Instrumentation baseInstrumentation = ReflectUtil.getInstrumentation(this.mContext);
        if (baseInstrumentation.getClass().getName().contains("lbe")) {
            // reject executing in paralell space, for example, lbe.
            System.exit(0);
        }

        // 创建自定义的 instrumentation，重写了 newActivity() 等一些方法
        // baseInstrumentation 后面还会用到，也保存下来
        final VAInstrumentation instrumentation = new VAInstrumentation(this, baseInstrumentation);
        
        // 获取 ActivityThread 的实例
        Object activityThread = ReflectUtil.getActivityThread(this.mContext);
        
        // 用自定义的 instrumentation 替换掉 ActivityThread 里面的 instrumentation
        ReflectUtil.setInstrumentation(activityThread, instrumentation);
        ReflectUtil.setHandlerCallback(this.mContext, instrumentation);
        this.mInstrumentation = instrumentation;
    } catch (Exception e) {
        e.printStackTrace();
    }
}

既然 Activity 的启动，中间走了 Instrumentation.execStartActivity 这个方法，那么我们大概可以知道，Hook 出一个 Instrumentation 对象用来做什么了，实际上就是用来帮助启动插件的 Activity。

启动插件Activity

我们 Hook 了一个 VAInstrumentation 以替代系统的 Instrumentation，这样当系统通过 ActivityThread 调用 它的的成员变量 mInstrumentation 的 newActivity() 等方法的时候，实际是调用我们 VAInstrumentation 的 newActivity()。

实际上对于插件 Activity 启动，采用的是宿主 manifest 中占坑的方式来绕过系统校验，然后再加载真正的activity。

什么是占坑？就是构造一系列假的 Activity 替身，在 AndroidMainfest.xml 里面进行注册，以绕过检测，然后到了真正启动 Activity 的时候，再把它变回，去启动真正的目标 Activity。那么这一步是怎么做的呢？

我们可以打开核心库里面的 AndroidMainfest.xml 看看：

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<application>
    <!-- Stub Activities -->
    <activity android:name=".A$1" android:launchMode="standard"/>
    <activity android:name=".A$2" android:launchMode="standard"
        android:theme="@android:style/Theme.Translucent" />

    <!-- Stub Activities -->
    <activity android:name=".B$1" android:launchMode="singleTop"/>
    <activity android:name=".B$2" android:launchMode="singleTop"/>
    <activity android:name=".B$3" android:launchMode="singleTop"/>
    <activity android:name=".B$4" android:launchMode="singleTop"/>
    <activity android:name=".B$5" android:launchMode="singleTop"/>
    <activity android:name=".B$6" android:launchMode="singleTop"/>
    <activity android:name=".B$7" android:launchMode="singleTop"/>
    <activity android:name=".B$8" android:launchMode="singleTop"/>

    <!-- Stub Activities -->
    <activity android:name=".C$1" android:launchMode="singleTask"/>
    <activity android:name=".C$2" android:launchMode="singleTask"/>
    <activity android:name=".C$3" android:launchMode="singleTask"/>
    <activity android:name=".C$4" android:launchMode="singleTask"/>
    <activity android:name=".C$5" android:launchMode="singleTask"/>
    <activity android:name=".C$6" android:launchMode="singleTask"/>
    <activity android:name=".C$7" android:launchMode="singleTask"/>
    <activity android:name=".C$8" android:launchMode="singleTask"/>

    <!-- Stub Activities -->
    <activity android:name=".D$1" android:launchMode="singleInstance"/>
    <activity android:name=".D$2" android:launchMode="singleInstance"/>
    <activity android:name=".D$3" android:launchMode="singleInstance"/>
    <activity android:name=".D$4" android:launchMode="singleInstance"/>
    <activity android:name=".D$5" android:launchMode="singleInstance"/>
    <activity android:name=".D$6" android:launchMode="singleInstance"/>
    <activity android:name=".D$7" android:launchMode="singleInstance"/>
    <activity android:name=".D$8" android:launchMode="singleInstance"/>

</application>

可以发现，在清单里面注册了一堆假的 StubActivity。 ABCD分别对应不同的启动模式，那么，我们启动插件的 Activity 的时候，是如何把它改为清单里面已注册的这些假的 Activity 名呢？

在 VAInstrumentation 里面，重写了 startActivity 的必经之路，就是 execStartActivity() 方法：

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public ActivityResult execStartActivity(
            Context who, IBinder contextThread, IBinder token, Activity target,
            Intent intent, int requestCode, Bundle options) {
    
    // 这里面做了一系列操作，实际上就是查找插件里面第一个符合隐式条件的第一个ResolveInfo，并设置进intent
    mPluginManager.getComponentsHandler().transformIntentToExplicitAsNeeded(intent);
    // null component is an implicitly intent
    if (intent.getComponent() != null) {
        Log.i(TAG, String.format("execStartActivity[%s : %s]", intent.getComponent().getPackageName(),
                intent.getComponent().getClassName()));
        // ！！！ 重头戏在这里，用那些注册的假的StubActivity来替换真实的Activity，以绕过检测 ！！！
        this.mPluginManager.getComponentsHandler().markIntentIfNeeded(intent);
    }

    ActivityResult result = realExecStartActivity(who, contextThread, token, target,
                intent, requestCode, options);

    return result;

}

private ActivityResult realExecStartActivity(
        Context who, IBinder contextThread, IBinder token, Activity target,
        Intent intent, int requestCode, Bundle options) {
    ActivityResult result = null;
    try {
        Class[] parameterTypes = {Context.class, IBinder.class, IBinder.class, Activity.class, Intent.class,
        int.class, Bundle.class};
        result = (ActivityResult)ReflectUtil.invoke(Instrumentation.class, mBase,
                "execStartActivity", parameterTypes,
                who, contextThread, token, target, intent, requestCode, options);
    } catch (Exception e) {
        e.printStackTrace();
    }

    return result;
}

那么，是如何替换 StubActivity 的呢？ 跟进代码：

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public void markIntentIfNeeded(Intent intent) {
    if (intent.getComponent() == null) {
        return;
    }

    String targetPackageName = intent.getComponent().getPackageName();
    String targetClassName = intent.getComponent().getClassName();
    // 判断是否是启动插件的Activity
    if (!targetPackageName.equals(mContext.getPackageName()) && mPluginManager.getLoadedPlugin(targetPackageName) != null) {
        // 做标记
        intent.putExtra(Constants.KEY_IS_PLUGIN, true);
        // 保存真实的意图
        intent.putExtra(Constants.KEY_TARGET_PACKAGE, targetPackageName);
        intent.putExtra(Constants.KEY_TARGET_ACTIVITY, targetClassName);
        dispatchStubActivity(intent);
    }
}

/**
 * 真正的转换就在这里。根据启动模式，转换对应的 StubActivity
 */
private void dispatchStubActivity(Intent intent) {
    ComponentName component = intent.getComponent();
    String targetClassName = intent.getComponent().getClassName();
    LoadedPlugin loadedPlugin = mPluginManager.getLoadedPlugin(intent);
    ActivityInfo info = loadedPlugin.getActivityInfo(component);
    if (info == null) {
        throw new RuntimeException("can not find " + component);
    }
    int launchMode = info.launchMode;
    // 临时替换主题
    Resources.Theme themeObj = loadedPlugin.getResources().newTheme();
    themeObj.applyStyle(info.theme, true);
    
    // 实际上就是这一句，完成转换
    String stubActivity = mStubActivityInfo.getStubActivity(targetClassName, launchMode, themeObj);
    Log.i(TAG, String.format("dispatchStubActivity,[%s -> %s]", targetClassName, stubActivity));
    intent.setClassName(mContext, stubActivity);
}

继续跟进代码：

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class StubActivityInfo {
    public static final int MAX_COUNT_STANDARD = 1;
    public static final int MAX_COUNT_SINGLETOP = 8;
    public static final int MAX_COUNT_SINGLETASK = 8;
    public static final int MAX_COUNT_SINGLEINSTANCE = 8;

    public static final String corePackage = "com.didi.virtualapk.core";
    
    // 这个格式，就是那些假的Activity的名字
    public static final String STUB_ACTIVITY_STANDARD = "%s.A$%d";
    public static final String STUB_ACTIVITY_SINGLETOP = "%s.B$%d";
    public static final String STUB_ACTIVITY_SINGLETASK = "%s.C$%d";
    public static final String STUB_ACTIVITY_SINGLEINSTANCE = "%s.D$%d";

    public final int usedStandardStubActivity = 1;
    public int usedSingleTopStubActivity = 0;
    public int usedSingleTaskStubActivity = 0;
    public int usedSingleInstanceStubActivity = 0;

    private HashMap<String, String> mCachedStubActivity = new HashMap<>();
    
    /**
     * 在这里根据启动模式及主题构造 StubActivity 
     */
    public String getStubActivity(String className, int launchMode, Theme theme) {
        String stubActivity= mCachedStubActivity.get(className);
        if (stubActivity != null) {
            return stubActivity;
        }

        TypedArray array = theme.obtainStyledAttributes(new int[]{
                android.R.attr.windowIsTranslucent,
                android.R.attr.windowBackground
        });
        boolean windowIsTranslucent = array.getBoolean(0, false);
        array.recycle();
        if (Constants.DEBUG) {
            Log.d("StubActivityInfo", "getStubActivity, is transparent theme ? " + windowIsTranslucent);
        }
        stubActivity = String.format(STUB_ACTIVITY_STANDARD, corePackage, usedStandardStubActivity);
        switch (launchMode) {
            case ActivityInfo.LAUNCH_MULTIPLE: {
                stubActivity = String.format(STUB_ACTIVITY_STANDARD, corePackage, usedStandardStubActivity);
                if (windowIsTranslucent) {
                    stubActivity = String.format(STUB_ACTIVITY_STANDARD, corePackage, 2);
                }
                break;
            }
            case ActivityInfo.LAUNCH_SINGLE_TOP: {
                usedSingleTopStubActivity = usedSingleTopStubActivity % MAX_COUNT_SINGLETOP + 1;
                stubActivity = String.format(STUB_ACTIVITY_SINGLETOP, corePackage, usedSingleTopStubActivity);
                break;
            }
            case ActivityInfo.LAUNCH_SINGLE_TASK: {
                usedSingleTaskStubActivity = usedSingleTaskStubActivity % MAX_COUNT_SINGLETASK + 1;
                stubActivity = String.format(STUB_ACTIVITY_SINGLETASK, corePackage, usedSingleTaskStubActivity);
                break;
            }
            case ActivityInfo.LAUNCH_SINGLE_INSTANCE: {
                usedSingleInstanceStubActivity = usedSingleInstanceStubActivity % MAX_COUNT_SINGLEINSTANCE + 1;
                stubActivity = String.format(STUB_ACTIVITY_SINGLEINSTANCE, corePackage, usedSingleInstanceStubActivity);
                break;
            }

            default:break;
        }

        mCachedStubActivity.put(className, stubActivity);
        return stubActivity;
    }

}

到这一步，就基本清晰了。同样的，既然变为了 StubActivity，那么真正启动的时候还得变回来才行。来看一下重写后的 newActivity() 方法：

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@Override
public Activity newActivity(ClassLoader cl, String className, Intent intent) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
    try {
        cl.loadClass(className);
    } catch (ClassNotFoundException e) {
        // 根据 intent 类型，去获取相应的插件
        LoadedPlugin plugin = this.mPluginManager.getLoadedPlugin(intent);
        // 这里就是从Intent中取出我们刚才保存的真正的意图
        String targetClassName = PluginUtil.getTargetActivity(intent);

        Log.i(TAG, String.format("newActivity[%s : %s]", className, targetClassName));

        if (targetClassName != null) {
            // mBase 是未替换之前的 Instrumentation 对象，所以这个实际上是交给系统原先的 Instrumentation 对象去执行，所以这个模式其实也可以理解为与动态代理等同
            // plugin.getClassLoader() 是自己构造的一个 DexClassLoader，专门用于加载对应的apk里面的类
            Activity activity = mBase.newActivity(plugin.getClassLoader(), targetClassName, intent);
            activity.setIntent(intent);

            try {
                // for 4.1+
                ReflectUtil.setField(ContextThemeWrapper.class, activity, "mResources", plugin.getResources());
            } catch (Exception ignored) {
                // ignored.
            }

            return activity;
        }
    }

    return mBase.newActivity(cl, className, intent);
}

到这里，插件的 Activity 启动流程分析，就基本结束了。细节方面，没法一步到位，还需要大家边看源码边理解，这样才能看得更透彻。

Service 支持

对于 Service 的支持，采用动态代理AMS，拦截 Service 相关的请求，将其中转给Service Runtime去处理，Service Runtime会接管系统的所有操作。

对于我们动态代理AMS，在上一节 Activity支持 中已经介绍过了，那么，简单的来看一下 ActivityManagerProxy 是如何启动一个Service的。

在执行 startService 等方法的时候，AMS 代理对象会相应的来执行以下这些方法：

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private Object startService(Object proxy, Method method, Object[] args) throws Throwable {
    IApplicationThread appThread = (IApplicationThread) args[0];
    Intent target = (Intent) args[1];
    ResolveInfo resolveInfo = this.mPluginManager.resolveService(target, 0);
    if (null == resolveInfo || null == resolveInfo.serviceInfo) {
        // is host service
        return method.invoke(this.mActivityManager, args);
    }

    return startDelegateServiceForTarget(target, resolveInfo.serviceInfo, null, RemoteService.EXTRA_COMMAND_START_SERVICE);
}

private ComponentName startDelegateServiceForTarget(Intent target, ServiceInfo serviceInfo, Bundle extras, int command) {
    Intent wrapperIntent = wrapperTargetIntent(target, serviceInfo, extras, command);
    return mPluginManager.getHostContext().startService(wrapperIntent);
}

private Intent wrapperTargetIntent(Intent target, ServiceInfo serviceInfo, Bundle extras, int command) {
    // fill in service with ComponentName
    target.setComponent(new ComponentName(serviceInfo.packageName, serviceInfo.name));
    String pluginLocation = mPluginManager.getLoadedPlugin(target.getComponent()).getLocation();

    // 这里进行判断，看是交给 LocalService，还是 RemoteService 处理
    // LocalService 和 RemoteService 分别对应是否在新的进程中启动Activity
    boolean local = PluginUtil.isLocalService(serviceInfo);
    Class<? extends Service> delegate = local ? LocalService.class : RemoteService.class;
    Intent intent = new Intent();
    intent.setClass(mPluginManager.getHostContext(), delegate);
    intent.putExtra(RemoteService.EXTRA_TARGET, target);
    
    // 保存一下这个的Command,对应执行不同操作
    intent.putExtra(RemoteService.EXTRA_COMMAND, command);
    intent.putExtra(RemoteService.EXTRA_PLUGIN_LOCATION, pluginLocation);
    if (extras != null) {
        intent.putExtras(extras);
    }

    return intent;
}

实际上包括我们调用 stopService()，AMS 代理对象最后变换后的意图，同样也是上面代码的最后两个个方法 startDelegateServiceForTarget 和 wrapperTargetIntent()，只不过 command 不一样。

所以本质上 AMS 作为代理，不管你执行启动或者关闭插件里面的 Service，他都是调用 LocalService 或者 RemoteService 的 startService 方法，在 LocalService 或者 RemoteService 的 onStartCommand() 下，根据 command 进行相应的操作。那么我们来看一下 LocalService 的 onStartCommand() 方法：

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@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    if (null == intent || !intent.hasExtra(EXTRA_TARGET) || !intent.hasExtra(EXTRA_COMMAND)) {
        return START_STICKY;
    }

    Intent target = intent.getParcelableExtra(EXTRA_TARGET);
    int command = intent.getIntExtra(EXTRA_COMMAND, 0);
    if (null == target || command <= 0) {
        return START_STICKY;
    }

    ComponentName component = target.getComponent();
    LoadedPlugin plugin = mPluginManager.getLoadedPlugin(component);

    switch (command) {
        case EXTRA_COMMAND_START_SERVICE: {
            ActivityThread mainThread = (ActivityThread)ReflectUtil.getActivityThread(getBaseContext());
            IApplicationThread appThread = mainThread.getApplicationThread();
            Service service;

            if (this.mPluginManager.getComponentsHandler().isServiceAvailable(component)) {
                service = this.mPluginManager.getComponentsHandler().getService(component);
            } else {
                try {
                    service = (Service) plugin.getClassLoader().loadClass(component.getClassName()).newInstance();

                    Application app = plugin.getApplication();
                    IBinder token = appThread.asBinder();
                    Method attach = service.getClass().getMethod("attach", Context.class, ActivityThread.class, String.class, IBinder.class, Application.class, Object.class);
                    IActivityManager am = mPluginManager.getActivityManager();

                    attach.invoke(service, plugin.getPluginContext(), mainThread, component.getClassName(), token, app, am);
                    service.onCreate();
                    this.mPluginManager.getComponentsHandler().rememberService(component, service);
                } catch (Throwable t) {
                    return START_STICKY;
                }
            }

            service.onStartCommand(target, 0, this.mPluginManager.getComponentsHandler().getServiceCounter(service).getAndIncrement());
            break;
        }
        case EXTRA_COMMAND_BIND_SERVICE: {
            ActivityThread mainThread = (ActivityThread)ReflectUtil.getActivityThread(getBaseContext());
            IApplicationThread appThread = mainThread.getApplicationThread();
            Service service = null;

            if (this.mPluginManager.getComponentsHandler().isServiceAvailable(component)) {
                service = this.mPluginManager.getComponentsHandler().getService(component);
            } else {
                try {
                    service = (Service) plugin.getClassLoader().loadClass(component.getClassName()).newInstance();

                    Application app = plugin.getApplication();
                    IBinder token = appThread.asBinder();
                    Method attach = service.getClass().getMethod("attach", Context.class, ActivityThread.class, String.class, IBinder.class, Application.class, Object.class);
                    IActivityManager am = mPluginManager.getActivityManager();

                    attach.invoke(service, plugin.getPluginContext(), mainThread, component.getClassName(), token, app, am);
                    service.onCreate();
                    this.mPluginManager.getComponentsHandler().rememberService(component, service);
                } catch (Throwable t) {
                    t.printStackTrace();
                }
            }
            try {
                IBinder binder = service.onBind(target);
                IBinder serviceConnection = PluginUtil.getBinder(intent.getExtras(), "sc");
                IServiceConnection iServiceConnection = IServiceConnection.Stub.asInterface(serviceConnection);
                iServiceConnection.connected(component, binder);
            } catch (Exception e) {
                e.printStackTrace();
            }
            break;
        }
        case EXTRA_COMMAND_STOP_SERVICE: {
            Service service = this.mPluginManager.getComponentsHandler().forgetService(component);
            if (null != service) {
                try {
                    service.onDestroy();
                } catch (Exception e) {
                    Log.e(TAG, "Unable to stop service " + service + ": " + e.toString());
                }
            } else {
                Log.i(TAG, component + " not found");
            }
            break;
        }
        case EXTRA_COMMAND_UNBIND_SERVICE: {
            Service service = this.mPluginManager.getComponentsHandler().forgetService(component);
            if (null != service) {
                try {
                    service.onUnbind(target);
                    service.onDestroy();
                } catch (Exception e) {
                    Log.e(TAG, "Unable to unbind service " + service + ": " + e.toString());
                }
            } else {
                Log.i(TAG, component + " not found");
            }
            break;
        }
    }

    return START_STICKY;
}

很显然，在这里面才对应去控制了插件Service的生命周期。具体代码就留给大家分析吧~~

ContentProvider 支持

动态代理 IContentProvider，拦截provider相关的请求，将其中转给Provider Runtime去处理，Provider Runtime会接管系统的所有操作。

我们来看一下 com.didi.virtualapk.internal.PluginContentResolver 这个类：

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public class PluginContentResolver extends ContentResolver {
    private ContentResolver mBase;
    private PluginManager mPluginManager;
    private static Method sAcquireProvider;
    private static Method sAcquireExistingProvider;
    private static Method sAcquireUnstableProvider;

    static {
        try {
            sAcquireProvider = ContentResolver.class.getDeclaredMethod("acquireProvider",
                    new Class[]{Context.class, String.class});
            sAcquireProvider.setAccessible(true);
            sAcquireExistingProvider = ContentResolver.class.getDeclaredMethod("acquireExistingProvider",
                    new Class[]{Context.class, String.class});
            sAcquireExistingProvider.setAccessible(true);
            sAcquireUnstableProvider = ContentResolver.class.getDeclaredMethod("acquireUnstableProvider",
                    new Class[]{Context.class, String.class});
            sAcquireUnstableProvider.setAccessible(true);
        } catch (Exception e) {
            //ignored
        }
    }

    public PluginContentResolver(Context context) {
        super(context);
        mBase = context.getContentResolver();
        mPluginManager = PluginManager.getInstance(context);
    }

    protected IContentProvider acquireProvider(Context context, String auth) {
        try {
            if (mPluginManager.resolveContentProvider(auth, 0) != null) {
                // 在这里，去 hook 一个 IContentProvider 代理对象
                return mPluginManager.getIContentProvider();
            }

            return (IContentProvider) sAcquireProvider.invoke(mBase, context, auth);
        } catch (Exception e) {
            e.printStackTrace();
        }

        return null;
    }
    
    // ...
}

这个类是在构造 LoadedPlugin 的时候创建的 PluginContext 对象里面的 getContentResolver() 里面创建的。

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class PluginContext extends ContextWrapper {

    private final LoadedPlugin mPlugin;

    public PluginContext(LoadedPlugin plugin) {
        super(plugin.getPluginManager().getHostContext());
        this.mPlugin = plugin;
    }

    @Override
    public ContentResolver getContentResolver() {
        // 创建代理支持
        return new PluginContentResolver(getHostContext());
    }
}

那么，上面Hook 的 IContentProvider 代理对象，实际上是在 PluginManager 做的。

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private void hookIContentProviderAsNeeded() {
    Uri uri = Uri.parse(PluginContentResolver.getUri(mContext));
    mContext.getContentResolver().call(uri, "wakeup", null, null);
    try {
        Field authority = null;
        Field mProvider = null;
        ActivityThread activityThread = (ActivityThread) ReflectUtil.getActivityThread(mContext);
        Map mProviderMap = (Map) ReflectUtil.getField(activityThread.getClass(), activityThread, "mProviderMap");
        Iterator iter = mProviderMap.entrySet().iterator();
        while (iter.hasNext()) {
            Map.Entry entry = (Map.Entry) iter.next();
            Object key = entry.getKey();
            Object val = entry.getValue();
            String auth;
            if (key instanceof String) {
                auth = (String) key;
            } else {
                if (authority == null) {
                    authority = key.getClass().getDeclaredField("authority");
                    authority.setAccessible(true);
                }
                auth = (String) authority.get(key);
            }
            if (auth.equals(PluginContentResolver.getAuthority(mContext))) {
                if (mProvider == null) {
                    mProvider = val.getClass().getDeclaredField("mProvider");
                    mProvider.setAccessible(true);
                }
                IContentProvider rawProvider = (IContentProvider) mProvider.get(val);
                IContentProvider proxy = IContentProviderProxy.newInstance(mContext, rawProvider);
                mIContentProvider = proxy;
                Log.d(TAG, "hookIContentProvider succeed : " + mIContentProvider);
                break;
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

这一块的内容，最好根据滴滴提供的Demo，再来看，比较容易理解。

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Uri bookUri = Uri.parse("content://com.ryg.chapter_2.book.provider/book");
ContentValues values = new ContentValues();
values.put("_id", 6);
values.put("name", "程序设计的艺术");

Receiver 支持

官方解释是将插件中静态注册的receiver重新注册一遍。在代码里貌似没找到相应的支持，Demo 里也没有，或许这部分还没完成吧？？

小结

本文重点在于分析插件的 Activity 启动流程，其他包括主题、资源，并没有详细分析，因为说细了内容还是有点多了，主要是让大伙儿在阅读代码时，有个大致的方向。有疑问欢迎一起探讨哟~~

感谢阅读！

所长Android Development Engineer