1.接着前面讲的ActivityManager框架，继续说一下系统另一个重要的框架，PackagerManager

同样先看一下静态类结构图：

大 部分情况我们是在Activity中使用getPackageManager方法获取一个ApplicationPackageManager的对 象，ApplicationPackageManager实际上是包装了一个IPackageManager.Stub.Proxy的对象

由IPackageManager.Stub.Proxy代理执行PackageManager相关操作，IPackageManager.Stub.Proxy实际代理的是PackageManagerService,

2.看了前面说的，可能你有点晕，我们再来重新理一下：

        首先是IPackageManager是通过IPackageManager.aidl文件生成，同时生成了存根类IPackageManager.Stub，代理类：IPackageManager.Stub.Proxy

这个是packageManager进程通信的基本框架，我前面blog有说，不多加说明了

        然后PackageManagerService，它继承了IPackageManager.Stub,它作为PackageManager动作的实际执行者，在system_process中存在

        再是我们用户应用程序中的ApplicationPackageManager,先看它如何被获取的：

ContextImpl.java中有一个方法：

    public PackageManager getPackageManager() {

        if (mPackageManager != null) {

            return mPackageManager;

        }

        IPackageManager pm = ActivityThread.getPackageManager();

        if (pm != null) {

            // Doesn't matter if we make more than one instance.

            return (mPackageManager = new ApplicationPackageManager(this, pm));

        }

        return null;

    }

ApplicationPackageManager实际上是包装了一个IPackageManager对象(IPackageManager.Stub.Proxy),当我们调用queryIntentActivities时，实际通过代理对象去执行：

    public List<ResolveInfo> queryIntentActivities(Intent intent,

                int flags) {

            try {

                return mPM.queryIntentActivities(//mPM是IPackageManager.Stub.Proxy对象

                    intent,

                    intent.resolveTypeIfNeeded(mContext.getContentResolver()),

                    flags);

            } catch (RemoteException e) {

                throw new RuntimeException("Package manager has died", e);

            }

        }

进过进程通信，在PackageManagerService执行对应操作：

3.PackageManagerService的构建与获取

--PackageManagerService 的构建：在system_process进程加载时，PackageManagerService被构建，在 SystemServer.ServerThread.run中有如下一段代码，它就是加载  PackageManagerService的：

            Slog.i(TAG, "Package Manager");

            pm = PackageManagerService.main(context,

                    factoryTest != SystemServer.FACTORY_TEST_OFF);//启动PackageManagerService

///PackageManagerService///

    public static final IPackageManager main(Context context, boolean factoryTest) {

        PackageManagerService m = new PackageManagerService(context, factoryTest);

        ServiceManager.addService("package", m);

        return m;

    }

    --PackageManagerService获取:      

    先看前面在ContextImpl.java->getPackagerManager中：   

       IPackageManager pm = ActivityThread.getPackageManager();

/ActivityThread

        public static IPackageManager getPackageManager() {

        if (sPackageManager != null) {

            //Slog.v("PackageManager", "returning cur default = " + sPackageManager);

            return sPackageManager;

        }

        IBinder b = ServiceManager.getService("package");

        //Slog.v("PackageManager", "default service binder = " + b);

        sPackageManager = IPackageManager.Stub.asInterface(b);

        //Slog.v("PackageManager", "default service = " + sPackageManager);

        return sPackageManager;

    }

     从ServiceManager中获取的服务pakager,该服务在.PackageManagerService的构建时被注册到 ServiceManager中的，ServiceManager机制暂时没有深入了解，后面再发blog专门说一下ServiceManager

 原文：http://blog.csdn.net/stonecao/article/details/6591454