Android FrameWork——PackageManager框架

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