在windowphone，ios和android中到目前为止，还是android的市场份额最大。个人认为除了google开源外，广大开发者早就了android的霸主地位。各位兄弟姐妹开发出各种各样的apk，才组成android的广阔天下。本篇主要分析一下android系统是针对处理这些apk的，主要涉及到pm这块的代码。分析这种底层服务，最好从android的开启启动流程中开始分析。因为这样才能更清楚的了解服务的启动流程。

1.在SystemServer.java 中启动PM

  android 开机启动后加载的第一个java的程序就是SystemServer,在包含android系统的最主要的一些底层服务。在4.4kk之前都是建一个Thread线程来启动。4.4KK的启动机制就变了，具体后续的文章会讲解。

Installer installer = null;   
Slog.i(TAG, "Waiting for installd to be ready.");
            installer = new Installer();
            installer.ping();

 pm = PackageManagerService.main(context, installer,
                    factoryTest != SystemServer.FACTORY_TEST_OFF,
                    onlyCore);
            boolean firstBoot = false;
            try {
                firstBoot = pm.isFirstBoot();
            } catch (RemoteException e) {
            }

 public static final IPackageManager main(Context context, Installer installer,
            boolean factoryTest, boolean onlyCore) {
        PackageManagerService m = new PackageManagerService(context, installer,
                factoryTest, onlyCore);
        ServiceManager.addService("package", m);
        return m;
    }

2.PackageManagerService启动安装分析

启动PackageManagerService后，主要完成以下几个步骤

2.1.初始化PackageSetting，设置sharedUserID

mSettings = new Settings(context);
        mSettings.addSharedUserLPw("android.uid.system",
                Process.SYSTEM_UID, ApplicationInfo.FLAG_SYSTEM);
        mSettings.addSharedUserLPw("android.uid.phone", RADIO_UID, ApplicationInfo.FLAG_SYSTEM);

 WindowManager wm = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);
        Display d = wm.getDefaultDisplay();
        d.getMetrics(mMetrics);

mHandlerThread.start();
            mHandler = new PackageHandler(mHandlerThread.getLooper());

            File dataDir = Environment.getDataDirectory();
            mAppDataDir = new File(dataDir, "data");
            mAppInstallDir = new File(dataDir, "app");
            mAppLibInstallDir = new File(dataDir, "app-lib");
            mAsecInternalPath = new File(dataDir, "app-asec").getPath();
            mUserAppDataDir = new File(dataDir, "user");
            mDrmAppPrivateInstallDir = new File(dataDir, "app-private");

 mFrameworkDir = new File(Environment.getRootDirectory(), "framework");
            mDalvikCacheDir = new File(dataDir, "dalvik-cache");

            boolean didDexOpt = false;

            /**
             * Out of paranoia, ensure that everything in the boot class
             * path has been dexed.
             */
            String bootClassPath = System.getProperty("java.boot.class.path");

// Collect all system packages.
            mSystemAppDir = new File(Environment.getRootDirectory(), "app");
            mSystemInstallObserver = new AppDirObserver(
                mSystemAppDir.getPath(), OBSERVER_EVENTS, true);
            mSystemInstallObserver.startWatching();
            scanDirLI(mSystemAppDir, PackageParser.PARSE_IS_SYSTEM
                    | PackageParser.PARSE_IS_SYSTEM_DIR, scanMode, 0);

            // Collect all vendor packages.
            mVendorAppDir = new File("/vendor/app");
            mVendorInstallObserver = new AppDirObserver(
                mVendorAppDir.getPath(), OBSERVER_EVENTS, true);
            mVendorInstallObserver.startWatching();
            scanDirLI(mVendorAppDir, PackageParser.PARSE_IS_SYSTEM
                    | PackageParser.PARSE_IS_SYSTEM_DIR, scanMode, 0);

......
 mAppInstallObserver = new AppDirObserver(
                    mAppInstallDir.getPath(), OBSERVER_EVENTS, false);
                mAppInstallObserver.startWatching();
                scanDirLI(mAppInstallDir, 0, scanMode, 0);
    

其中具体如果安装代码在scanDirLI（）函数，最终调用scanPackageLI（）进行安装。在安装过程中会搜集ApplicationInfo和ActivityInfo信息，比较签名，匹配本地so的目录。

具体细节参看PackageManagerService.java 中的

函数。

3.在Activity使用PackageManger的分析

   我们在应用经常通过

   PackageManager pm = this.getPackageManager() 来获取pm。这部分主要从它的来源来深入分析。

  由于我们在Activity中使用this来获取pm，很容易想到到context类里去寻找实现。

 /** Return PackageManager instance to find global package information. */
    public abstract PackageManager getPackageManager();

果然找到。

   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;
    }

那我们就看看他是怎么实现的

 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;
    }

通过asInterface（）函数，通过binder对象获取接口类IPackageManager的实例。并返回回去。

if (pm != null) {
            // Doesn‘t matter if we make more than one instance.
            return (mPackageManager = new ApplicationPackageManager(this, pm));
        }

在接着同ApplicationPackageManager 创建PackageManager 对象。到此我们在Activity中就可以使用pm这个对象操作系统中的各种包。

4.Android 系统中PackageManager的关键类和UML的类图。

 在pm中主要涉及的类和路径如下：

 frameworks\base\services\java\com\android\server\pm\PackageManagerService.java 和 其他文件

frameworks\base\core\java\android\content\pm\IPackageManager.aidl

frameworks\base\core\java\android\app\ActivityThread.java ,context.java ,contextimpl.java

frameworks\base\core\java\android\content\pm\PackageManager.java

Android Framework 分析---PackageManager 分析,布布扣,bubuko.com

Android Framework 分析---PackageManager 分析