Android应用生死轮回的那些事儿(2) - PackageManager

PMS对外的接口

如我们上节所讲，在Android中，为应用包的安装，删除各种操作服务的，是PackageManagerSerivce，简称PMS.

如果想要调用PMS的服务，则可以通过Context去调用getPackageManager方法。

这个定义于Context.java中：

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

我们先来看一张图，了解PackageManager与PMS的关系：

PackageManager中定义的方法的前因后果

我们下面先以PackageManager中所提供的getApplicationInfo方法为例，看看它是如何被实现的。

PackageManager中的定义

ApplicationInfo getApplicationInfo (String packageName,int flags)

• packageName:包名
• flags:支持下面的标志：

支持的标志如下：

• GET_SHARED_LIBRARY_FILES：获取so库的安装路径，然后可以通过ApplicationInfo的sharedLibraryFiles属性来读取相关信息。
• MATCH_SYSTEM_ONLY:只包括带有系统属性的
• MATCH_UNINSTALLED_PACKAGES：即使是应用被uninstall了，但只要保留了数据，也可以被搜出来。

public abstract PackageInfo getPackageInfo(String packageName, int flags)throws NameNotFoundException;

PackageManager的实现 - ApplicationPackageManager

ApplicationPackageManager继承了抽象类PackageManager.

final class ApplicationPackageManager extends PackageManager

ApplicationPackageManager是在ContextImpl中被new出来的：

@Override    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中的第二个参数pm是沟通PMS的桥梁。

我们来看ActivityThread中getPackageManager的实现：

public static IPackageManager getPackageManager() {        if (sPackageManager != null) {            return sPackageManager;        }        IBinder b = ServiceManager.getService("package");        sPackageManager = IPackageManager.Stub.asInterface(b);        return sPackageManager;    }

ApplicationPackageManager中的实现

在ApplicationPackageManager类中，其实还是对PMS的对应功能的封装。

public ApplicationInfo getApplicationInfo(String packageName, int flags)            throws NameNotFoundException {        try {            ApplicationInfo ai = mPM.getApplicationInfo(packageName, flags, mContext.getUserId());...        } catch (RemoteException e) {            throw new RuntimeException("Package manager has died", e);        }        throw new NameNotFoundException(packageName);    }

PackageManagerService中真正落地

真正的实现还是要看PMS:

@Override    public ApplicationInfo getApplicationInfo(String packageName, int flags, int userId) {        if (!sUserManager.exists(userId)) return null;        enforceCrossUserPermission(Binder.getCallingUid(), userId, false, false, "get application info");        // writer        synchronized (mPackages) {            PackageParser.Package p = mPackages.get(packageName);            if (DEBUG_PACKAGE_INFO) Log.v(                    TAG, "getApplicationInfo " + packageName                    + ": " + p);            if (p != null) {                PackageSetting ps = mSettings.mPackages.get(packageName);                if (ps == null) return null;                // Note: isEnabledLP() does not apply here - always return info                return PackageParser.generateApplicationInfo(                        p, flags, ps.readUserState(userId), userId);            }            if ("android".equals(packageName)||"system".equals(packageName)) {                return mAndroidApplication;            }            if ((flags & PackageManager.GET_UNINSTALLED_PACKAGES) != 0) {                return generateApplicationInfoFromSettingsLPw(packageName, flags, userId);            }        }        return null;    }