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;
    }