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

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;
}