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：
package_manager_gv
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;
}
